The Project Gutenberg eBook of A handbook of systematic botany, by Johannes Eugenius Warming

Title: A handbook of systematic botany

Author: Johannes Eugenius Warming

Translator: Michael Cresse Potter

Contributor: Emil Friedrich Knoblauch

Release Date: July 21, 2022 [eBook #68580]

Language: English

Produced by: Peter Becker, Karin Spence and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive)

A HANDBOOK
OF
SYSTEMATIC BOTANY

BY

DR. E. WARMING

Professor of Botany in the University of Copenhagen

With a Revision of the Fungi by
DR. E. KNOBLAUCH,
Karlsruhe

Translated and Edited by
M. C. POTTER, M.A. F.L.S.

Professor of Botany in the University of Durham
College of Science, Newcastle-upon-Tyne
Author of “An Elementary Text-book of Agricultural Botany”

WITH 610 ILLUSTRATIONS

London

SWAN SONNENSCHEIN & CO

NEW YORK: MACMILLAN & CO

1895

Butler & Tanner,
The Selwood Printing Works,
Frome, and London.

The present translation of Dr. E. Warming’s Haandbog i den Systematiske Botanik is taken from the text of the 3rd Danish Edition (1892), and from Dr. Knoblauch’s German Edition (1890), and the book has been further enriched by numerous additional notes which have been kindly sent to me by the author. Dr. Warming’s work has long been recognised as an original and important contribution to Systematic Botanical Literature, and I have only to regret that the pressure of other scientific duties has delayed its presentation to English readers. Dr. Warming desires me to record his high appreciation of the careful translation of Dr. Knoblauch, and his obligation to him for a number of corrections and improvements of which he has made use in the 3rd Danish Edition. In a few instances I have made slight additions to the text; these, however, appear as footnotes, or are enclosed in square brackets.

In the present Edition the Thallophytes have been revised and rearranged from notes supplied to me by Dr. Knoblauch, to whom I am indebted for the Classification of the Fungi, according to the more recent investigations of Brefeld. The Bacteria have been revised by Dr. Migula, the Florideæ rearranged after Schmitz, and the Taphrinaceæ after Sadebeck. The main body of the text of the Algæ and Fungi remains as it was originally written by Dr. Wille and Dr. Rostrup in the Danish Edition, though in many places considerable alterations and additions have been made. For the sake of comparison a tabular key to the Classification adopted in the Danish Edition is given in the Appendix.

In the Angiosperms I have retained the sequence of orders in the Danish original, and have not rearranged them according to[vi] the systems more familiar to English students. In any rearrangement much of the significance of Dr. Warming’s valuable and original observations would have been lost, and also from a teacher’s point of view I have found this system of great value. Although at present it may not be completely satisfactory, yet as an attempt to explain the mutual relationships, development and retrogression of many of the orders, it may be considered to have a distinct advantage over the more artificial systems founded upon Jussieu’s Divisions of Polypetalæ, Gamopetalæ, and Apetalæ.

With reference to the principles of the systematic arrangement adopted, I may here insert the following brief communication from the author (dated March, 1890), which he has requested me to quote from the preface of Dr. Knoblauch’s edition:—“Each form which, on comparative morphological considerations, is clearly less simple, or can be shown to have arisen by reduction or through abortion of another type having the same fundamental structure, or in which a further differentiation and division of labour is found, will be regarded as younger, and as far as possible, and so far as other considerations will admit, will be reviewed later than the ‘simpler,’ more complete, or richer forms. For instance, to serve as an illustration: Epigyny and Perigyny are less simple than Hypogny; the Epigynous Sympetalæ, Choripetalæ, Monocotyledones are, therefore, treated last, the Hydrocharitaceæ are considered last under the Helobieæ, etc. Zygomorphy is younger than Actinomorphy; the Scitamineæ and Gynandræ therefore follow after the Liliifloræ, the Scrophulariaceæ after the Solanaceæ, Linaria after Verbascum, etc. Forms with united leaves indicate younger types than those with free leaves; hence the Sympetalæ come after the Choripetalæ, the Sileneæ after the Alsineæ, the Malcaceæ after the Sterculiaceæ and Tiliaceæ, etc.

“Acyclic (spiral-leaved) flowers are older than cyclic (verticillate-leaved) with a definite number, comparing, of course, only those with the same fundamental structure. The Veronica-type must be considered as younger, for example, than Digitalis and Antirrhinum,[vii] these again as younger than Scrophularia; Verbascum, on the contrary, is the least reduced, and therefore considered as the oldest form. Similarly the one-seeded, nut-fruited Ranunculaceæ are considered as a later type (with evident abortion) than the many-seeded, folicular forms of the Order; the Paronychieæ and Chenopodiaceæ as reduced forms of the Alsineæ type; and the occurrence of few seeds in an ovary as generally arising through reduction of the many-seeded forms. The Cyperaceæ are regarded as a form derived from the Juncaceæ through reduction, and associated with this, as is so often the case, there is a complication of the inflorescence; the Dipsacaceæ are again regarded as a form proceeding from the Valerianaceæ by a similar reduction, and these in their turn as an offshoot from the Caprifoliaceæ, etc. Of course these principles of systematic arrangement could only be applied very generally; for teaching purposes they have often required modification.”

In preparing the translation considerable difficulty has been experienced in finding a satisfactory rendering of several terms which have no exact equivalent in English. I may here especially mention the term Vorblatt (Forblad) which I have translated by the term bracteole, when it clearly applied to the first leaf (or leaves) on a pedicel; but in discussing questions of general morphology a term was much needed to include both vegetative and floral shoots, and for this I have employed the term “Fore-leaf.” Also, the term “Floral-leaf” has been adopted as an equivalent of “Hochblatt,” and the term “bract” has been limited to a leaf subtending a flower. I have followed Dr. E. L. Mark in translating the word “Anlage” by “Fundament.”

At the end of the book will be found a short appendix giving an outline of some of the earlier systems of Classification, with a more complete account of that of Hooker and Bentham.

In a book of this character it is almost impossible to avoid some errors, but it is hoped that these will be comparatively few. In correcting the proof-sheets I have received invaluable assistance from Dr. Warming and Dr. Knoblauch, who have kindly[viii] read through every sheet, and to whom I am greatly indebted for many criticisms and suggestions. I have also to thank Mr. I. H. Burkill for his kind assistance in looking over the proofs of the Monocotyledons and Dicotyledons, and Mr. Harold Wager for kindly reading through the proofs of the Algæ and Fungi. My thanks are also especially due to Mr. E. L. Danielsen, and I wish to take this opportunity of acknowledging the very considerable help which I have received from him in translating from the Original Danish.

M. C. POTTER.

January, 1895.

BEING THE SYSTEM OF CLASSIFICATION ADOPTED IN THE PRESENT VOLUME.

(The Algæ and Fungi rearranged in co-operation with Dr. E. Knoblauch, the other Divisions as in the 3rd Danish Edition.)

• Page 9, line 12 from top, for Hydrodicton read Hydrodictyon.
•  „  14, lines 1 and 2 from top, for as in the preceding case read in this case.
•  „  14, „  2 and 15 from top, for zygote read oospore.
•  „  88, line 15 from bottom, for Periphyses read periphyses.
•  „  124, „  7 „   „  for Chæromyces read Choiromyces.
•  „  142, „  2 „   „  and in Fig. 137, for Bœomyces read Bæomyces.
•  „  152, „  2 „  top, for Pirus read Pyrus.
•  „  152, „  5 „   „  for Crategus read Cratægus.
•  „  216, Fig. 215, for Salvina read Salvinia.
•  „  306, line 6 from top, for Pista read Pistia.
•  „  316, „  26 „   „  after Dracæna insert a comma.
•  „  337, „  13 „   „  for end read beginning.
•  „  483, „  11 „  bottom, for Lagerstrœmia read Lagerstrœmeria.

For ä, ö and ü read æ, œ and ue throughout.

The following are not officinal in the British Pharmacopœia:—page 316, Dracæna (Dragon’s-blood), Smilax glabra; p. 321, “Orris-root”; p. 326, species of Curcuma, Alpinia officinarum; p. 333, Orchis-species (“Salep”). On page 296, par. 4, only Pearl Barley is offic. in the Brit. Phar.

The Vegetable Kingdom is arranged in 5 Divisions.

Division I.—Thallophyta, Stemless Plants, or those which are composed of a “thallus,” i.e. organs of nourishment which are not differentiated into root (in the sense in which this term is used among the higher plants), stem, or leaf. Vascular bundles are wanting. Conjugation and fertilisation in various ways; among most of the Fungi only vegetative multiplication.

The Thallophytes are again separated into 3 sub-divisions, namely:

• Sub-Division A.—Myxomycetes, Slime-Fungi, with only 1 class.
• Sub-Division B.—Algæ, with 10 classes:
• Class 1. Syngeneticæ.
•  „ 2. Dinoflagellata, Peridinea.
•  „ 3. Diatomeæ, Diatoms.
•  „ 4. Schizophyta, Fission Algæ.
•  „ 5. Conjugatæ.
•  „ 6. Chlorophyceæ, Green Algæ.
•  „ 7. Characeæ, Stone-worts.
•  „ 8. Phæophyceæ, Brown Algæ.
•  „ 9. Dictyotales.
•  „ 10. Rhodophyceæ, Red Algæ.
• Sub-Division C.—Fungi, with 3 classes:
• Class 1. Phycomycetes.
•  „ 2. Mesomycetes.
•  „ 3. Mycomycetes, Higher Fungi.

Division II.—Bryophyta or Muscineæ, Mosses. These have leaf-bearing shoots, but neither true roots nor vascular[2] bundles. The lowest Mosses have, however, a thallus. Fertilisation is accomplished by means of self-motile, spirally coiled spermatozoids, through the agency of water. From the fertilised oosphere a “fruit-body” (capsule) with unicellular organs of reproduction (spores) is produced. The spore on germination gives rise to the vegetative system, which bears the organs of sexual reproduction; and this system is divided into two stages—the protonema, and the leaf-bearing plant produced on it.

Alternation of generations:

•  I. The protonema and the entire nutritive system which bears the organs of sexual reproduction.
• II. The capsule-like sporangium, with spores.
•  2 Classes: 1. Hepaticæ, Liverworts.
• 2. Musci, Leafy Mosses.

Division III.—Pteridophyta or Vascular Cryptogams, Fern-like Plants having leaf-bearing shoots, true roots, and vascular bundles with tracheides and sieve-tubes. Fertilisation as in the Mosses. From the fertilised oosphere the leaf-bearing shoot arises, which bears on its leaves the reproductive organs, the spores, in capsule-like sporangia. From the germination of the spore a small prothallium is formed, which bears the sexual reproductive organs.

Alternation of generations:

•  I. Prothallium with organs of sexual reproduction.
• II. Leaf-bearing shoot with capsule-like sporangia.
•  3 Classes: 1. Filicinæ, True Ferns.
• 2. Equisetinæ, Horsetails.
• 3. Lycopodinæ, Club-mosses.

Division IV.—Gymnospermæ. The vegetative organs are in the main similar to those in the 3rd Division; special shoots are modified into flowers for the service of reproduction. From the oosphere, which is fertilised by means of the pollen-tube, the leaf-bearing plant is derived; this passes the first period of its life as an embryo in the seed, and continues its development when the germination of the seed takes place. The organs corresponding to the spores of the two preceding Divisions, are called respectively the pollen-grain and embryo-sac. The pollen-grains are multicellular; i.e. they contain an indistinct prothallium. In the embryo-sac a prothallium, rich in reserve material (endosperm),[3] with female organs of reproduction, is developed BEFORE FERTILISATION. The pollen-grains are carried by means of the wind to the ovules; these enclose the embryo-sac, and are situated on the open fruit-leaf (carpel), which has no stigma.

Alternation of generations:

•  I. Prothallium = Endosperm in ovule.
• II. Leaf-bearing plant, with flowers which produce the pollen-sac and ovule.
•  3 Classes: 1. Cycadeæ.
• 2. Coniferæ.
• 3. Gnetaceæ.

Division V.—Angiospermæ. The members of this group are very similar to those of Division IV. The ovules are, however, encased in closed fruit-leaves (ovary), which have a special portion (stigma) adapted for the reception and germination of the pollen-grains. The pollen-grains are bicellular, but with only a membrane separating the two nuclei; they are carried to the stigma by animals (chiefly insects), by the wind, or by some other means. Endosperm is not formed till AFTER FERTILISATION. Alternation of generations in the main as in the Gymnosperms, but less distinct; while the sexual generation, the prothallium, with the organs of fertilisation, is also strongly reduced.

• 2 Classes:[1] 1. Monocotyledones. Embryo with one seed-leaf.
• 2. Dicotyledones. Embryo with two seed-leaves.

The thallus in the simplest forms is unicellular; in the majority, however, it is built up of many cells, which in a few instances are exactly similar; but generally there is a division of labour, so that certain cells undertake certain functions and are constructed accordingly, while others have different work and corresponding structure. Vessels or similar high anatomical structures are seldom formed, and the markings on the cell-wall are with few exceptions very simple. The Myxomycetes occupy quite an isolated position; their organs of nourishment are naked masses of protoplasm (plasmodia).

As regards the external form, the thallus may be entirely without special prominences (such as branches, members), but when such are present they are all essentially alike in their origin and growth, that is, disregarding the hair-structures which may be developed. A shoot of a Seaweed or of a Lichen, etc., is essentially the same as any other part of the plant; only among the highest Algæ (Characeæ, certain Siphoneæ, Sargassum, and certain Red Seaweeds) do we find the same differences between the various external organs of the plant body as between stem and leaf, so that they must be distinguished by these names.

Roots of the same structure and development as in the Seed-plants are not found, but organs of attachment (rhizoids and haptera) serve partly the biological functions of the root.

Systematic division of the Thallophytes. To the Thallophytes belong three sub-divisions—Slime-Fungi, Algæ, and Fungi. Formerly the Thallophytes were divided into Algæ, Fungi, and Lichens. But this last group must be placed among the Fungi, since they are really Fungi, which live symbiotically with Algæ. The Slime-Fungi must be separated from the true Fungi as a distinct subdivision. The Algæ possess a colouring substance, which is generally green, brown, or red, and by means of which they are able to build up organic compounds from carbonic acid and water. The Bacteria, especially, form an exception to the Algæ in this respect; like the Fungi and Slime-Fungi they have as a rule no such colouring material, but must have organic carbonaceous food; these plants form no starch, and need no light[5] for their vegetation (most Fungi require light for fructification). The Myxomycetes, Bacteria, and Fungi derive their nourishment either as saprophytes from dead animal or vegetable matter, or as parasites from living animals or plants (hosts), in which they very often cause disease.

Sub-Division I.—MYXOMYCETES, SLIME-FUNGI.

The Slime-Fungi occupy quite an isolated position in the Vegetable Kingdom, and are perhaps the most nearly related to the group of Rhizopods in the Animal Kingdom. They live in and on organic remains, especially rotten wood or leaves, etc., on the surface of which their sporangia may be found.

They are organisms without chlorophyll, and in their vegetative condition are masses of protoplasm without cell-wall (plasmodia). They multiply by means of spores, which in the true Slime-Fungi[3][6] are produced in sporangia, but in some others[4] free. The spores are round cells (Fig. 1 a) which in all the true Slime-Fungi are surrounded by a cell-wall. The wall bursts on germination, and the contents float out in the water which is necessary for germination. They move about with swimming and hopping motions like swarmspores (e, f), having a cilia at the front end and provided with a cell-nucleus and a pulsating vacuole. Later on they become a little less active, and creep about more slowly, while they continue to alter their form, shooting out arms in various places and drawing them in again (g, h, i, k, l, m); in this stage they are called Myxamœbæ.

Fig. 1.—a-l Development of “Fuligo” from spore to Myxamœba; a-m are magnified 300 times; m is a Myxamœba of Lycogala epidendron; l´ three Myxamœbæ of Physarum album about to unite; o, a small portion of plasmodium, magnified 90 times.

Fig. 2.—The plasmodium (a) of Stemonitis fusca, commencing to form into sporangia (b); drawn on July 9. The dark-brown sporangia were completely formed by the next morning; c-e shows the development of their external form.

Fig. 3.—Four sporangia of Stemonitis fusca, fixed on a branch. a The plasmodium.

Fig. 4.—Sporangium of Arcyria incarnata. B closed; C open; p wall of sporangium; cp capilitium.

The Myxamœba grows whilst taking up nourishment from the material in which it lives, and multiplies by division. At a later stage a larger or smaller number of Myxamœbæ may be seen to[7] coalesce and form large masses of protoplasm, plasmodia, which in the “Flowers of Tan” may attain the size of the palm of a hand, or even larger, but in most others are smaller. The plasmodia are independent, cream-like masses of protoplasm, often containing grains of carbonate of lime and colouring matter (the latter yellow in the Flowers of Tan). They creep about in the decaying matter in which they live, by means of amœboid movements, internal streamings of the protoplasm continually taking place; finally they creep out to the surface, and very often attach themselves to other objects, such as Mosses, and form sporangia (Fig. 2). These are stalked or sessile and are generally cylindrical (Fig. 3), spherical or pear-shaped (Fig. 4); they rarely attain a larger size than that of a pin’s head, and are red, brown, white, blue, yellow, etc., with a very delicate wall. In some genera may be found a “Capillitium” (Fig. 4 cp), or network of branched fine strands between the spores. Flowers of[8] Tan (Fuligo septica) has a fruit-body composed of many sporangia (an Æthalium), which has the appearance of flat, irregular, brown cakes, inside the fragile external layer of which a loose powder, the spores, is found. It generally occurs on heaps of tanners’ bark, and appears sometimes in hot-beds in which that material is used, and is destructive by spreading itself over the young plants and choking them.

All the motile stages may pass into resting stages, the small forms only surrounding themselves with a wall, but the large ones at the same time divide in addition into polyhedral cells. When favourable conditions arise, the walls dissolve and the whole appears again as a naked (free-moving) mass of protoplasm.

To the genuine Slime-Fungi belong: Arcyria, Trichia, Didymium, Physarum, Stemonitis, Lycogala, Fuligo, Spumaria, Reticularia.

Some genera wanting a sporangium-wall belong to the Slime-Fungi: Ceratiomyxa, whose fruit-body consists of polygonal plates, each bearing stalked spores; Dictyostelium, in which the swarm-stage is wanting and which has stalked spores. Plasmodiophora brassicæ preys upon the roots of cabbages and other cruciferous plants, causing large swellings. Pl. alni causes coral-shaped outgrowths on the roots of the Alder (Alnus). Phytomyxa leguminosarum may be found in small knobs (tubercles) on the roots of leguminous plants. It is still uncertain whether it is this Fungus or Bacteria which is the cause of the formation of these tubercles.

Sub-Division II.—ALGÆ.

Mode of Life. The Algæ (except most of the Bacteria) are themselves able to form their organic material by the splitting up of the carbonic acid contained in the water, or air in some cases, and for this purpose need light. The majority live in water, fresh or salt, but many are present on damp soil, stones, bark of trees, etc.

With the exception of the Bacteria, no saprophytes have actually been determined to belong to this group, and only very few true parasites (for instance, Phyllosiphon arisari, Mycoidea, etc.), but a good many are found epiphytic or endophytic on other Algæ, or water plants, and on animals (for instance, certain Schizophyceæ and Protococcoideæ; Trichophilus welckeri in the hairs of Bradypus, the Sloth), and several species in symbiotic relation to various[9] Fungi (species of Lichen), to Sponges (e.g. Trentepohlia spongiophila, Struvea delicatula), and to sundry Infusoria and other lower animals as Radiolarias, Hydra, etc. (the so-called Zoochlorella and Zooxantella, which are perhaps partly stages in development of various Green and Brown Algæ).

Vegetative Organs. The cells in all the Algæ (excepting certain reproductive cells) are surrounded by a membrane which (with the exception of the Bacteria) consists of pure or altered cellulose, sometimes forming a gelatinous covering, at other times a harder one, with deposits of chalk or silica formed in it. The cell-nucleus, which in the Schizophyta is less differentiated, may be one or more (e.g. Hydrodictyon, Siphoneæ) in each cell. Excepting in the majority of the Bacteria, colour materials (of which chlorophyll, or modifications of it, always seems to be found) occur, which either permeate the whole cytoplasm surrounding the cell-nucleus, as in most of the coloured Schizophyta, or are contained in certain specially formed small portions of protoplasm (chromatophores).

The individual at a certain stage of development consists nearly always of only one cell; by its division multicellular individuals may arise, or, if the daughter-cells separate immediately after the division, as in many of the simplest forms, the individual will, during the whole course of its existence, consist of only a single cell (unicellular Algæ). In multicellular individuals the cells may be more or less firmly connected, and all the cells of the individual may be exactly alike, or a division of labour may take place, so that certain cells undertake certain functions, and are constructed accordingly; this may also occur in parts of the cell in the large unicellular and multinuclear Algæ (Siphoneæ, p. 62).

The cells in most of the Algæ belong to the parenchymatous form; these, however, in the course of their growth, may very often become somewhat oblong; in many Algæ (particularly Fucoideæ and Florideæ) occur, moreover, hyphæ-like threads, which are very long, often branched, and are either formed of a single cell, or, more frequently, of a row of cells, having a well-pronounced apical growth. The parenchymatous as well as the hyphæ-like cells may, in the higher Algæ (especially in certain Fucoideæ and Florideæ), be further differentiated, so that they form well-defined anatomico-physiological systems of tissue, i.e. assimilating, conducting, storing, and mechanical.

With regard to the external form, the thallus may present no[10] differentiation, as in many unicellular Algæ, or in multicellular Algæ of the lower order, which are then either equally developed in all directions (e.g. Pleurococcus, Fig. 47), or form flat cell-plates (Merismopedium) or threads (Oscillaria, Fig. 21). The first step in the way of differentiation appears as a difference between apex and base (Rivularia, Porphyra); but the division of labour may proceed so that differences may arise between vegetative and reproductive cells (Œdogonium, Fig. 54); hairs and organs of attachment (rhizoids and haptera), which biologically serve as roots, are developed, and even leaves in certain forms of high order, belonging to different classes (e.g. Caulerpa, Fig. 59; Characeæ, Fig. 61; Sargassum, Fig. 72; and many Florideæ).

The non-sexual reproduction takes place vegetatively, in many instances, simply by division into two, and more or less complete separation of the divisional products (Diatomaceæ, Desmidiaceæ (Fig. 36), many Fission-plants, etc.), or by detached portions of the thallus (e.g. Caulerpa, Ulva lactuca, etc.; among many Schizophyceæ, small filaments known as hormogonia are set free), or asexually by special reproductive cells (spores) set free from the thallus; these may be either stationary or motile. The stationary reproductive cells (spores) may either be devoid of cell-wall (tetraspores of the Florideæ), or may possess a cell-wall; in the latter case they may be formed directly from the vegetative cells, generally by the thickening of the walls (akinetes), or only after a process of re-juvenescence (aplanospores). Aplanospores, as well as akinetes, may either germinate immediately or may become resting-cells, which germinate only after a period of rest.

The motile asexual reproductive cells are spherical, egg- or pear-shaped, naked, swarmspores (zoospores), which have arisen in other cells (zoosporangia), and propel themselves through the water by means of cilia; or they are Phyto-Amœbæ, which have no cilia and creep on a substratum by means of pseudopodia. The cilia, which are formed from the protoplasm (in the Bacteria, however, from the membrane), are mostly situated at the pointed and colourless end, which is directed forwards when in motion, and are 1, 2 (Fig. 5 B), 4 or more. Both the cilia in the Brown Algæ are attached to one side (Fig. 65); they are occasionally situated in a circle round the front end (Œdogonium, Fig. 6 a, and Derbesia), or are very numerous and situated in pairs distributed over a large part or nearly the whole of the zoospore (Vaucheria). Besides being provided with one or more nuclei[11] (Vaucheria), they may also have a red “eye spot” and vacuoles, which are sometimes pulsating, i.e. they appear and reappear at certain intervals. The swarmspores move about in the water in irregular paths, and apparently quite voluntarily, revolving round their longer axes; but they come to the surface of the water in great numbers either because of their dependence on light, or driven by warm currents in the water, or attracted by some passing mass of food material. The swarmspores germinate, each forming a new plant, as their movement ceases they surround themselves with a cell-wall, grow, and then divide; in Fig. 6 b, two may be seen in the condition of germination, and about to attach themselves by means of the front end, which has been developed into haptera (see also Fig. 5 B, lowest figure).

The sexual reproduction here, probably in all cases, consists in the coalescence of two masses of protoplasm, that is, in the fusion of their nuclei.

Fig. 5.—Cladophora glomerata. A The lower cells are full of swarmspores, whilst from the upper one the greater part have escaped through the aperture m. B Free and germinating swarmspores.

Fig. 6.—Œdogonium: a (free), b germinating swarmspores.

Fig. 7.—Zanardinia collaris. A Male gametangia (the small-celled) and female gametangia (large-celled). C Female gamete. D Male gamete. B E Fertilisation. F Zygote. G Germinating zygote.

The simplest and lowest form is termed conjugation, or isogamous fertilisation, and is characterized by the fact that the two coalescing cells (termed gametes) are equal, or almost equal, in shape and size (the female gamete in the Cutleriaceæ, e.g. Zanardinia[12] collaris, Fig. 7, is considerably larger than the male gamete). The cell in which the gametes are developed is called a gametaugium, and the reproductive cell formed by their union—which generally has a thick wall and only germinates after a short period of rest—is termed a zygote or zygospore. The conjugation takes place in two ways:—

(a) In the one way the gametes are motile cells (planogametes, zoogametes, Fig. 8), which unite in pairs during their swarming hither and thither in the water; during this process they lie side by side (Fig. 8 d), generally at first touching at the clear anterior end, and after a time they coalesce and become a motionless zygote, which surrounds itself with a cell-wall (Fig. 8 e). This form of conjugation is found in Ulothrix (Fig. 8 d), Acetabularia, and other Algæ (Figs. 45, 56, 66).

Fig. 8.—Ulothrix zonata: a portion of a thread with zoospores, of which two are formed in each cell (zoosporangium), the dark spots upon them are the “red eye-spots”; 1, 2, 3, 4 depict successive stages in the development of the zoospores; b a single zoospore, at v the pulsating vacuole; c portion of a thread with gametes, of which sixteen are formed in each gametangium; d gametes free and in conjugation; e conjugation has been effected, and the formed zygotes are in the resting condition.

(b) Among other Algæ (e.g. Diatomaceæ and Conjugatæ), the conjugating cells continue to be surrounded by the cell-wall of the mother-cell (aplanogametes in an aplanogametangium); the[13] aplanogametangia generally grow out into short branches, which lie close together and touch one another, the wall at the point of contact is then dissolved (Fig. 39). Through the aperture thus formed, the aplanogametes unite, as in the first instance, and form a rounded zygote, which immediately surrounds itself with a cell-wall. Various modifications occur; compare Figs. 37, 39, 41, 43.

Fig. 9.—Fertilisation in the Bladder-wrack (Fucus vesiculosus).

Fig. 10.—Sphæroplea annulina.

The highest form of the sexual reproduction is the Egg- or Oogamous fertilisation. The two coalescing cells are in the main unlike each other in form as well as size. The one which is considered as the male, and is known as the spermatozoid (antherozoid), developes as a rule in large numbers in each mother-cell (antheridium); they are often self-motile (except in the Florideæ, where they are named spermatia), and are many times smaller than the other kind, the female, which is known as the egg-cell, (oosphere). The egg-cell is always a motionless, spherical, primordial cell which can either float about freely in the water, as in the Fucaceæ (Fig. 9), or is surrounded by a cell-wall (oogonium); generally only one oosphere is to be found in each oogonium, but several occur in Sphæroplea (Fig. 10). The result[14] of the spermatozoid coalescing with the egg-cell is, as in this case, the formation of a oospore, which generally undergoes a period of rest before germination (the Florideæ are an exception, a fruit-body, cystocarp, being produced as the result of coalescence).

The female (parthenogenesis) or male (androgenesis) sexual cell may, sometimes without any preceding fertilisation, form a new individual (e.g. Ulothrix zonata, Cylindrocapsa, etc.).

Systematic division of the Algæ. The Algæ are divided into the following ten classes:

Among the lowest forms of the Algæ, the Syngeneticæ, the Dinoflagellata, and the unicellular Volvocaceæ (Chlamydomoneæ), distinct transitional forms are found approaching the animal kingdom, which can be grouped as animals or plants according to their method of taking food or other characteristics. Only an artificial boundary can therefore be drawn between the animal and vegetable kingdoms. In the following pages only those forms which possess chromatophores, and have no mouth, will be considered as Algæ.

Class 1. Syngeneticæ.

The individuals are uni- or multicellular, free-swimming or motionless. The cells (which in the multicellular forms are loosely connected together, often only by mucilaginous envelopes) are naked or surrounded by a mucilaginous cell-wall, in which silica is never embedded. They contain one cell-nucleus, one or more pulsating[15] vacuoles, and one to two band- or plate-like chromatophores with a brown or yellow colour, and sometimes a pyrenoid.

Reproduction takes place by vegetative division, or asexually by zoospores, akinetes (or aplanospores?). Sexual reproduction is unknown. They are all fresh water forms.

The Syngeneticæ are closely related to certain forms in the animal kingdom, as the Flagellatæ.

Fig. 11.—Syncrypta volvox: the multicellular individual is surrounded by a mucilaginous granular envelope.

Fig. 12.—Chrsopyxis bipes: m envelope, Ec chromatophore, cv contractile vacuole.

Class 2. Dinoflagellata.

The individuals are of a very variable form, but always unicellular, and floating about in free condition. The cell is dorsiventral, bilateral, asymmetric and generally surrounded by a colourless membrane, which has no silica embedded in it, but is formed of a substance allied to cellulose. The membrane, which externally is provided with pores and raised borders, easily breaks up into irregularly-shaped pieces. In the forms which have longitudinal and cross furrows, two cilia are fixed where these cross each other, and project through a cleft in the membrane; one of these cilia projects freely and is directed longitudinally to the front or to the rear, the other one stretches crosswise and lies close to the cell, often in a furrow (cross furrow). The chromatophores are coloured brown or green and may either be two parallel (Exuviella), or several radially placed, discs, which sometimes may coalesce and become a star-shaped chromatophore. The coloring material (pyrrophyl) consists, in addition to a modification of chlorophyl, also of phycopyrrin and peridinin; this colour is sometimes more or less masked by the products of assimilation which consist of yellow, red or colourless oil (?) and starch. Cell-nucleus one: in Polydinida several nuclei are found; contractile vacuoles many, which partly open in the cilia-cleft (Fig. 13 gs). In some an eye-spot, coloured red by hæmatochrome, is found. Pyrenoids occur perhaps in Exuviella and Amphidinium.

The reproduction takes place as far as is known at present, only by division. This, in many salt water forms, may take place in the swarming condition, and, in that case, is always parallel to the longitudinal axis. The daughter-individuals, each of which retains half of the original shell, sometimes do not separate at once from each other, and thus chains (e.g. in Ceratium) of several connected individuals may be formed. In others, the division occurs after the cilia have been thrown off and the cell-contents rounded. The daughter-cells then adopt entirely new cell-walls. A palmella-stage (motionless division-stage) sometimes appears to[17] take place, and also aplanospores (?) with one or two horn-like elongations (e.g. in Peridinium cinctum and P. tabulatum); at germination one, or after division, two or more, new individuals may be formed.

Sexual reproduction has not been observed with certainty.

The Dinoflagellata move forward or backward, turning round their longitudinal axes; in their motion they are influenced by the action of light. The motion possibly may be produced only by the transverse cilium, which vibrates rapidly; whilst the longitudinal cilium moves slowly, and is supposed to serve mainly as a steering apparatus. They live principally in salt water, but also in fresh.

Besides the coloured forms, which are able to make their own organic compounds by the splitting up of the carbonic acid contained in the water, there are a few colourless forms (e.g. Gymnodinium spirale), or such as do not possess chromatophores (Polykrikos); these appear to live saprophytically, and may be able to absorb solid bodies with which they come in contact.

Dinoflagellata occur in the “Plankton” of the open sea, where they form together with Diatomaceæ the basis for the animal life. It is known with certainty that some salt water forms (like the Noctiluca, which belongs to the animal kingdom and to which they are perhaps related) produce light, known as phosphorescence.

Fig. 13.—A and B Glenodinium cinctum. A seen from the ventral side, B from behind; fg transverse cilium; g longitudinal cilium; ch chromatophores; a starch; n cell-nucleus; v vacuole; oc eye-spot; C Ceratium tetraceros from the ventral side; r the right, b the posterior horn; lf longitudinal furrow; gs cilium-cleft; v vacuole; g longitudinal cilium. (A and B mag. 450 times, C 337 times.)

Class 3. Diatomeæ.

The individuals—each known as a frustule—assume very various forms and may be unicellular or multicellular, but present no differentiation; many similar cells may be connected in chains, embedded in mucilaginous masses, or attached to mucilaginous stalks. The cells are bilateral or centric, often asymmetrical, slightly dorsiventral and have no cilia; those living in the free condition have the power of sliding upon a firm substratum. The cell contains 1 cell-nucleus and 1–2 plate-shaped or several disc-shaped chromatophores. The colouring material “Melinophyl” contains, in addition to a modification of chlorophyl, a brown colouring matter, diatomin. 1 or 2 pyrenoids sometimes occur. Starch is wanting and the first product of assimilation appears to be a kind of oil (?).

Fig. 14.—Pinnularia: B, from the edge, shows the valves fitting together; A, a valve.

Fig. 15.—Various Diatomaceæ. A Diatoma vulgare. B Tabellaria flocculosa. C Navicula tumida (lateral views). D Gomphonema constrictum (lateral views). E Navicula west[=i][=i] (lateral views).

The cell-walls are impregnated with silica to such a degree that they are imperishable and are therefore able to contribute in a great measure to the formation of the earth’s crust. The structure of their cell-wall is most peculiar and differs from all other plants (except certain Desmidiaceæ); it does not consist of a single piece but is made up of two—the “shells”—(compare Exuviella and Prorocentrum among the Dinoflagellata) which are fitted into each other, one being a little larger than the other and embracing its edge, like a box with its lid (Fig. 14 B). The two parts which correspond to the bottom and lid of the box are known as valves. Along the central line of the valves a longitudinal rib may often be found, interrupted at its centre by a small cleft (perhaps homologous with the cilia-cleft of the Dinoflagellata), through which the protoplasm is enabled to communicate with the exterior (Fig. 14 A). It is principally by reason of the valves, which bear numerous fine, transverse ribs, striæ or warts, etc. (Figs. 14, 15, 17), that the Diatomeæ have become so well known and employed as test objects in microscopical science. When the division takes place, the two shells are separated a little from each other, and after the cell-contents have divided into two masses, two new shells are formed, one fitting into the larger valve, the other one[19] into the smaller valve of the original frustule. The latter cell (frustule) is thus, upon the whole, smaller than the mother-cell, and as the cells do not increase in size, some frustules are smaller than the ones from which they are derived, and thus, by repeated divisions, it follows that smaller and smaller frustules are produced. This continued diminution in size is, however, compensated for by the formation, when the cells have been reduced to a certain minimum, of auxospores, 2–3 times larger. These may either be formed asexually by the protoplasm of a cell increasing, rounding off and surrounding itself with a new wall (e.g. Melosira) or after conjugation, which may take place with various modifications: 1. Two individuals unite after the secretion of a quantity of mucilage, and the valves then commence to separate from each other, on the side which the two individuals turn towards each other. The protoplasmic bodies now release themselves from their cell-wall, and each rounds off to form an ellipsoidal mass; these two protoplasmic[20] masses (gametes) coalesce to form a zygote, the cell-nuclei and chromatophores also fusing together. The zygote increases in size, and surrounds itself with a firm, smooth, siliceous wall—the perizonium. The auxospores, whichever way they arise, are not resting stages. The germination of the zygote commences by the protoplasm withdrawing itself slightly from the cell-wall and constructing first the larger valve, and later on the smaller one; finally the membrane of the zygote bursts (e.g. Himantidium). 2. The conjugation occurs in a similar manner, but the protoplasm of the cells divides transversely before conjugation into two daughter-cells. Those lying opposite one another conjugate (Fig. 16) and form two zygotes. The formation of the perizonium, and germination take place as in the preceding instance (e.g. Epithemia). 3. Two cells place themselves parallel to each other, and each of the two cell-contents, without coalescing, becomes an auxospore. The formation of the wall takes place as in the preceding case. This is found in the Naviculeæ, Cymbelleæ, the Gomphonemeæ (e.g. Frustulia, Cocconema).

Fig. 16.—Conjugation of Cymbella variabilis. A, The protoplasm in the two cells has divided into two masses; B these masses coalesce in pairs; the cells (B C) enclosed in a mucilaginous matrix. C D Auxospores and their formation.

The Diatomaceæ may be found in salt as well as in fresh water (often in such masses that the colour of the water or mud becomes yellow or brown; in the same manner the genera Chætoceros, Rhizosolenia, Coscinodiscus, and several others, form large slime-masses, “Plankton” on the surface of the sea), on damp soil and in dust blown by the wind. They occur as fossils in the recent formations, often in large deposits (siliceous earth, mountain meal), as in the cement lime in Jutland, the alluvial deposits beneath Berlin, in clay strata beneath peat bogs, in guano, etc.[21] These accumulations of fossilized diatoms are used in the manufacture of dynamite and in various manufactures.

The Diatomaceæ appear nearest to, and must be placed as a group co-ordinate with the Dinoflagellata, as they doubtless may be supposed to derive their origin from forms resembling Exuviella, and to have lost the cilia. The resemblances to the Desmidiaceæ which are striking in many respects, can only be conceived as analogies, and cannot be founded upon homologies, and it is therefore impossible to regard them as proof of genetic relationship. The family contains only one order.

Fig. 17.—Various Diatomeæ. A Synedra radians. B Epithemia turgida (from the two different sides). C Cymbella cuspidata. D Cocconeis pediculus (on the right several situated on a portion of a plant, on the left a single one more highly magnified).

Order 1. Diatomaceæ. This order may be divided into two sub-orders, viz.—

Sub-Order 1. Placochromaticæ. The chromatophores are discoid, large, 1 or 2 in each cell; the structure of the valves is bilateral and always without reticulate markings. The following groups belong to this sub-order: Gomphonemeæ, Cymbelleæ, Amphoreæ, Achnantheæ, Cocconeideæ, Naviculeæ, Amphipleureæ, Plagiotropideæ, Amphitropideæ, Nitzchieæ, Surirayeæ, and Eunotieæ.

Sub-Order 2. Coccochromaticæ. The chromatophores are granular, small and many in each cell. The structure of the cells is zygomorphic or centric, often with reticulate markings. The following groups belong to this sub-order: Fragilarieæ, Meridieæ, Tabellarieæ, Licmophoreæ, Biddulphieæ, Anguliferæ, Eupodisceæ, Coscinodisceæ, and Melosireæ.

[22]

Class 4. Schizophyta, Fission-Algæ.

The individuals are 1—many celled; the thallus consists in many of a single cell, in others of chains of cells, the cells dividing in only one definite direction (Figs. 18, 21). In certain Fission-Algæ the cell-chain branches (Fig. 30) and a difference between the anterior and the posterior ends of the chain is marked; in some, the cells may be united into the form of flat plates by the cell-division taking place in two directions; and in others into somewhat cubical masses, or rounded lumps of a less decided form, by the divisions taking place in three directions; or less defined masses may be formed by the divisions taking place in all possible directions.

The cell-walls rarely contain cellulose, they often swell considerably (Figs. 20, 22), and show distinct stratifications, or they are almost completely changed into a mucilaginous mass in which the protoplasts are embedded, e.g. in Nostoc (Fig. 22), and in the “Zooglœa” stage of the Bacteria (Fig. 27). Sexual reproduction is wanting. Vegetative reproduction by division and the separation of the divisional products by the splitting of the cell-wall or its becoming mucilaginous; among the Nostocaceæ, Lyngbyaceæ, Scytonemaceæ, etc., “Hormogonia” are found; in Chamæsiphon and others single reproductive akinetes are formed. Many Fission-Algæ conclude the growing period by the formation of resting akinetes or aplanospores.

The Schizophyta may be divided into 2 families:

1. Schizophyceæ.

2. Bacteria.

Family 1. Schizophyceæ,[5] Blue-Green Algæ.

All the Blue-green Algæ are able to assimilate carbon by means of a colouring material containing chlorophyll (cyanophyll); but the chlorophyll in this substance is masked by a blue (phycocyan), or red (phycoerythrin, e.g. in Trichodesmium erythræum in the Red Sea) colouring matter which may be extracted from them in cold water after death. The colouring matter, in most of them, permeates the whole of the protoplasm (excepting the cell-nucleus), but in a few (e.g. Glaucocystis, Phragmonema), slightly developed chromatophores are to be found. Where the cells are united into filaments (cell-chains) a differentiation into apex and base (Rivulariaceæ) may take place, and also between ordinary vegetative cells and heterocysts; these latter cannot divide, and are distinguished[23] from the ordinary vegetative cells (Fig. 22 h) by their larger size, yellow colour, and poverty of contents. Branching sometimes occurs and is either true or spurious.

Fig. 18.—Microcoleus lyngbyanus: a portion of a filament, the thick sheath encloses only one cell-chain; in one place a cell is drawn out by the movement of the cell-chain; b the cell-chain has divided into two parts (“hormongonia”) which commence to separate from each other.

The cell-chain in the spurious branching divides into two parts, of which either one or both grow beyond the place of division (Fig. 18) and often out to both sides (e.g. Scytonema), the divisions however, always take place transversely to the longitudinal direction of the cell-chain. In the true branching a cell elongates in the direction transverse to the cell-chain, and the division then takes place nearly at right angles to the former direction (Sirosiphoniaceæ).

Fig. 19.—Cylindrospermum majus: a resting akinete with heterocyst; b-d germinating stages of a resting akinete; e filament with two heterocysts and the formation of new akinetes; f part of a filament with a heterocyst, and mature resting akinete.

Cilia are wanting, but the filaments are sometimes self-motile (e.g. hormogonia in Nostoc) and many partly turn round their axes, partly slide forward or backward (Oscillaria).

Reproduction takes place by spores and hormogonia in addition[24] to simple cell-division. Hormogonia are peculiar fragments of a cell-chain capable of motion, and often exhibit a vigorous motion in the sheath, until at last they escape and grow into a new individual (Fig. 18). The spores are reproductive akinetes (Chamæsiphon, etc.) or resting akinetes; these latter arise by the vegetative cells enlarging and constructing a thick cell-wall (Fig. 19 e f). On germination, this cell-wall bursts and the new cell-chain elongates in the same longitudinal direction as before (Fig. 19 b c). Many (e.g. Oscillaria) may however winter in their ordinary vegetative stage. Aplanospores are wanting.

The Fission-Algæ are very prevalent in fresh water and on damp soil, less so in salt water; they also often occur in water which abounds in decaying matter. Some are found in warm springs with a temperature as high as 50° C.

The Family may be divided into 2 sub-families:

1. Homocysteæ (heterocysts are wanting): Chroococcaceæ, Lyngbyaceæ and Chamœsiphonaceæ.

2. Heterocysteæ (heterocysts present): Nostocaceæ, Rivulariaceæ, Scytonemaceæ and Sirosiphoniaceæ.

Order 1. Chroococcaceæ. The individuals are 1—many-celled, but all the cells are uniform, united to form plates or irregular masses, often surrounded by a mucilaginous cell-wall, but never forming cell-chains. Multiplication by division and sometimes by resting akinetes, but reproductive akinetes are wanting. Chroococcus, Aphanocapsa, Glœocapsa (Fig. 20), Cœlosphærium, Merismopedium, Glaucocystis, Oncobyrsa, Polycystis, Gomphosphæria.

Fig. 20.—Glœocapsa atrata: A, B, C, D, E various stages of development.

Fig. 21.—Oscillaria; a terminal, b central portion of a filament.

Order 2. Lyngbyaceæ (Oscillariaceæ). The cells are discoid (Fig. 21), united to straight or spirally twisted, free filaments, which are unbranched, or with spurious branching. The ends of the cell-chains are similar. Heterocysts absent. Reproduction by synakinetes, resting akinetes are wanting. Oscillaria (Fig. 21), Spirulina, Lyngbya, Microcoleus, Symploca, Plectonema.

[25]

Order 3. Chamæsiphonaceæ. The individuals are 1—many-celled, attached, unbranched filaments with differentiation into apex and base, without heterocysts. Multiplication by reproductive akinetes; resting akinetes are wanting. Dermocarpa, Clastidium, Chamæsiphon, Godlewskia, Phragmonema.

Order 4. Nostocaceæ. The individuals are formed of multicellular, unbranched filaments, without differentiation into apex and base; heterocysts present. Reproduction by synakinetes and resting akinetes.

Fig. 22.—Nostoc verrucosum. A The plant in its natural size; an irregularly folded jelly-like mass. B One of the cell-chains enlarged, with its heterocysts (h), embedded in its mucilaginous sheath.

Some genera are not mucilaginous, e.g. Cylindrospermum (Fig. 19). The cell-chains in others, e.g. Nostoc, wind in between one another and are embedded in large structureless jelly-like masses, which may attain the size of a plum or even larger (Fig. 22); sometimes they are found floating in the water, sometimes attached to other bodies. Other genera as follows: Aphanizomenon and Anabæna (in lakes and smaller pieces of water); Nodularia is partly pelagic. Some occur in the intercellular spaces of higher plants, thus Nostoc-forms are found in Anthoceros, Blasia, Sphagnum, Lemna, and in the roots of Cycas and Gunnera; Anabæna in Azolla.

Order 5. Rivulariaceæ. The individuals are multicellular filaments, with differentiation into apex and base; spurious branching, and a heterocyst at the base of each filament, reproduction by synakinetes and resting akinetes, rarely by simple reproductive akinetes. Rivularia, Glœotrichia, Isactis, Calothrix.

Order 6. Scytonemaceæ. The individuals are formed of multicellular filaments with no longitudinal division; differentiation into apex and base very slight or altogether absent;[26] branching spurious; heterocysts present. Reproduction by synakinetes, rarely by resting akinetes and ordinary reproductive akinetes. Tolypothrix, Scytonema, Hassalia, Microchæte.

Order 7. Sirosiphoniaceæ. The individuals are formed of multicellular threads with longitudinal divisions; true branching and heterocysts, and often distinct differentiation into apex and base. Reproduction by synakinetes, rarely by resting akinetes and ordinary reproductive akinetes. Hapalosiphon, Stigonema, Capsosira, Nostocopsis, Mastigocoleus.

Family 2. Bacteria.[6]

The Bacteria (also known as Schizomycetes, and Fission-Fungi) are the smallest known organisms, and form a parallel group to the Blue-green Algæ, but separated from these Algæ by the absence of their colouring material; chlorophyll is only found in a few Bacteria.

The various forms under which the vegetative condition of the Bacteria appear, are termed as follows:

1. Globular forms, cocci (Figs. 27, 30 c): spherical or ellipsoidal, single cells, which, however, are usually loosely massed together and generally termed “Micrococci.”

2. Rod-like forms: more or less elongated bodies; the shorter forms have been styled “Bacterium” (in the narrower sense of the word), and the term “Bacillus” has been applied to longer forms which are straight and cylindrical (Figs. 28, 29, 30 E).

Fig. 23.—Spirillum sanguineum. Four specimens. One has two cilia at the same end, the sulphur grains are seen internally.

3. Thread-like forms: unbranched, long, round filaments, resembling those of Oscillaria, are possessed by Leptothrix (very thin, non-granular filaments; Fig. 30 A, the small filaments) and Beggiatoa (thicker filaments, with strong, refractile grains or drops of sulphur (Fig. 31); [27]often self-motile). Branched filaments, with false branching like many Scytonemaceæ, are found in Cladothrix (Fig. 30 B, G).

4. Spiral forms: Rod-like or filamentous bodies, which more or less strongly resemble a corkscrew with a spiral rising to the left. In general these are termed Spirilla (Fig. 23); very attenuated spirals, Vibriones (standing next to Fig. 30 M); if the filaments are slender and flexible with a closely wound spiral, Spirochætæ (Fig. 24).

5. The Merismopedium-form, consisting of rounded cells arranged in one plane, generally in groups of four, and produced by divisions perpendicular to each other.

6. The Sarcina-form, consisting of roundish cells which are produced by cellular division in all the three directions of space, united into globular or ovoid masses (“parcels”) e.g. Sarcina ventriculi (Figs. 25, 26).

Fig. 24.—Spirochæte obermeieri, in active motion (b) and shortly before the termination of the fever (c); a blood corpuscles.

All Bacteria are unicellular. In the case of the micrococci this is self-evident, but in the “rod,” “thread,” and “spiral” Bacteria, very often numerous cells remain united together and their individual elements can only be recognised by the use of special reagents.

Fig. 25.—Sarcina ventriculi. One surface only is generally seen. Those cells which are drawn with double contour are seen with the correct focus, and more distinctly than those cells lying deeper drawn with single contour.

Fig. 26.—Sarcina minuta: a-d successive stages of one individual (from 4–10 p.m.); f an individual of 32 cells.

The condition termed “Zooglœa,” which reminds us of Nostoc, is produced by the cells becoming strongly mucilaginous. A number of individuals in active division are found embedded in a mass of mucilage, which either contains only one, or sometimes more, of[28] the above-named forms. The individuals may eventually swarm out and continue their development in an isolated condition. Such mucilaginous masses occur especially upon moist vegetables (potatoes, etc.), on the surface of fluids with decaying raw or cooked materials, etc. The mucilaginous envelope is thrown into folds when the Bacteria, with their mucilaginous cell-walls, multiply so rapidly that there is no more room on the surface of the fluid.

The cells of the Bacteria are constructed like other plant-cells in so far as their diminutive size has allowed us to observe them. The cell-wall only exceptionally shows the reactions of cellulose (in Sarcina, Leuconostoc; also in a Vinegar-bacterium, Bacterium xylinum); a mucilaginous external layer is always present. The body of the cell mostly appears to be an uniform or finely granulated protoplasm. Very few species (e.g. Bacillus virens) contain chlorophyll; others are coloured red (purple sulphur Bacteria); the majority are colourless. Bacillus amylobacter shows a reaction of a starch-like material when treated with iodine before the spore-formation. Some Bacteria contain sulphur (see p. 37). The body, which has been described as a cell-nucleus, is still of a doubtful nature.

Artificial colourings with aniline dyes (especially methyl-violet, gentian-violet, methylene-blue, fuchsin, Bismarck-brown and Vesuvin) play an important part in the investigations of Bacteria.

Movement. Many Bacteria are self-motile; the long filaments of Beggiatoa exhibit movements resembling those of Oscillaria. In many motile forms the presence of cilia or flagella has been proved by the use of stains; many forms have one, others several cilia attached at one or both ends (Fig. 23) or distributed irregularly over the whole body; the cilia are apparently elongations of the mucilaginous covering and not, as in the other Algæ of the protoplasm. In Spirochæte the movement is produced by the flexibility of the cell itself. Generally speaking, the motion resembles that of swarm-cells (i.e. rotation round the long axis and movement in irregular paths); but either end has an equal power of proceeding forwards.

Vegetative reproduction takes place by continued transverse[29] division; hence the name “Fission-Fungi” or “Fission-Algæ,” has been applied to the Bacteria.

Spores. The spores are probably developed in two ways. In the ENDOSPOROUS species (Figs. 28, 29), the spore arises as a new cell inside the mother-cell. The spores are strongly refractile, smaller than the mother-cell, and may be compared to the aplanospores of other Algæ. In addition to these there are the ARTHROSPOROUS species in which the cells, just as in Nostoc and other Blue-green Algæ, assume the properties of spores without previously undergoing an endogenous new construction, and are able to germinate and form new vegetative generations (Fig. 27). The formation of spores very often commences when the vegetative development begins to be restricted.

Fig. 27.—Leuconostoc mesenterioides: a a zooglœa, natural size; b cross section of zooglœa; c filaments with spores; d mature spores; e-i successive stages of germination; in e portions of the ruptured spore-wall are seen on the external side of the mucilaginous covering. (b-i magnified 520.)

The spores germinate as in Nostoc by the bursting of the external layer of the cell-wall, either by a transverse or longitudinal cleft, but always in the same way, in the same species (Fig. 28, example of transverse cleft).

Distribution. Bacteria and their germs capable of development, are found everywhere, in the air (dust), in surface water, and in the superficial layers of the soil. The number varies very much in accordance with the nature of the place, season, etc. They enter, together with air and food, into healthy animals and occur always in their alimentary tract.

[30]

Growth and reproduction depend upon the conditions of temperature. There is a certain minimum, optimum and maximum for each species; for instance (in degrees Centigrade)—

Fig. 28.—Bacillus megaterium: a outline of a living, vegetative cell-rod; b a living, motile, pair of rods; p a similar 4-celled rod after the effects of iodine alcohol; c a 5-celled rod in the first stages of spore-formation; d-f successive stages of spore-formation in one and the same pair of rods (in the course of an afternoon); r a rod with mature spores; g¹–g³ three stages of a 5-celled rod, with spores sown in nutritive solution; h¹–h², i, k, l stages of germination; m a rod in the act of transverse division, grown out from a spore which had been sown eight hours previously. (After de Bary; a mag. 250, the other figures 600 times).

Fig. 29.—Bacillus amylobacter. Motile rods, partly cylindrical and without spores, partly swollen into various special shapes and with spore-formation in the swelling. s Mature spore, with thick mucilaginous envelope. (After de Bary; mag. 600 times, with the exception of s, which is more highly magnified.)

The functions of life cease on a slight excess of the maximum or minimum temperature, numbness setting in when either of these limits is passed. Crenothrix-threads provided with mucilaginous envelopes may, according to Zopf, sustain a temperature of-10°. Some Bacteria are said to be able to resist the exposure to as low a temperature as-110° for a short time. It is not known at what degree of cold the death of the Bacteria occurs: the greatest degree of heat which the vegetative cells can[31] withstand is about the same as that for other vegetative plant-cells, namely, about 50–60° C. Certain Bacteria, e.g. B. thermophilus, grow and thrive vigorously at 70° C. Many spores, on the contrary, are able to bear far higher temperatures (in several species a temperature for some duration of above 100°, those of Bacillus subtilis, for instance, can withstand for hours a temperature of 100° in nutrient solutions; the spores remain capable of development after exposure to a dry heat of 123° C.).

The Desiccation of the air, if prolonged, kills many forms when in the vegetative condition. The spores however can bear a much longer period of dryness, some even several years.

Oxygen. Some species cannot live without a supply of free oxygen (Aerobic), e.g. the Vinegar-bacteria, the Hay-bacilli, the Anthrax-bacilli, the Cholera-Microspira. Other species again thrive vigorously without supply of free oxygen, and are even checked in their development by the admission of air (Anaerobic), e.g. the butyric acid Bacterium (Clostridium butyricium = Bacillus amylobacter). A distinction may be drawn between obligate and facultative aerobics and obligate and facultative anaerobics. Several Bacteria, producing fermentation, may grow without the aid of oxygen when they are living in a solution in which they can produce fermentation; but, if this is not the case, they can only grow when a supply of oxygen is available. A great number of the pathogenic Bacteria belong to the facultative anaerobics.

A luminous Bacterium (Bacillus phosphorescens) which in the presence of a supply of oxygen gives a bluish-white light, has been found in sea-water. Phosphorescent Bacteria have frequently been observed upon decaying sea-fish, as well as on the flesh of other animals; by transferring the Bacteria from cod fish to beef, etc., the latter may be made luminous.

Organic carbon compounds are indispensable for all Bacteria, (except, as it appears, for the nitrifying organisms), as they can only obtain the necessary supplies of carbon from this source. The supplies of nitrogen, which also they cannot do without, can be obtained equally as well from organic compounds as from inorganic salts, such as saltpetre or ammonia-compounds. The various “ash-constituents” are also essential for their nourishment.

While Moulds and Yeast-Fungi grow best in an acid substratum, the Bacteria, on the other hand, generally thrive best in a neutral or slightly alkaline one.

[32]

In sterilization, disinfection, and antisepsis, means are employed by which the Bacteria are killed, or checked in their development, for instance, by heat (ignition, cooking, hot vapours, hot air, etc.), or poisons (acids, corrosive sublimate). The process of preserving articles of food, in which they are boiled and then hermetically sealed, aims at destroying the Bacteria, or the spores of those which already may be present in them, and excluding all others.

As the Bacteria are unable to assimilate carbon from the carbonic acid of the air, but must obtain it from the carbon-compounds already in existence in the organic world, they are either saprophytes or parasites. Some are exclusively either the one or the other, obligate saprophytes or parasites. But there are transitional forms among them, some of which are at ordinary times saprophytes, but may, when occasion offers, complete their development wholly or partly as parasites—facultative parasites; others are generally parasitic, but may also pass certain stages of development as saprophytes—facultative saprophytes.

All chlorophyll-free organisms act in a transforming and disturbing manner on the organic compounds from which they obtain their nourishment, and while they themselves grow and multiply, they produce, each after its kind, compounds of a less degree of complexity, i.e. they produce fermentation, putrefaction, sometimes the formation of poisons, and in living beings often disease.

Those organisms which produce fermentation are called ferments; this word, however, is also employed for similar transformations in purely chemical materials (inorganic ferments or enzymes). Many organic (“living”) ferments, among which are Yeast-cells and Bacteria, give off during their development certain inorganic and soluble ferments (enzymes) which may produce other transformations without themselves being changed. Different organisms may produce in the same substratum different kinds of transformation; alcoholic fermentation may for instance be produced by different species of Fungi, but in different proportions, and the same species produces in different substrata, different transformations (e.g. the Vinegar-bacteria oxydize diluted alcohol to vinegar, and eventually to carbonic acid and water).

It has not so far been possible to establish a classification of the Bacteria, as the life-history of many species, has not yet been sufficiently investigated.[7] The opinions of botanists are at variance, in many cases, about the forms of growth of a particular kind. Some species are pleomorphic (many-formed) while others possess only one form.

The following Bacteria are Saprophytes:—

Cladothrix dichotoma is common in stagnant and running water which is impregnated with organic matter; the cell-chains have false branching. According to Zopf, Leptothrix ochracea is one of the forms of this species which, in water containing ferrous iron (e.g. as FeCO₃), regularly embeds ferric-oxide in its sheath by means of the activity of the protoplasm. Leptothrix ochracea and other Iron-bacteria, according to Winogradsky (1888), do not continue their growth in water free from protoxide of iron; while they multiply enormously in water which contains this salt of iron. The large masses of ochre-coloured slime, found in meadows, bogs, and lakes, are probably due to the activity of the Iron-bacteria.

Fig. 30.—Cladothrix dichotoma.

Those forms which, according to Zopf’s views, represent the forms of development of Cladothrix dichotoma are placed together in Fig. 30. A represents a group of plants, seventy times magnified, attached to a Vaucheria. The largest one is branched like a tree, with branches of ordinary form; a specimen with spirally twisted branches is seen to the right of the figure, at the lower part some small Leptothrix-like forms. B shows the[34] manner of branching and an incipient Coccus-formation. C a Coccus-mass whose exit from the sheath has been observed. D the same mass as C after the course of a day, the Cocci having turned into rods. E a group of Cocci in which some have developed into shorter or longer rods. F one of these rods before[35] and after treatment with picric acid, which causes the chain-like structure to become apparent. G a portion of a plant with conspicuous sheath, two lateral branches are being formed. H part of a plant, whose cells have divided and form Cocci. The original form of the cells in which the Cocci are embedded may still be recognised. I. Leptothrix-filaments with conspicuous mucilaginous sheath, from which a series of rods is about to emerge; the rod near the bottom is dead, and has remained lying in the sheath. K part of a plant which is forming Cocci, those at the top are in the zooglœa-stage, at the base they are elongating to form rods and Leptothrix-filaments. L a portion of a branched Cladothrix, which divides into motile Bacillus-forms; the rays at the free ends indicate the currents which the cilia produce in the water. M a spirally-twisted, swarming filament, before and after division into halves. N part of a tree-like zooglœa with Cocci and short rods.—All of these spirilla, zooglœa, etc., which Zopf has connected with Clad. dichotoma, are according to Winogradsky, independent organisms.

Micrococcus ureæ produces urinal fermentation (transformation of urinal matter into ammonium carbonate); aerobic; round cells generally united to form bent chains or a zooglœa.—Several other kinds of Bacteria have the same action as this one: in damp soil containing ammonia-compounds, saltpetre-formations are produced by M. nitrificans and several different kinds of Bacteria.

Micrococcus prodigiosus is found on articles of food containing starch; “bleeding bread” is caused by this Bacterium, which has the power of forming a red pigment; it also occurs in milk, and produces lactic acid.

Leuconostoc mesenterioides is the frog-spawn Bacterium (Fig. 27) which is found in sugar manufactories, and has the power of producing a viscous fermentation in saccharine solutions which have been derived from plants, e.g. in beetroot-sugar manufactories, where large accumulations of mucilage are formed at the expense of the sugar, with an evolution of carbonic acid. The cell-rows, resembling somewhat a pearl necklace, have thick mucilaginous cell-walls, and form white “Nostoc”-lumps. The mucilage eventually deliquesces and the cells separate from each other; arthrospores?—Similar viscous deteriorations occur in beer and wine, which may then be drawn out into long, string like filaments—“ropiness.”

Bacterium aceti, the Vinegar-bacterium, oxidizes alcohol into[36] acetic acid (acetous-fermentation) and forms a greyish covering of Bacteria (“Vinegar-mother”) on the surface of the liquid; the acetic acid formed, becomes by continued oxidization by B. aceti, again transformed into carbonic acid and water. Aerobic; short cylindrical cells, often united into chains, or to form a zooglœa; sometimes also rod-and spindle-shaped. The Vinegar-bacteria and other kinds with ball- or rod-forms sometimes become swollen, spindle-shaped, or oval links; they are supposed to be diseased forms[8] (“Involution-forms”).

Bacillus lacticus (Bacterium acidi lactici, Zopf) is always found in milk which has stood for some time, and in sour foods (cabbage, cucumbers, etc.); it turns the milk sour by producing lactic acid fermentation in the sugar contained in the milk; the lactic acid formed, eventually causes the coagulation of the casein. It resembles the Vinegar-bacteria, occurring as small cylindrical cells, rarely in short rows; not self-motile.—Several other Bacteria appear to act in the same way, some occurring in the mouth of human beings; some of these Bacteria give to butter its taste and flavour.

The kefir-grains which are added to milk for the preparation of kefir, contain in large numbers a Bacterium (Dispora caucasica) in the zooglœa-form, a Yeast-fungus, and Bacillus lacticus. Kefir is a somewhat alcoholic sour milk, rich in carbonic acid; it is a beverage manufactured by the inhabitants of the Caucasus, from the milk of cows, goats, or sheep, and is sometimes used as a medicine. In the production of kefir, lactic acid fermentation takes place in one part of the sugar contained in the milk, and alcoholic fermentation in another part, and the casein which had become curdled is partially liquefied (peptonised) by an enzyme of a Zooglœa-bacterium.

Bacillus amylobacter (Bacillus butyricus), the Butyric-acid-bacterium (Fig. 29), is a very common anaerobic which produces fermentation in sugar and lactic-acid salts, and whose principal product is butyric acid. It destroys articles of food and (together with other species) plays a part in the butyric acid fermentation which is necessary in the making of cheese; it is very active wherever portions of plants are decaying, in destroying the cellulose in the cell-walls of herbaceous plants, and is thus useful in the preparation of flax and hemp. The cells are self-motile, generally cylindrical, sometimes united into short rows; endosporous;[37] the spore-forming cells swell, assume very different forms, and show granulose reaction. The germ-tube grows out in the direction of the long axis of the spore.

Bacillus subtilis, the Hay-bacillus, is developed in all decoctions of hay; a slender, aerobic, self-motile Bacillus; endosporous (aplanospores); the spore-wall ruptures transversely on germination.

Crenothrix kuehniana occurs in the springs of many baths, in wells, in water or drain-pipes.

Fig. 31.—Beggiatoa alba: a from a fluid containing abundance of sulphuretted hydrogen; b after lying 24 hours in a solution devoid of sulphuretted hydrogen; c after lying an additional 48 hours in a solution devoid of sulphuretted hydrogen, by this means the transverse walls and vacuoles have become visible.

Beggiatoa (parallel with the Blue-green Alga Oscillaria). Long filaments formed of cylindrical cells which are attached by one of the ends, but which are nearly always free when observed. The filaments, like those of Oscillaria, describe conical figures in their revolutions, the free filaments slide upwards and parallel with one another; sheaths are wanting; strongly refractive sulphur drops are found in the interior. The Beggiatoas are the most prevalent Sulphur-bacteria. They occur, very commonly in large numbers, wherever plant or animal remains are decaying in water in which sulphuretted hydrogen is being formed; thus, for example, B. alba (Fig. 31) occurs frequently as a white covering or slimy film on mud containing organic remains. B. mirabilis is remarkable for its size and its strong peristaltic movements. The Sulphur-bacteria oxidize the sulphuretted hydrogen, and accumulate sulphur in the shape of small granules of soft amorphic sulphur, which in the living cell never passes over into the crystalline state. They next oxidize this sulphur into sulphuric acid, which is immediately rendered neutral by absorbed salts of calcium, and is given off in the form of a sulphate, thus CaCO₃ is principally changed into CaSO₄. In the absence of sulphur the nutritive processes are suspended, and consequently death occurs either sooner or later. The Sulphur-bacteria may exist and multiply in a fluid which only contains traces of organic matter, in which organisms devoid of chlorophyll are not able to exist. The Beggiatoas very frequently form white, bulky masses in sulphur wells and[38] in salt water, the traces of organic material which the sulphur water contains proving sufficient for them. The cellulose-fermentation, to which the sulphur wells in all probability owe their origin, mainly procures them suitable conditions for existence. The CaCO₃ and H₂S, formed during the cellulose fermentation by the reduction of CaSO₄ is again changed into CaSO₄ and CO₂ by the Sulphur-bacteria (Winogradsky, 1887).—Other Sulphur-bacteria, the so-called purple Sulphur-bacteria, e.g. B. roseo-persicina, Spirillum sanguineum (Fig. 23), Bacterium sulfuratum, etc., have their protoplasm mixed with a red colouring matter (bacterio-purpurin) which, like chlorophyll, has the power, in the presence of light, of giving off oxygen (as proved by T. W. Englemann, 1888, in oxygen-sensitive Bacteria). The three purple Sulphur-bacteria mentioned, are, according to Winogradsky, not pleomorphic kinds but embrace numerous species.

Many Spirilli (Spirillum tenue, S. undula, S. plicatile, and others) are found prevalent in decaying liquids.

Bacteria (especially Bacilli) are the cause of many substances emitting a foul odour, and of various changes in milk.

Parasitic Bacteria live in other living organisms; but the relation between “host” and parasite may vary in considerable degree. Some parasites do no injury to their host, others produce dangerous contagious diseases; some choose only a special kind as host, others again live equally well in many different ones. There are further specific and individual differences with regard to the predisposition of the host, and every individual has not the same receptivity at all times.

The harmless parasites of human beings. Several of the above mentioned saprophytes may also occur in the alimentary canal of human beings; e.g., the Hay-bacillus, the Butyric-acid-bacillus, etc.; but the gastric juice prevents the development of others, at all events in their vegetative condition. Sarcina ventriculi, “packet-bacterium,” is only known to occur in the stomach and intestines of human beings, and makes its appearance in certain diseases of the stomach (dilation of the stomach, etc.) in great numbers, without, however, being the cause of the disease. It occurs in somewhat cubical masses of roundish cells (Fig. 25).

Less dangerous parasites. In the mouth, especially between and on the teeth, a great many Bacteria are to be found (more than fifty species are known), e.g. Leptothrix buccalis (long, brittle, very thin filaments which are united into bundles), Micrococci in large lumps, Spirochæte cohnii, etc. Some of them are known to be injurious, as they contribute in various ways to the decay of the teeth (caries dentium); a Micrococcus, for instance, forms lactic acid[39] in materials containing sugar and starch, and the acid dissolves the lime salts in the external layers of the teeth: those parts of the teeth thus deprived of lime are attacked by other Bacteria, and become dissolved. Inflammation in the tissues at the root of a tooth, is probably produced by septic materials which have been formed by Bacteria in the root-canal.

Dangerous Parasites. In a large number of the infectious diseases of human beings and animals, it has been possible to prove that parasitic Bacteria have been the cause of the disease. Various pathogenic Bacteria of this nature, belonging to the coccus, rod, and spiral Bacteria groups, are mentioned in the following:—

Pathogenic Micrococci. Staphylococcus pyogenes aureus produces abscesses of various natures (boils, suppurative processes in internal organs). The same effects are produced by—

Streptococcus pyogenes, which is the most frequent cause of malignant puerperal fever; it is perhaps identical with—

Streptococcus erysipelatis, which is the cause of erysipelas in human beings.

Diplococcus pneumoniæ (A. Fränkel) is the cause of pneumonia, and of the epidemic cerebro-spinal meningitis.

Gonococcus (Neisser) is the cause of gonorrhea and inflammation of the eyes.

Pathogenic Rod-Bacteria. Bacterium choleræ gallinarum, an aerobic, facultative parasite which produces fowl-cholera among poultry; it is easily cultivated on various substrata as a saprophyte. The disease may be conveyed both through wounds and by food, and may also be communicated to mammals.

Bacillus anthracis, the Anthrax bacillus (Fig. 32), chiefly attacks mammals, especially herbivorous animals (house mice, guinea-pigs, rabbits, sheep, cattle), in a less degree omnivorous animals (including human beings), and in a still less degree the Carnivores. Aerobic. Cylindrical cells, 3–4 times as long as broad, united into long rod-like bodies, which may elongate into long, bent, and twisted filaments. Not self-motile. Endosporous. Germination takes place without the throwing off of any spore-membrane (compare Hay-bacillus p. 37 which resembles it). Contagion may take place both by introduction into wounds, and from the mucous membrane of the intestines or lungs, both by vegetative cells and by spores; in intestinal anthrax, however, only by spores. The Bacillus multiplies as soon as it has entered the blood, and the anthrax disease commences. The Bacilli not only give off poison,[40] but also deprive the blood of its oxygen. Vegetative cells only occur in living animals. This species is a facultative parasite which in the first stage is a saprophyte, and only in this condition forms spores.

Fig. 32.—Anthrax bacillus (Bacillus anthracis) with red (b) and white (a) blood-corpuscles.

Fig. 33.—Anthrax bacillus. The formation of the spores; magnified 450 times.

Bacillus tuberculosis produces tuberculosis in human beings, also in domestic animals (perlsucht). It is a distinct parasite, but may also live saprophytically. It is rod-formed, often slightly bent, and is recognised principally by its action with stains (when stained with an alkaline solution of methyl-blue or carbolic fuchsin, it retains the colour for a long time even in solutions of mineral acids, in contrast with the majority of well-known Bacteria): it probably forms spores which are able to resist heat, dryness, etc.

Pathogenic Spiral Bacteria. Spirochæte obermeieri (Fig. 24) produces intermittent fever (febris recurrens); it makes its appearance in the blood during the attacks of fever, but it is not to be found during intervals when there is no fever. Obligate parasite.

Spirillum choleræ asiaticæ (Microspira comma) without doubt produces Asiatic cholera; an exceedingly motile spirillum, which is also found in short, bent rods (known as the “Comma-bacillus”),[41] it lives in the intestines of those attacked by the disease, and gives off a strong poison which enters the body. It is easily cultivated as a saprophyte.

A great many circumstances seem to show that a number of other infectious diseases (syphilis, small-pox, scarlet-fever, measles, yellow-fever, etc.) owe their origin to parasitic Bacteria, but this has not been proved with certainty in all cases.

It has been possible by means of special cultivations (ample supply of oxygen, high temperature, antiseptic materials) to produce from the parasitic Bacteria described above (e.g. the fowl-cholera and the anthrax Bacteria) physiological varieties which are distinct from those appearing in nature and possess a less degree of “virulence,” i.e. produce fever and less dangerous symptoms in those animals which are inoculated with them. The production of such physiological varieties has come to be of great practical importance from the fact that they are used as vaccines, i.e. these harmless species produce in the animals inoculated with them immunity from the malignant infectious Bacteria from which they were derived. This immunity is effected by the change of the products of one or more of the Bacteria, but we do not yet know anything about the way in which they act on the animal organism. The white blood corpuscles, according to the Metschnikoff, play the part of “Phagocytes” by absorbing and destroying the less virulent Bacteria which have entered the blood, and by so doing they are gradually enabled to overcome those of a more virulent nature.

Fig. 34.—a and b The same blood-cell of a Frog: a in the act of engulfing an anthrax-bacillus; b after an interval of a few minutes when the bacillus has been absorbed.

Class 5. Conjugatæ.

The Algæ belonging to this class have chlorophyll, and pyrenoids round which starch is formed. The cells divide only in one direction, they live solitarily, or united to form filaments which generally float freely (seldom attached). Swarm-cells are wanting. The fertilisation is isogamous (conjugation) and takes place by means of aplanogametes. The zygote, after a period of rest, produces, immediately on germination, one or more new vegetative[42] individuals; sometimes akinetes or aplanospores are formed in addition. They only occur in fresh or slightly brackish water.

Order 1. Desmidiaceæ. The cells generally present markings on the outer wall, and are mostly divided into two symmetrical halves by a constriction in the middle, or there is at least a symmetrical division of the protoplasmic cell-contents. The cell-wall consists nearly always of two layers, the one overlapping the other (Fig. 35 C). The cells either live solitarily or are united into unbranched filaments. The mass of protoplasm formed by the fusion of the two conjugating cells becomes the zygote, which on germination produces one (or after division 2, 4 or 8) new vegetative individual. The chromatophores are either star-, plate-, or band-shaped, and regularly arranged round the long axis of the cell.

Fig. 35.—A Cell of Gymnozyga brebissonii, external view showing the distribution of the pores. B A portion of the membrane of Staurastrum bicorne with pores containing protoplasmic projections. C Cell-wall of Hyalotheca mucosa during cell-division: the central part, being already formed, shows the connection with the divisional wall.

The Desmidiaceæ are not able to swim independently, many species, however, show movements of different kinds by rising and sliding forward on the substratum. These movements, which are partly dependent upon, and partly independent of light and the force of gravitation, are connected with the protrusion of a mucilaginous stalk. The mucilage, which sometimes surrounds the whole individual, may acquire a prismatic structure, it is secreted by the protoplasmic threads which project through certain pores definitely situated in the walls (Fig. 35 A, B).

Vegetative multiplication takes places by division. A good example of this is found in Cosmarium botrytis (Fig. 36 A-D). The nucleus and chromatophores divide, and simultaneously the central indentation becomes deeper, the outer wall is then ruptured making a circular aperture through which the inner wall protrudes forming a short, cylindrical canal between the two halves to which it is attached (Fig. 36 C). After elongation the canal is divided by a central transverse wall, which commences as a ring round its[43] inner surface and gradually forms a complete septum. The dividing wall gradually splits, and the two individuals separate from each other, each one having an old and a new half. The two daughter-cells bulge out, receive a supply of contents from the parent-cells, and gradually attain their mature size and development (Fig. 36 B-D). Exceptions to this occur in some forms.

Fig. 36.—Cosmarium botrytis. A-D Different stages of cell-division.

Fig. 37.—Cosmarium meneghinii: a-c same individual seen from the side, from the end, and from the edge; d-f stages of conjugation; g-i germination of the zygote.

Conjugation takes place in the simplest way in Mesotænium, where the two conjugating cells unite by a short tube (conjugation-canal), which is not developed at any particular point. The aplanogametes merge together after the dissolution of the dividing wall, like two drops of water, almost without any trace of preceding contraction, so that the cell-wall of the zygote generally lies in close contact with the conjugating cells. The conjugating cells in the others lie either transversely (e.g. Cosmarium, Fig. 37 d; Staurastrum, etc.), or parallel to one another (e.g. Penium, Closterium, etc.), and emit a short conjugation-canal (Fig. 37 d) from the centre of that side of each cell which is turned towards the other one. These canals touch, become spherical, and on the absorption of the dividing wall the aplanogametes coalesce in the swollen conjugation-canal (Fig. 37 e), which is often surrounded by a mucilaginous envelope. The zygote, which is often spherical, is surrounded by a thick cell-wall, consisting of three layers; the outermost of these[44] sometimes bears thorn-like projections, which in some species are simple (Fig. 37 f), in others branched or variously marked; in some, however, it remains always smooth (e.g. Tetmemorus, Desmidium). Deviation from this mode of conjugation may occur within certain genera (e.g. Closterium, Penium). Upon germination the contents of the zygote emerge, surrounded by the innermost layers of the wall (Fig. 37 g, h) and generally divide into two parts which develop into two new individuals, placed transversely to each other (Fig. 37 i); these may have a somewhat more simple marking than is generally possessed by the species.

Fig. 38.—Desmidiaceæ. A Closterium moniliferum; B Penium crassiusculum; C Micrasterias truncata (front and end view); D Euastrum elegans; E Staurastrum muticum (end view).

Order 2. Zygnemaceæ. Cell-wall without markings. The cells are cylindrical, not constricted in the centre, and (generally) united into simple, unbranched filaments. The whole contents of the conjugating cells take part in the formation of the zygote, which on germination grows out directly into a new filament.

Spirogyra is easily recognised by its spiral chlorophyll band; Zygnema has two star-like chromatophores in each cell (Fig. 40); both these genera are very common Algæ in ponds and ditches.

[45]

Fig. 39.—Spirogyra longata. A At the commencement of conjugation, the conjugation-canals begin to protrude at a and touch one another at b; the spiral chlorophyll band and cell-nuclei (k) are shown. B A more advanced stage of conjugation; a, a’ the rounded female and male aplanogametes: in b’ the male aplanogamete is going over to and uniting with the female aplanogamete (b).

Fig. 40.—A cell of Zygnema. S Pyrenoid.

Fig. 41.—Zygnema insigne, with zygote.

Fig. 42.—Germinating zygote of Spirogyra jugalis: the young plant is still unicellular; the end which is still in the wall of the zygote is elongated and root-like; the chromatophore divides and forms the spiral band.

The conjugation among the Zygnemaceæ takes place in the following manner: the cells of two filaments, lying side by side, or two cells, the one being situated above the other in the same filament (Fig. 41), push out small protuberances opposite each other (Fig. 39 A, a, b); these finally meet, and the dividing wall is absorbed so that a tube is formed connecting one cell with the other; the protoplasmic contents round off, and the whole of these contents of one of the cells glides through the conjugation-tube and coalesces with that of the other (Fig. 39 B), the aggregate mass then rounds off, surrounds itself with a cell-wall, and becomes a zygote. A distinct difference[46] may be found between the cells in the two filaments, those in the one whose protoplasmic contents pass over being cylindrical, while those of the recipient one are more barrel-shaped, and of a larger diameter. The former may be regarded as a male, the latter as a female plant. The zygote germinates after a period of rest, and grows out into a new filament (Fig. 42).

Order 3. Mesocarpaceæ. The cell-walls are glabrous, unconstricted in the centre, and united into simple unbranched filaments. The chromatophore consists of an axial chlorophyll-plate, with several pyrenoids. The zygote is formed by the coalescence of two cells (Fig. 43) (sometimes three or four), but the whole protoplasmic contents of the cells do not take part in this process, a portion always remaining behind; the aplanogametes coalesce in the conjugation-canal. The zygote thus formed appears incapable of germination until after 3–5 divisions. Of the cells so formed, only one is fertile, the sterile cells, according to Pringsheim, constituting a rudimentary sporocarp. The germinating cells grow out into a new filament. In this order, conjugation has been observed between two cells of the same filament. The Mesocarpaceæ thrive best in water which contains lime.

Fig. 43.—Mougeotia calcarea. Cells showing various modes of conjugation: at m tripartition; pg quadripartition; s quinquipartilion of the zygote.

Class 6. Chlorophyceæ (Green Algæ).

These Algæ are coloured green by chlorophyll, seldom in combination with other colouring matter, and then especially with red. The product of assimilation is frequently starch, which generally accumulates round certain specially formed portions of protoplasm termed pyrenoids. The thallus is uni- or multicellular; in the higher forms (certain Siphoneæ) the organs of vegetation attain differentiation into stem and leaf. The asexual reproduction takes place in various ways; the sexual reproduction is effected by conjugation of motile gametes, or by oogamous fertilisation. The[47] swarm-cells (zoospores, gametes, and spermatozoids) are constructed symetrically, and have true protoplasmic cilia, these generally being attached to the front end of the swarm-cells. Most of these Algæ live in water (fresh or salt); some are found upon damp soil, stones, or tree-stems, and some live enclosed in other plants.

The Class is divided into three families:—

1. Protococcoideæ: Volvocaceæ, Tetrasporaceæ, Chlorosphæraceæ, Pleurococcaceæ, Protococcaceæ, Hydrodictyaceæ.

2. Confervoideæ: Ulvaceæ, Ulothricaceæ, Chætophoraceæ, Mycoideaceæ, Cylindrocapsaceæ, Œdogoniaceæ, Coleochætaceæ, Cladophoraceæ, Gomontiaceæ, Sphæropleaceæ.

3. Siphoneæ: Botrydiaceæ, Bryopsidaceæ, Derbesiaceæ, Vaucheriaceæ, Phyllosiphonaceæ, Caulerpaceæ, Codiaceæ, Valoniaceæ, Dasycladaceæ.

Family 1. Protococcoideæ.

The Algæ which belong to this group are uni- or multicellular with the cells more or less firmly connected, sometimes in a definite, sometimes in an indefinite form (Fig. 47). Colonies are formed either by division or by small unicellular individuals becoming united in a definite manner; the colonies formed in this latter way are termed Cœnobia. Apical cells and branching are absent. Multiplication by division; asexual reproduction by zoospores, rarely by akinetes. Sexual reproduction may be wanting, or it takes place by isogamous, rarely by oogamous fertilisation.

Some are attached by means of a stalk to other objects (Characium, Fig. 49), others occur as “Endophytes” in the tissues of certain Mosses or Phanerogams, e.g. Chlorochytrium lemnæ, in Lemna trisulca; Endosphæra, in the leaves of Potamogeton, Mentha aquatica, and Peplis portula; Phyllobium, in the leaves of Lysimachia nummularia, Ajuga, Chlora, and species of Grasses; Scotinosphæra in the leaves of Hypnum and Lemna trisulca; the majority, however, live free in water and in damp places. Many species which were formerly considered to belong to this family have been proved to be higher Algæ in stages of development.

Order 1. Volvocaceæ. The individuals in this order are either uni- or multicellular, and during the essential part of their life are free-swimming organisms. They are generally encased in a mucilaginous envelope, through which 2–6 cilia project from every[48] cell. The vegetative reproduction takes place by the division of all, or a few, of the cells of the individual; in some a palmella-stage is found in addition. The sexual reproduction takes place by isogamous or oogamous fertilisation.

A. Unicellular Individuals. The principle genera are: Chlamydomonas, Sphærella, Phacotus.—Sphærella nivalis is the Alga which produces the phenomenon of “Red Snow,” well known on high mountains and on ice and snow fields in the polar regions. The red colouring matter which appears in this and other green Algæ, especially in the resting cells, is produced by the alteration of the chlorophyll.

Phacotus lenticularis has an outer covering incrusted with lime, which, at death, or after division, opens out into two halves. Species may be found among Chlamydomonas, in which conjugation takes place between gametes of similar size without cell-wall, but in C. pulvisculus conjugation takes place between male and female aplanogametes which are surrounded by a mucilaginous envelope.

Fig. 44.—Gonium pectorale.

Fig. 45.—Pandorina morum.

B. Multicellular Individuals. The most important genera are Gonium, Stephanosphæra, Pandorina, Eudorina, Volvox.—Gonium has 4 or 16 cells arranged in a definite pattern in a flat plate (Fig. 44). Pandorina (Fig. 45), has 16 cells arranged in a sphere (Fig. 45 A). The vegetative reproduction takes place in this way: each cell, after having rounded off, and after the withdrawal of the cilia, divides itself[49] into 16 new ones (Fig. 45 B), each forming a new individual, which soon grows to the size of the mother-individual. It was in this Alga that the conjugation of self-motile gametes was first discovered by Pringsheim, 1869. When conjugation is about to take place, each cell divides into sixteen, as in vegetative reproduction, but the 16 × 16 cells all separate from one another (Fig. 45 C, female gametes, and D, male gametes), and swarm solitarily in the water. The male are, most frequently, smaller than the female, but otherwise they are exactly alike; they are more or less pear-shaped, with a colourless anterior end, 2 cilia, a red “eye-spot,” etc. After swarming for some time they approach each other, two and two, generally a large and a smaller one, and come into contact at their colourless end; in a few moments they coalesce and become one cell (Fig. 45 E, F), this[50] has at first a large colourless anterior end, 4 cilia, and 2 “eye-spots” (Fig. 45 G), but these soon disappear and the cell becomes uniformly dark-green and spherical, and surrounds itself with a thick cell-wall, losing at the same time its power of motion: the zygote (Fig. 45 H) is formed, and becomes later on a deep red colour. On the germination of the zygote, the protoplasmic cell-contents burst open the wall (Fig. 45 J), and emerge as a large swarmspore (Fig. 45 K) which divides into 16 cells, and the first small individual is formed (Fig. 45 L, M).

Eudorina is like Pandorina in structure, but stands somewhat higher, since the contrast between the conjugating sexual cells is greater, the female one being a motionless oosphere.

Fig. 46.—Volvox globator, sexual individual: a antheridia which have formed spermatozoids; b oogonia.

The highest stage of development is found in Volvox (Fig. 46). The cells are here arranged on the circumference of a sphere, and enclose a cavity filled with mucilage. The number of these cells may vary from 200–22,000, of which the majority are vegetative and not reproductive, but some become large, motionless oospheres (Fig. 46 b); others, which may appear as solitary individuals, divide and form disc-shaped masses of from 8–256 small spermatozoids[51] (Fig. 46 a). After the oosphere has been fertilised by these, the oospore surrounds itself by a thick, sometimes thorny cell-wall, and on germination becomes a new individual of few cells. A few cells conspicuous by their larger size may be found (1–9, but generally 8) in certain individuals, and these provide the vegetative reproduction, each forming by division a new individual.

Order 4. Pleurococcaceæ. In this order the swarm-stages and sexual reproduction are entirely absent. Vegetative reproduction by division. The principal genera are: Pleurococcus (Fig. 47), Scenedesmus (Fig. 48), Raphidium, Oocystis, Schizochlamys, Crucigenia, Selenastrum.—Pleurococcus vulgaris (Fig. 47) is one of the most common Algæ throughout the world, occurring as green coverings on tree-stems, and damp walls, and it is one of the most common lichen-gonidia.

Fig. 47.—Pleurococcus vulgaris.

Fig. 48.—Scenedesmus quadricauda.

Order 5. Protococcaceæ. The cells are motionless, free or affixed on a stalk (e.g. Characium, Fig. 49), either separate or loosely bound to one another; they never form multicellular individuals. Multiplication by division is nearly always wanting. Reproduction takes place by swarmspores, which have 1 or 2 cilia, and sexual reproduction in some by gamete-conjugation. The principal genera are: Chlorococcum, Chlorochytrium, Chlorocystis, Scotinosphæra, Endosphæra, Phyllobium, Characium, Ophiocytium, Sciadium.

Fig. 49.—Characium strictum. A The cell-contents have divided into many swarmspores. B Swarmspores escaping.

Order 6. Hydrodictyaceæ. The individuals are unicellular but several unite after the zoospore-stage into definitely formed families (cœnobia). Ordinary vegetative division is wanting, but[52] asexual reproduction takes place by zoospores (or by motionless cells without cilia), which unite and form a family similar to the mother-family, inside the mother-cell, or in a mucilaginous envelope. Where sexual reproduction is found it takes place by gamete-conjugation. The principal genera are: Pediastrum (Fig. 50), Cœlastrum, Hydrodictyon (Fig. 51).

Fig. 5O.—Pediastrum asperum.

Fig. 51.—Hydrodictyou reticulatum. A A cell where the zoospores are on the point of arranging themselves to form a net. B A cell with gametes swarming out.

The cœnobium of Hydrodictyon reticulatum (Water-net) is formed of a large number of cells which are cylindrical, and attached to one another by the ends (Fig. 51). The asexual reproduction takes place by zoospores, which are formed in large numbers (7,000–20,000) in each mother-cell, within which they move about for a time, and then come to rest and arrange themselves into a new net (Fig. 51 A) which is set free by the dissolution of the wall of the mother-cell, grows, and becomes a new cœnobium. The sexual reproduction takes place by gamete-conjugation. The gametes are formed in the same manner as the zoospores, but in larger numbers (30,000–100,000), and swarm out of the mother-cell (Fig. 51 B). The zygote forms, on germination, 2–5 large zoospores, each with one or two cilia, these generally swarm about for a time, and after a period of rest become irregular thorny bodies (polyhedra); their contents again divide into zoospores, the thorny external coating of the polyhedra is cast off, and the zoospores, surrounded by the dilated internal coating, unite to form a small family, which produces several others in the manner described.

[53]

Family 2. Confervoideæ.

The individuals are always multicellular, the cells firmly bound together and united into unbranched or branched filaments, expansions, or masses of cells which grow by intercallary divisions or have apical growth. In the first seven orders the cells are uninuclear, but the cells of the remaining three orders contain several nuclei. Asexual reproduction by zoospores, akinetes or aplanospores. Sexual reproduction by isogamous or oogamous fertilisation.

Order 1. Ulvaceæ. The thallus consists of one or two layers of parenchymatous cells, connected together to form either a flat membrane (Monostroma, Ulva) or a hollow tube (Enteromorpha), and may be either simple, lobed, or branched. Reproduction takes place by detached portions of the thallus; or asexually by zoospores or akinetes. Gamete-conjugation is known to take place in some members of this order, the zygote germinating without any resting-stage. The majority are found in salt or brackish water.

Fig. 52.—Ulothrix zonata: a portion of a filament with zoospores, which are formed two in each cell (zoosporangium); the dark spots are the red “eye-spots”; 1, 2, 3, 4, denote successive stages in the development of the zoospores; b a single zoospore, v the pulsating vacuole; c portion of a filament with gametes, sixteen are produced in each gametangium; d free gametes, solitary or in the act of conjugation; e the conjugation is completed, and the formed zygote has assumed the resting-stage.

Order 2. Ulothricaceæ. The thallus consists normally of a simple unbranched filament (sometimes a small expansion consisting of one layer of cells is formed, as in Schizomeris and Prasiola which were formerly described as separate genera). Asexual reproduction takes place by means of zoospores (with[54] 1, 2, or 4 cilia), akinetes or aplanospores; the last named may germinate immediately, or only after a period of rest. Sexual reproduction takes place by the conjugation of gametes of about the same size, each having two cilia (Fig. 52 d). The zygote of Ulothrix, on germination, produces a brood of zoospores which swarm for a time and then elongate to become Ulothrix-filaments (alternation of generations). The gametes may also germinate without conjugation in the same manner as the zoospores. The principal genera are: Ulothrix, Hormidium, Conferva, Microspora.—Ulothrix zonata is very common in running fresh water. Nearly all the species of Hormidium occur on damp soil, tree-stems and stones.

Order 3. Chætophoraceæ. The thallus consists of a single, branched, erect or creeping filament of cells, often surrounded by mucilage. The cells have only one nucleus. Asexual reproduction by zoospores with 2 or 4 cilia, by akinetes, or aplanospores. In many, conjugation between gametes with 2 cilia may be found. They approach on one side, Ulothricaceæ, and on the other, Mycoideaceæ. The principal genera are: Stigeoclonium, Draparnaldia, Chætophora, Entoderma, Aphanochæte, Herposteiron, Phæothamnion, Chlorotylium, Trichophilus, Gongrosira, Trentepohlia. Most of the species of Trentepohlia are coloured red by the presence of a red colouring material, which occurs in addition to the chlorophyll. They are aerial Algæ which live on stones (T. jolithus, “violet stone,” so named on account of its violet-like odour in rainy weather), on bark and old wood (T. umbrina), or on damp rocks (T. aurea). Trichophilus welckeri lives in the hair of Bradypus.

Order 5. Cylindrocapsaceæ. The thallus consists of a simple (rarely, in parts, formed of many rows) unbranched filament, attached in the young condition, which has short cells with a single nucleus, and is enveloped in a thick envelope with a laminated structure. Asexual reproduction by zoospores with 2 cilia, which are formed 1, 2, or 4 in each vegetative cell. The[55] antheridia are produced by a single cell, or a group of cells, in a filament, dividing several times without increasing in size. Two egg-shaped spermatozoids, each with 2 cilia (Fig. 53 D), are formed in each antheridium, and escape through an aperture in the side; in the first stages they are enclosed in a bladder-like membrane (Fig. 53 B, C). Other cells of the filament swell out and form oogonia (Fig. 53 A), which resemble those of Œdogonium. After fertilisation, the oospore surrounds itself with a thick wall, and assumes a reddish colour. The germination is unknown. The unfertilised oospheres remain green, divide often into 2–4 daughter-cells, and grow into new filaments.

Fig. 53.—Cylindrocopsa involuta. A Oogonium with oosphere (o) surrounded by spermatozoids (s). B Two antheridia, each with two spermatozoids. C Spermatozoids surrounded by their bladder-like membrane. D Free spermatozoid.

This order, which only includes one genus, Cylindrocapsa, forms the connecting link between Ulothricaceæ and Œdogoniaceæ. The few species (4) occur only in fresh water.

Order 6. Œdogoniaceæ. The thallus consists of branched (Bulbochæte) or unbranched (Œdogonium) filaments, attached in the early stages. The cells may be longer or shorter, and have one nucleus. Asexual reproduction by zoospores, which have a chaplet of cilia round the base of the colourless end (Fig. 6 a). Sexual reproduction takes place by oogamous fertilisation. On the germination of the oospore, 4 zoospores are formed (Fig. 54 F). They occur only in fresh or slightly brackish water. The division[56] of the cells takes place in quite a peculiar and unusual manner. At the upper end of the cell which is about to divide, a ring-shaped thickening of soft cellulose is formed transversely round the wall; the cell-nucleus of the mother-cell and the protoplasm then divide by a transverse wall into two portions of similar size, and the cell-wall bursts transversely along the central line of the thickened ring. The cell-wall thus divides into two parts—the upper one short, the “cap,” and the lower one much longer, the “sheath.” The portions of the original cell-wall now separate from each other, the cellulose ring extending, and supplying an additional length of cell-wall between them. The cap and sheath will project a little in front of the piece thus inserted. The dividing wall between the two new cells is formed near to the uppermost edge of the sheath, and gradually becomes thicker and firmer. The inserted piece of wall forms the larger part of the wall of the upper cell: the remainder is formed by the cap. This mode of division is repeated exactly in the same way, and new caps are formed close below the first one, one for every division.

Fig. 54.—A Œdogonium ciliatum. A Female plant with three oogonia (og) and dwarf-males (m). B An oogonium with spermatozoid (z) seen entering the oosphere (o) having passed through an aperture near the summit of the oogonium; m dwarf-male. C Ripe oospore. D Œdogonium gemelliparum. F Portion of a male filament from which spermatozoids (z) are emerging. E Portion of filament of Bulbochæte; the upper oogonium still encloses the oospore, in the central one the oospore is escaping while the lower one is empty. F Four zoospores developed from an oospore. G Zoospore germinating.

[57]

Fertilisation takes place in the following way. The oogonium is a large ellipsoidal, swollen cell (og, in Fig. 54 A), whose contents are rounded off into an oosphere with a colourless receptive-spot (see B); an aperture is formed in the wall of the oogonium, through which the spermatozoids are enabled to enter (B). The spermatozoids are produced either directly, as in D (in pairs), in basal cells of the filament, or indirectly. In the latter case a swarmspore (androspore) is formed which comes to rest, attaches itself to an oogonium, germinates, and gives rise to a filament of a very few cells—dwarf-male (A, B, m). The spermatozoids are formed in the upper cell of the dwarf-male (m), and are set free by the summit of the antheridium lifting off like a lid. On the germination of the oospore (C), which takes place in the following spring, 4 zoospores are produced (F) (i.e. the sexual generation); these swarm about for a time, and ultimately grow into new filaments.

Fig. 55.—Coleochæte pulvinata. A A portion of a thallus with organs of reproduction; a oogonium before, b after fertilisation; c an antheridium, closed; d open, with emerging spermatozoid. B Ripe oogonium, with envelope. C Germination of the oospore. D Zoospore. E Spermatozoid.

Order 7. Coleochætaceæ. The thallus is always attached, and of a disc- or cushion-shape, formed by the dichotomous branching of filaments of cells united in a pseudo-parenchymatous manner. Each cell has only one nucleus. Asexual reproduction by zoospores with 2 cilia (Fig. 55 D), which may arise in all the cells. Sexual reproduction by oogamous fertilisation. The spermatozoids resemble the swarmspores, but are[58] smaller (E), and originate singly (in the species figured) in small conical cells (c, d in A). The oogonia are developed at the extremities of certain branches: they are bottle-shaped cells with very long and thin necks (trichogyne), open at the end (a in A); at the base of each oogonium is a spherical oosphere. The spermatozoids reach the oosphere through the trichogyne, or through an aperture in the wall when the trichogyne is absent, and fertilisation having taken place, the oogonium becomes surrounded by a cell-layer (envelope), which grows out from the cells near its base (b in A), and in this way a kind of fruit is formed (B) (spermocarp, cystocarp).

The oospore, next spring, divides and forms a parenchymatous tissue (homologous with the Moss-sporophyte); this bursts open the envelope (C), and a zoospore (homologous with the spores of the Moss-capsule) arises in each of the cells, and produces a new Coleochæte. We have then, in this case, a still more distinct alternation of generations than in Œdogonium. Only one genus, Coleochæte, is known, but it contains several species, all living in fresh water.

Order 8. Cladophoraceæ. This order is probably derived from the Ulothricaceæ. The thallus consists of a single, unbranched or branched filament, generally with an apical cell. The cells have each 2 or more nuclei. Asexual reproduction by zoospores with 2 or 4 cilia, and by akinetes. Conjugation of gametes with 2 cilia is found in some genera. They occur in salt as well as in fresh water. The principal genera are: Urospora, Chætomorpha, Rhizoclonium, Cladophora; of the last named genus the species C. lanosa and C. rupestris are common in salt water; C. fracta and C. glomerata in fresh water.

Order 10. Sphæropleaceæ. The thallus consists of free, unbranched filaments, with very elongated multinuclear cells. The vegetative cells form no zoospores. Sexual reproduction by oogamous fertilisation (see page 13, Fig. 10 B). The oospore has a thick wall (Fig. 10 D) studded with warts, and assumes a colour resembling red lead. It germinates only in the following spring, and produces 1–8 zoospores, each with 2 cilia (Fig. 10 E), which grow into new filaments. Only one species, Sphæroplea annulina, is known.

[59]

Family 3. Siphoneæ.

The thallus has apical growth, and in the vegetative condition consists generally of one single (in the Valoniaceæ most frequently of more) multinuclear cell, which may be much branched, and whose separate parts in the higher forms (e.g. Bryopsis, Fig. 57; Caulerpa, Fig. 59, etc.) may be differentiated to perform the various physiological functions (as root, stem and leaf). Vegetative multiplication by detached portions of the thallus (gemmæ); asexual reproduction by zoospores, akinetes, or aplanospores. Sexual reproduction by gamete-conjugation, rarely by oogamous fertilisation. The zygote or oospore germinates as a rule without any resting-stage.

Fig. 56.—Botrydium granulatum: a an entire plant forming swarmspores; b swamspores; c an individual with gametangia; d, gamete; e, f, g conjugation; h zygote seen from above; i the same in a lateral view.

Most of the Siphoneæ occur in salt water or on damp soil. Many (e.g. Dasycladaceæ) are very much incrusted with lime, and occur, in the fossilized condition, in the deposits from the Cretaceous period to the present time. The Siphoneæ are connected by their lowest forms (Botrydiaceæ or Valonia) with the Protococcaceæ, but show also, through the Valoniaceæ, points of relationship to the Cladophoraceæ.

Order 1. Botrydiaceæ. The thallus in the vegetative condition is unicellular, club-shaped, with a small single (Codiolum) or repeatedly dichotomously branched system of colourless rhizoids (Botrydium, Fig. 56 a), by which it is attached to objects immersed in salt water (Codiolum) or to damp clay soil (Botrydium). Asexual reproduction by zoospores with one (Botrydium) or two[60] cilia, and by aplanospores. The sexual reproduction is only known in Botrydium, and takes place in the following manner: in the part of the thallus which is above ground and in an active vegetative condition, several round cells (Fig. 56 c) are formed, which may be green or red according as they grow under water, or exposed to the strong light of the sun. These cells must be considered as “gametangia” as they produce many gametes (d) provided with two cilia. The zygote (h, i) formed by the conjugation (e, f, g) may either germinate immediately, or become a thick-walled resting-cell of an irregular, angular form.

Fig. 57.—Bryopsis plumosa. A the plant, natural size. B A portion (enlarged) which shows the growing point (v), and the leaves derived from it in acropetal succession.

Order 4. Vaucheriaceæ. The thallus consists, in the vegetative condition, of a single irregularly or dichotomously branched cell, without differentiation into stem or leaf; root-like organs of attachment may however occur. Asexual reproduction by zoospores, which are formed singly in the extremity of a branch cut off by a transverse wall. They contain many nuclei, and bear small cilia situated in pairs, which give the appearance of a fine “pile” covering the whole or a great part of the surface. Akinetes,[61] aplanospores, and phytoamœbæ (naked masses of protoplasm, without cilia, which creep like an amœba on a substratum) may occur under certain conditions.

The sexual reproductive organs are formed on short lateral branches, and are separated from the vegetative cell (Fig. 58 A) by cell-walls. Numerous spermatozoids, each with two cilia, are developed in the coiled antheridium (A, b). The oogonium is a thick, egg-shaped, often oblique cell, with its protoplasm rounded into an oosphere, which has a hyaline “receptive-spot” (A, a) immediately beneath the aperture formed in the wall of the oogonium. A slimy mass, which serves to receive the spermatozoids, is formed in some species in this aperture. The spermatozoids when liberated swim towards and enter the oosphere, which then immediately surrounds itself with a thick cell-wall. The mature oospore (B) contains a large quantity of oil. At germination the outer cell-wall bursts and a new plant is formed. There is only one genus, Vaucheria, with species living in salt as well as in fresh water and on damp soil.

Fig. 58.—Vaucheria sessilis. A Fertilisation; b the antheridia; a the oogonia; a the receptive spot. B Oospore.

Order 6. Caulerpaceæ. The thallus has distinct differentiation into root, stem and leaf-like members (Fig. 59); it is unicellular. Within the cell, strong, branched threads of cellulose extend from one side to the other serving as stays to support the thallus. Reproduction takes place by detached portions of the thallus; no other modes of reproduction are known. This order may most approximately be classed with the Bryopsidaceæ. The genus Caulerpa consists of more than seventy species which inhabit the tropical seas.

Order 7. Codiaceæ. The thallus has various forms, but without[62] distinct differentiation in stem- or leaf-structures, sometimes (e.g. Halimeda) it is very much incrusted with lime. In the early stages it is unicellular (later, often multicellular), very much branched, with the branches, at any rate partly, so united or grown in amongst one another (Fig. 60) that an apparently parenchymatous cellular body is formed. Akinetes or aplanospores are wanting; zoospores (or gametes?) may be developed in some species, however, in special swollen sporangia. Fertilisation similar to that in Bryopsis occurs perhaps in Codium. They are all salt water forms.

Fig. 59.—Caulerpa prolifera (natural size).

[63]

Order 9. Dasycladaceæ. The thallus consists of an axile longitudinal cell, destitute of transverse walls, attached at the base by root-like organs of attachment, and producing acropetally whorls of united, single or branched, leaf-like structures with limited growth. Asexual reproduction is wanting. Sexual reproduction by conjugation of gametes which arise in separate, fertile leaves, either directly or from aplanospores, which develope into gametangia. The principal genera are: Acetabularia, Dasycladus, Neomeris, Cymopolia. All marine.

Fig. 60.—Halimeda opuntia. Plant (natural size). B Part of a longitudinal section.

The curiously shaped Acetabularia mediterranea grows gregariously on limestone rocks, and shells of mussels in the Mediterranean; it resembles a minute umbrella with a small stem, sometimes as much as nine centimetres in height, and a shade which may be more than one centimetre in diameter. The cell-membrane is thick, and incrusted with carbonate and oxalate of lime. Only the lower, root-like part of the thallus, which penetrates the calcareous substratum survives the winter, and may grow up into a new plant. The sterile leaves, which drop off early, are dichotomously branched and formed of cylindrical cells separated from each other by cross-walls, but they are not grown together. The shade is formed by a circle of 70–100 club-shaped rays (fertile leaves) grown together, in each ray 40–80 aplanospores are formed, which become liberated at the breaking of the shade, and later on are changed to gametangia (compare Botrydium) which open by a lid and allow a large number of egg-shaped gametes with two cilia to escape. Gametes from various[64] gametangia conjugate with one another; the product of the conjugation swarms about for some time, rounds off, and then surrounds itself with a cell-wall. The zygote germinates after a period of rest and then produces a sexual plant. The aplanospores (gametangia) thus represent the sexual generation.

Class 7. Characeæ.

The thallus has a stem with nodes and internodes; and whorls of leaves, on which may be developed the antheridia and oogonia, are borne at the nodes. Vegetative reproduction by bulbils and accessory shoots. Zoospores are wanting. The antheridia are spherical, and contain a number of filaments in which the spirally coiled spermatozoids, each with two cilia, are formed. The oogonium is situated terminally, and is at first naked, but becomes later on surrounded by an investment, and forms after fertilisation the so-called “fruit.” The oospore, after a period of rest, germinates by producing a “proembryo,” from which the young sexual plant arises as a lateral branch. The Characeæ are distinguished by the structure of their vegetative system as well as by the spirally-coiled spermatozoids, and stand as an isolated group among the Thallophytes, of which, however, the Siphoneæ appear to be their nearest relations. They were formerly, but wrongly, placed near the Mosses. The class contains only one order, the Characeæ.

Order 1. Characeæ. Algæ with a peculiar odour, often incrusted with lime, and of a brittle nature. They generally grow gregariously in large masses at the bottom of fresh and brackish water, and are from a few inches to more than a foot in height. The stem has long internodes which in Nitella are formed of one cylindrical cell; in Chara of a similar cell, but closely surrounded by a cortical layer of smaller ones. The protoplasm in contact with the cell-wall exhibits in a well-marked degree the movement of rotation (cyclosis), carrying the chlorophyll corpuscles along with it. The internodes are separated from each other by a layer of small cells (nodal cells) from which the leaves are produced. The leaves are borne in whorls of from 5–12 which regularly alternate with one another as in the higher verticillate plants; a branch is borne in the axil of the first formed leaf of each whorl (Fig. 61 A, n).

Fig. 61.—Chara fragilis. A Portion of a plant, natural size. B Portion of a leaf b, with leaflets β′-β′′; a antheridium; c oogonium. C A shield.—Nitella flexilis. D Filament from antheridium with spermatozoids. E Free spermatozoids.

The leaves are constructed in the same manner as the stem; they are divided into a series of joints, but have only a limited[65] power of growth; their terminal cell, too, is not enclosed by a cortex. Leaflets are borne at their nodes. The growth of the stem is unlimited, and proceeds by means of an apical cell (Fig. 62 s). The apical cell divides into a segment-cell and a new apical cell. The segment-cell then divides by a transverse wall into two cells, one lying above the other; the lower one, without any further division, becomes one of the long, cylindrical, internodal cells (Fig. 62 in), and the upper one (Fig. 62 n) divides by vertical walls to form the nodal cells. The cortical cells (Fig. 62 r) which surround the long internodal cells of Chara, are derived from the divisions of the nodal cells; the cells covering the upper portion of an internodal cell being derived from the[66] node immediately above it, and those in the lower part of the internode from the node below it.

Fig. 62.—Chara fragilis: s apical cell; n, n nodal cells; in internodal cells; bl, bl leaves; r, r the cortical cells.

Fig. 63.—Oogonium of Chara: k “crown”; u receptive spot; s spermatozoids.

The organs of reproduction are very conspicuous by their colour and form. They are always situated on the leaves, the plants being very frequently monœcious. The antheridia (Fig. 61 B, a) are modified leaflets or the terminal cell of a leaf; they are spherical and become red when mature. Their wall consists of 8 “shields,” i.e. of plate-like cells, 4 of which cover the upper half, and are triangular; the 4 round the lower half, to which the stalk of the antheridia is attached, being quadrilateral, with sides of unequal length. The shields (Fig. 61 C) have dentated edges, with the teeth fitting into one another, and their faces ornamented with ridges. From the centre of the internal face of each shield (C) a cylindrical cell, the manubrium, projects nearly as far as the centre of the antheridium; at the inner end of each of the manubria a spherical cell, the capitulum, is situated. Each capitulum bears six secondary capitula, from each of which four long coiled filaments (C, D) project into the cavity of the antheridium. These filaments are divided by transverse walls into from 100–200 discoid cells, in each of which a biciliated, coiled spermatozoid is developed (D, E) from the nucleus. The spermatozoids escape from their mother-cell and are set free by the shields separating from one other.

[67]

The female organ of reproduction (Fig. 61 B, 63) is a small modified shoot, whose apical cell functions as an oogonium, its protoplasm forming the oosphere, which has a colourless receptive-spot at the summit (Fig. 63 u). The oogonium is situated on a nodal cell, from which 5 cells grow out in a circle and coil round the oogonium, covering it with a close investment. These cells divide once or twice at the top, so that 5 or 10 small cells are cut off, which project above the oogonium and form the so-called “crown” (Fig. 63 k). The crown either drops off at fertilisation, or its cells separate to form a central canal for the passage of the spermatozoids. The wall of the oosphere[9] above the receptive spot becomes mucilaginous, and allows the spermatozoid to fuse with the oosphere. The oospore, on germination (Fig. 64 sp), becomes a small filamentous plant of limited growth (Fig. 64 i, d, q, pl)—the proembryo—and from this, as a lateral outgrowth, the sexual generation is produced.

The order is divided into two sub-orders:—

A. Nitelleæ. The crown consists of 10 cells; cortex absent: Nitella, Tolypella.

B. Chareæ. The crown consists of 5 cells; cortex present: Tolypellopsis, Lamprothamnus, Lychnothamnus, Chara.

Chara crinita is parthenogenetic; in large districts of Europe only female plants are found, yet oospheres are formed capable of germination.

Fig. 64.—Chara fragilis. Germinating oospore (sp); i, d, g, pl, form together the proembryo rhizoids (w′) are formed at d; w′ the so-called tap-root; at g are the first leaves of the sexual plant, which appears as a lateral bud.

About 40 species of fossilized Chara, determined by their carpogonia, are known in the geological formations from the Trias up to the present day.

[68]

Class 8. Phæophyceæ (Olive-Brown Seaweeds).

The Phæophyceæ are Algæ, with chromatophores in which the chlorophyll is masked by a brown colour (phycophæin). The product of assimilation is a carbohydrate (fucosan), never true starch. In the highest forms (Fucaceæ), the thallus presents differentiation into stem, leaf, and root-like structures. The asexual reproduction takes place by means of zoospores. The sexual reproduction is effected by the coalescence of motile gametes, or by oogamous fertilisation. The swarm-cells are monosymmetric, each moved by two cilia which are true protoplasmic structures, and generally attached laterally (Fig. 65). The Phæophyceæ are almost entirely saltwater forms; a few species of Lithoderma live in fresh water.

The class is divided into two families:—

1. Phæosporeæ: 1 Sub-Family, Zoogonicæ; 2 Sub-Family, Acinetæ.

2. Cyclosporeæ: Fucaceæ.

Family 1. Phæosporeæ.

The family consists of multicellular plants, whose cells are firmly united together to form a thallus; this, in the simplest cases, may be a branched filament of cells (Ectocarpus), or, in the highest, may resemble a stem with leaves (Laminariaceæ), while all transitional forms may be found between these two. The thallus grows by intercalary divisions (e.g. Ectocarpus), or by an apical cell (e.g. Sphacelaria); pseudo-parenchymatous tissue may sometimes be formed by cells, which were originally distinct, becoming united together. The size of the thallus varies; in some species it is quite small—almost microscopical,—while in the largest it is many metres in length.

The vegetative cells in the lower forms are nearly uniform, but in those which are more highly developed (Laminariaceæ and Fucaceæ), they are sometimes so highly differentiated that mechanical, assimilating, storing and conducting systems may be found; the last named systems are formed of long cells with perforated, transverse walls, which bear a strong resemblance to the sieve-tubes in the higher plants.

Fig. 65.—Swarmspore of Cutleria multifida.

The colouring matter in the living cells (“phæophyl”) contains[69] chlorophyll; but this is concealed by a brown (“phycophæin”), and a yellow (“phycoxanthin”) colouring material, and hence all these Algæ are a lighter or darker yellow-brown. Starch is not formed. Asexual reproduction takes place, (1) by zoospores which arise in unilocular zoosporangia, and are monosymmetric, with two cilia attached laterally at the base of the colourless anterior end (Fig. 65), the longer one being directed forwards and the shorter backwards; or (2) by aplanospores (?).

Fig. 66.—Ectocarpus siliculosus. I a-f A female gamete in the various stages of coming to rest. II A motionless female gamete surrounded by male gametes. III a-e Stages in the coalescence of male and female gametes.

Fig. 67.—Zanardinia collaris. A Male gametangia (the smaller celled) and female gametangia (the larger celled). C Female gamete. D Male gamete. B, E Fertilisation. F Zygote. G Germinating zygote.

Sexual reproduction has only been discovered in a few cases, and takes place by means of gametes (oogamous fertilisation perhaps occurs in the Tilopteridæ). The gametes have the same structure as the zoospores, and arise in multilocular gametangia; these, like the zoosporangia, are outgrowths from the external surface, or arise as modifications from it. The conjugating gametes may be similar (e.g. Ectocarpus pusillus), or there may be a more or less pronounced difference of sex, an indication of which is found in Ectocarpus siliculosus (Fig. 66). When the gametes in this species have swarmed for a time, some, which are generally larger,[70] are seen to attach themselves by one of the cilia, which by degrees is shortened to form a kind of stalk (compare the upper gamete in Fig. 66 II); these are the female gametes, which now become surrounded by a number of males endeavouring to conjugate with them, but only one succeeds in effecting fertilisation. The protoplasm of the two gametes coalesces (Fig. 66 III), and a zygote (e) is formed. The male gametes which do not conjugate may germinate, but the plants derived from them are much weaker than those produced by the zygotes. Strongly pronounced sexual differences are found in the Cutleriaceæ, in which order the male and female gametes arise in separate gametangia (Fig. 67 A). The male gametes (Fig. 67 D) are much smaller than the female gamete (Fig. 67 C); the latter, after swarming for a short time, withdraws the cilia, and is then ready to become fertilised (Fig. 67 B, E), thus we have here a distinct transition to the oogamous fertilisation which is found in the Fucaceæ. Alternation of generations is rarely found.

1. Sub-Family. Zoogonicæ.

Reproduction by means of gametes and zoospores.

Order 1. Ectocarpaceæ. The thallus consists of single or branched filaments with intercalary growth, extending vertically from a horizontal, branched filament or a disc, but sometimes it is reduced to this basal portion only. Zoosporangia and gametangia (for fertilisation see Fig. 66) are either outgrowths or arise by the transformation of one or several of the ordinary cells. The most common genera are: Ectocarpus and Pylaiella.

Order 2. Choristocarpaceæ. Choristocarpus, Discosporangium.

Order 3. Sphacelariaceæ. The thallus consists of small, parenchymatous, more or less ramified shoots, presenting a feather-like appearance. In the shoots, which grow by means of an apical cell (Fig. 68 S), a cortical layer, surrounding a row of central cells, is present. Sporangia and gametangia are outgrowths from the main stem or its branches. Sphacelaria, Chætopteris are common forms.

Fig. 68.—Apex of the thallus of Chætopteris plumosa. S Apical cell.

Fig. 69.—Laminaria digitata (much reduced in size).

Order 16. Laminariaceæ. The thallus is more or less leathery, and has generally a root-like lower part (Fig. 69) which serves to attach it, and a stalk or stem-like part, terminated by a large leaf-like expansion. Meristematic cells are situated at the base of the leaf, and from these the new leaves are derived. The older leaf thus pushed away by the intercalary formation of the younger ones, soon withers (Fig. 69). Gametes are wanting. Zoosporangia are developed from the lower part of a simple, few-celled sporangiophore, which is an outgrowth from a surface-cell and has a large club-formed apical cell. The sporangia are aggregated into closely packed sori, which cover the lower part of the terminal leaf, or occur on special, smaller, lateral, fertile fronds (Alaria). Most of the species belonging to this order live in seas of moderate or cold temperature and occur in the most northern regions that have yet been explored, forming their organs of reproduction during the cold and darkness of the arctic night. Laminaria is destitute of a midrib and has only one terminal leaf.[72] L. digitata has a broad leaf, which, by the violence of the waves, is torn into a number of palmate strips (Fig. 69). L. saccharina has a small, undivided leaf. Alaria has a midrib and special fertile fronds. A. esculenta occurs plentifully on the west coast of Norway and on the shores of Great Britain. Chorda filum, a common seaweed, is thick, unbranched, and attains a length of several metres, without any strong demarcation between stalk and leaf. Some attain quite a gigantic size, e.g. Macrocystis pyrifera, whose thallus is said sometimes to be more than 300 metres in length. The Lessonia-species, like the above, form submarine forests of seaweed on the south and south-west coasts of South America, the Cape, and other localities in the Southern Hemisphere.

Order 17. Cutleriaceæ. The thallus is formed by the union of the originally free, band-shaped shoots. The growth is intercalary. Sexual reproduction by the conjugation of male and female gametes. An asexual generation of different appearance, which produces zoospores, arises from the germination of the zygote. Cutleria, Zanardinia.

Sub-Family 2. Acinetæ.

Branched, simple cell-rows with intercalary growth. The organs of reproduction are partly uni-and partly multicellular; in the unicellular ones a cell without cilia is formed, which may be destitute of a cell-wall, but has one nucleus (oosphere?), or which has a cell-wall and contains several (generally four) nuclei (aplanospores?); in the multicellular, monosymmetric swarm-cells with two cilia (spermatozoids?) are formed. The fertilisation has not been observed.

Order 1. Tilopteridaceæ. Haplospora, Tilopteris.

[73]

Family 2. Cyclosporeæ.

The individuals are multicellular, with growth by an apical cell. The thallus—often bilateral—is differentiated into a root-like structure (attachment-disc), and stem, sometimes also into leaves (Sargassum). Sometimes a differentiation occurs into various tissue-systems, viz. an external assimilating tissue, a storing tissue, a mechanical tissue of thickened, longitudinal, parenchymatous, strengthening cells, and a conducting tissue of sieve-cells, or of short sieve-tubes with perforated walls. Colouring material, as in Phæosporeæ. Vegetative reproduction can only take place by means of detached portions of the thallus (Sargassum), which are kept floating by means of bladders (Fig. 70 A, a, Fig. 72). Zoospores are wanting.

The sexual reproduction takes place by oogamous fertilisation. The oogonia and antheridia are formed inside special organs (conceptacles), and are surrounded by paraphyses. The conceptacles (Fig. 70 B, Fig. 71 b) are small, pear-shaped or spherical depressions, produced by a special ingrowth of the surface cells of the thallus, and their mouths (ostioles) project like small warts; they are either situated near the end of the ordinary branches of the thallus (Fucus serratus, Fig. 71 a) which may be swollen on this account (Fucus vesiculosus, Fig. 70 A, b), or on special short branches (Ascophyllum, Sargassum). The vertical section of a conceptacle is seen in Fig. 70 B (see also Fig. 71 b) where, in addition to the paraphyses, oogonia only are seen (F. vesiculosus is diœcious—male plant, yellow-brown; female plant, olive-brown); but in some species antheridia, together with oogonia, are produced in the same conceptacle. The oogonia are large, almost spherical cells, situated on a short stalk, in each of which are formed from 1–8 (in Fucus, 8; in Ascophyllum, 4; in Halidrys, 1; in Pelvetia, 2) rounded, immotile oospheres. The wall of the oogonium ruptures, and the oospheres, still enclosed in the inner membrane, are ejected through the mouth of the conceptacle, and float about in the water, being finally set free by the bursting of the inner membrane. The antheridia are oblong cells (Fig. 70 C, a), many of which are produced on the same branched antheridiophore (Fig. 70 C); the numerous spermatozoids are provided with 2 cilia and are very small (Fig. 70 D, two antheridia surrounded by spermatozoids, one being open). The spermatozoids, still enclosed by the inner membrane of the antheridium, are[74] similarly set free, and fertilisation takes place in the water, numerous spermatozoids collecting round the oosphere (Fig. 70 E), which is many times larger, and by their own motion causing it to rotate. After fertilisation, the oospore surrounds itself with a cell-wall and germinates immediately, attaching itself (Fig. 70 F) to some object, and by cell-division grows into a new plant.

Fig. 70.—Fucus vesiculosus. A Portion of thallus with swimming bladders (a) and conceptacles (b). B Section of a female conceptacle; h the mouth; p the inner cavity; s oogonia. C Antheridiophore; a antheridium; p sterile cells. D Antheridia out of which the spermatozoids are escaping. E Fertilisation. F Germinating oospore.

[75]

Fig. 71.—Fucus serratus. a Portion of a male plant which has been exposed to the action of the open air for some time; small orange-yellow masses, formed by the antheridia, are seen outside the mouths of the male conceptacles (nat. size). b Cross section through the end of a branch of a female plant, showing the female conceptacles (× 4).

Fig. 72.—Sargassum bacciferum. A portion of the thallus, natural size.

Order 1. Fucaceæ. The following species are common on our coasts: Fucus vesiculosus (Fig. 70) has a thallus with an entire margin, and with bladders arranged in pairs; F. serratus (Fig. 71) without bladders, but with serrated margin; Ascophyllum nodosum has strap-like shoots, which here and there are swollen to form bladders; Halidrys siliquosa has its swimming bladders divided by transverse walls; Himanthalia lorea, which is found on the west coast of Norway, and the south coast of England, has a small perennial, button-shaped part, from the centre of which proceeds the long and sparsely branched, strap-like, annual shoot, which bears the conceptacles. The Gulf-weed (Sargassum bacciferum, Fig. 72) is well known historically from the voyage of Columbus; it is met with in large, floating, detached masses in all oceans, and is found most abundantly in the Atlantic, off the Canary Islands and the Azores, and towards the Bermudas. The stalked, spherical air-bladders are the characteristic feature of this genus. The thallus is more highly developed than in Fucus, and there is a contrast between the stem and leaf-like parts. The[76] portions which are found floating are always barren, only those attached are fertile.

Class 9. Dictyotales.

The plants in this class are multicellular, and brown, with apical growth, new cells being derived either from a flat apical cell, or from a border of apical cells. The thallus is flat, leaf- or strap-shaped, attached by haptera, which are either found only at the base, or on the whole of the lower expansion of the thallus. The cells are differentiated into the following systems of tissues: an external, small-celled layer of assimilating cells, generally one cell in thickness, and an internal, large-celled layer of one or only a few cells in thickness, forming the mechanical and conducting tissues. All the reproductive cells are motionless. Asexual reproduction by naked, motionless spores (tetraspores) which are formed 1–4 in each tetrasporangium, the latter being outgrowths from the surface cells of special, sexless individuals. Zoospores are wanting. The sexual organs are of two kinds, oogonia and antheridia, which are formed from the surface cells, either on the same or different individuals. The oogonia are spherical or oval, and are generally placed close together; each contains one oosphere, which on maturity is ejected into the surrounding water, and is then naked and motionless. The antheridia are formed of longitudinal cells, united in groups, whose contents by repeated divisions—transverse and longitudinal—are divided into a large number of small, colourless, motionless spermatia—round or elongated—which are set free by the dissolution of the wall of the antheridium. The process of fertilisation has not yet been observed.

The Dictyotales, in having tetraspores and spermatia, deviate considerably from the Phæophyceæ, but may be classed near to the Tilopteridæ, in which there are asexual spores with 4 cell-nuclei, which may be considered as an indication of the formation of tetraspores.

[77]

Class 10. Rhodophyceæ (Red Seaweeds).

The plants comprised in this class are multicellular; they are simple or branched filaments, or expansions consisting of 1 to several layers of cells; the thallus may be differentiated (as in many Florideæ), to resemble stem, root, and leaf. The cells contain a distinctly differentiated nucleus (sometimes several), and distinct chromatophores, coloured by rhodophyll. The chlorophyll of the chromatophores is generally masked by a red colouring matter (phycoerythrin), which may be extracted in cold, fresh water; or rarely by phycocyan. Pyrenoids occur in some. Starch is never formed in the chromatophores themselves, but a modification—Florideæ starch—may be found in the colourless protoplasm. Asexual reproduction by motile or motionless spores (tetraspores) which are devoid of cilia and of cell-wall. Swarmspores are never found.

Sexual reproduction is wanting, or takes place by the coalescence of a spermatium and a more or less developed female cell. The spermatia are naked masses of protoplasm, devoid of cilia and chromatophores. The female cell (carpogonium) is enclosed by a cell-wall, and after fertilisation forms a number of spores, either with or without cell-walls (carpospores), which grow into new individuals.

The Rhodophyceæ may be divided into two families:

1. Bangioideæ.

2. Florideæ.

Family 1. Bangioideæ.

The thallus consists of a branched or unbranched cell-filament, formed of a single row or of many rows of cells, or of an expansion, one or two layers of cells in thickness, but without conspicuous pores for the intercommunication of the cells. The growth of the thallus is chiefly intercalary. The star-like chromatophores contain chlorophyll and are coloured blue-green with phycocyan, or reddish with phycoerythrin; all these colouring matters are occasionally found in the same cell (Bangia-species). Asexual reproduction by tetraspores, without cilia, but capable of amœboid movements.

Sexual reproduction is wanting, or takes place by the coalescence of a spermatium with a carpogonium, which is only slightly differentiated from the vegetative cells, and is devoid of a trichogyne.[78] The carpospores are destitute of cell-wall and arise directly by the division of the fertilised oosphere. The Bangioideæ occur chiefly in salt water.

Family 2. Florideæ.

The thallus has one or more apical cells, grows principally by apical growth, and may be differentiated into root, stem, and leaf. The chromatophores vary in form, but have a red or brownish colour, due to chlorophyll and phycoerythrin. Asexual reproduction by motionless tetraspores, which generally arise by the division into four of the contents of the tetrasporangium. The carpogonium has a trichogyne, and the carpospores, which are formed indirectly from the fertilised oosphere, possess a cell-wall.

Fig. 73.—Callithamnion elegans: a a plant with tetraspores (× 20); b apex of a branch with tetraspores(× 250).

Fig. 74.—Polysiphonia variegata: a a portion of a male plant with antheridia; b spermatia; c transverse section of thallus.

The thallus may assume very different forms. In the simplest species it is filamentous and formed of single, branched rows of cells (Callithamnion, etc., Fig. 73). Ceramium has a filamentous thallus, generally dichotomously forked (Fig. 75), or sometimes[79] pinnately branched, which, at the nodes, or throughout its entire length, is covered by a layer of small cortical cells. Polysiphonia (Fig. 74) has a filamentous, much branched thallus, made up of a central cylindrical cell, surrounded by a layer of other cells, cortical cells, which in length and position correspond to the central ones. In many of the Red Algæ the vegetative organs are differentiated into stems and leaves, the former having, as in Chara, unlimited growth in length, whilst the latter soon attain their full development. Chondrus has a fleshy, gelatinous thallus, without nodes; it is repeatedly forked into flat branches of varying thickness. Furcellaria has a forked thallus with thick branches and without nodes. The thallus of Delesseria (Fig. 76) consists of branches, often bearing leaf-like structures, with a midrib and lateral ribs springing from it. These ribs persist through the winter, and at the commencement of the succeeding period of vegetation the lateral ribs become the starting points for new leaves. In Corallina the thallus is pinnately branched, and divided into nodes and internodes. The name has been given to this genus from the fact that the thallus is incrusted with carbonate of lime to such a degree that it becomes very hard, and the[80] whole plant adopts a coral-like appearance. Other genera which are similarly incrusted, and have a leaf-like or even crustaceous thallus (such as Melobesia, Lithothamnion), are included in this family.

In some instances the cells of the thallus may be found differentiated into more or less well defined tissues, so that it is possible to find special assimilating, mechanical, and conducting tissues, the last named in some cases having the double function of conducting and of serving as a reservoir in which starch is found as a reserve material. The cells of the Florideæ, which are formed by the division of a mother-cell into two daughter-cells of unequal size, have always larger or smaller pits in the cell-walls, and the thin cell-wall separating two pits from each other is perforated by a number of small holes. These pits are particularly developed in the conducting tissues, but sieve-tubes are very rarely to be found.

Fig. 75.—Ceramium diaphanum (nat. size).

Fig. 76.—Delesseria sanguinea (about ⅓).

Tetraspores may be wanting (e.g. Lemanea) or may often arise on special, non-sexual individuals. In some (e.g. Batrachospermum) only one tetraspore is formed in each tetrasporangium, but the number is generally four, which may be formed tetrahedrally (Fig. 73) or by divisional walls perpendicular to each other, or even in a single row. The tetrasporangia in some species are free (Fig. 73), but in the majority they are embedded in the thallus.

Fig. 77.—A Lejolisia mediterranea: r haptera; s longitudinal section through a cystocarp; p the empty space left by the liberated spore (t). B-E Nemalion multifidum: a antheridia; b procarpium with trichogyne, to which two spermatia are adhering.

The sexual reproduction (discovered by Thuret and Bornet,[81] 1867) differs in the essential points from that of all other plants, and approaches most nearly to the sexual reproduction of the Bangioideæ. The sexual cells are developed from the terminal cells (never nodal cells) of the branched cell-filaments, which constitute the thallus. The mother-cells of the spermatia (spermatangia) are generally arranged in a group, in the so-called antheridia (Figs. 74, 77 A, a). On becoming ripe the membrane of the spermatangium ruptures and the spermatia emerge as spherical or ovoid, naked (a little later they may possess a cell-wall) masses of protoplasm which are not endowed with the power of motion, and hence are carried passively by the current of the water in which they may happen to be, to the female cell. This latter is analogous with the oogonium of the Green Algæ. The female reproductive organ is termed the procarpium, and consists of two parts, a lower swollen portion—the carpogonium (Fig. 77 b in A and B)—which contains the cell-nucleus, and an upper filamentous prolongation—the trichogyne (Fig. 77 B)—which is homologous with the colourless receptive spot of the oosphere of the Green Algæ, and the Porphyraceæ. In the sexual reproduction of the majority of the Florideæ, a very important part is played by certain special cells, rich in cell-contents—the auxiliary[82] cells. These are either dispersed in the interior of the thallus, or are arranged together in pairs with the cell-filament which bears the carpogonium, and are generally united with this to form an independent multicellular procarpium. The spermatia attach themselves firmly to the trichogyne and surround themselves with a cell-wall. The dividing wall at the point of contact is perforated, and the nucleus of the spermatium probably travels through the trichogyne to the swollen part of the procarpium—the carpogonium—and fuses with its nucleus. After fertilisation the trichogyne withers (Fig. 77 C), but the lower portion of the procarpium, constituting the fertilised oosphere, grows out and forms in various ways, first a tuft of spore-forming filaments known as gonimoblasts, and finally the carpospores. These latter form a new asexual generation (compare the germination of the oospore of Œdogonium and Coleochæte).

The gonimoblasts may arise in three ways:—

The Florideæ are divided into four sub-families:—

Uses. “Carragen” is the thallus of Chondrus crispus (Irish Moss) and Gigartina mamillosa. It is a common article of food on the coasts of Ireland, and swells to a jelly when cooked. It is officinal. Rhodymenia palmata is generally eaten as food in Ireland and in some places on the west coast of Norway; it is also used as food for sheep and hence is termed “Sheep-seaweed.” Agar-Agar is the jelly obtained from species of Gelidium and Gigartina growing in China and Japan.

Mode of Life. The Fungi have no chlorophyll, and are thus unable in any stage of their existence to assimilate carbon; they must therefore live as saprophytes or parasites. There is, however, no strong line of demarcation between these; many Fungi commence as true parasites, but only attain their full development upon or in dead plants or animals (Rhytisma, Empusa). Many saprophytes may occasionally appear as parasites, and are then designated “facultative parasites” (Nectria cinnabarina, Lophodermium pinastri), in contradistinction to those which only[85] appear as parasites, “obligate parasites” (Mildew, Brand-and Rust-Fungi, Cordyceps).

The parasites which live on the surface of the host-plant are termed epiphytic (Mildew, Fusicladium); and those living in its tissues are termed endophytic (Ustilago, Peronospora). Epizoic (Oidium tonsurans, Laboulbenia) and endozoic Fungi (Cordyceps, Entomophthora), are distinguished, in the same manner, as those which live on the surface or in the interior of animals. The Fungi designated pathogenic are especially those which produce disease in human beings and in animals.

Most of the diseases of plants are attributed to the parasitic Fungi. These force their way into the host-plant by piercing the outer wall of the epidermis, as in the Potato-disease; or by growing in through the stomata, e.g. the summer generations of the Rust of Wheat; or they can only penetrate through a wound, e.g. Nectria. Some effect an entrance into the host-plant by the secretion of a poisonous matter or ferment, which softens and destroys the cell-walls (Sclerotinia). Some Yeast and Mould Fungi secrete ferments (enzymes), which, for example, convert cane-sugar into a sugar capable of fermentation.

The relation of the parasitic Fungus to the host-plant is mainly of two kinds. In the one case, the cell-contents are destroyed, the protoplasm is killed, and the cellular tissue becomes discoloured and dies (Peronospora, Armillaria mellea, Polyporus); in the other case, the parasite has an irritating effect on the cellular tissue, whereby the affected organ grows more rapidly and becomes larger than normal, producing hypertrophy. Such malformations are termed Fungi-galls (Mycocecidia); in this manner “witches’ brooms” are produced by Æcidium, “pocket-plum” by Taphrina, and other deformities by Exobasidium and Cystopus candidus. This hypertrophy may either be produced by a vigorous cell-multiplication, which is most frequently the case, or by the enlargement of the individual cells (Synchytrium, Calyptospora). The relation between host and Fungus among the Lichens is of a very peculiar nature, termed “symbiosis.”

Vegetative Organs. The vegetative parts of a Fungus are termed its mycelium.[10] This is formed of a mass of long, cylindrical, branched cells resembling threads (and hence termed hyphæ), which have a continued apical growth. The mycelium, in its early development, shows a well-marked difference between the[86] two main groups of true Fungi: in the Phycomycetes, or Algal Fungi, the mycelium has no transverse walls, and is therefore unicellular, while in the Mesomycetes and Mycomycetes it is provided with dividing walls, which gradually arise during growth, in the youngest hyphæ; intercalary transverse walls may also be formed at a later period. In the hyphæ of some of the Higher Fungi (Hymenomycetes), connections may be formed between two contiguous cells of the same hypha, by a protuberance growing out from an upper cell just above the transverse wall, and forming a junction with the cell below. These are known as clamp-connections; they appear to be of use in affording communication between the two cells.

The hyphæ of Fungi, where they come in contact with one another, often grow together, so that H-formed combinations (fusions) are produced, which give rise to very compact felted tissue. When the hyphæ are not only closely interwoven, but also united and provided with many transverse walls, the mycelium assumes the appearance of a tissue with isodiametric cells, and is then termed pseudo-parenchyma. The hyphæ-walls are sometimes very much thickened, and composed of several layers, and the external layers, by the absorption of water, may often swell very much and become mucilaginous. In some instances the walls are colourless, in others coloured, the most frequent colour being brown. The cell-contents may also be coloured, and in that case are generally yellow; this colour is chiefly connected with the fat (oil) which may be found in abundance in the Fungi, whilst starch is invariably absent in all the true Fungi.

The mycelium assumes many different forms; sometimes it appears as a thread-like, cobwebby, loose tissue, less frequently as firm strands, thin or thick membranes, horn-like plates or tuber-like bodies. The thread-like mycelium may, in the parasitic Fungi, be intercellular or intracellular, according as it only extends into the interstices between the cells or enters into the cells proper. In the first case there are generally found haustoria, or organs of suction (e.g. among the Peronosporaceæ; Taphrina, on the contrary, has no haustoria); but haustoria are also found among the epiphytic Fungi (e.g. Erysiphaceæ). Intracellular mycelia are found in the Rust-Fungi, in Claviceps purpurea, Entomophthora, etc. In spite of its delicate structure, this mycelium may live a long time, owing to the circumstance that it continues to grow peripherally, while the older parts gradually die off (“fairy rings”).

[87]

String-like mycelia may be found, for example, in Phallus, Coprinus, and are formed of hyphæ, which run more or less parallel to each other. Membrane-like mycelia are chiefly to be found in Fungi growing on tree-stems (Polyporaceæ and Agaricaceæ); they may have a thickness varying from that of the finest tissue-paper to that of thick leather, and may extend for several feet. The peculiar horny or leather-like strands and plates which, for instance, appear in Armillaria mellea, are known as Rhizomorpha; they may attain a length of more than fifty feet. The tuber-like mycelia or sclerotia play the part of resting mycelia, since a store of nourishment is accumulated in them, and after a period of rest they develope organs of reproduction. The sclerotia are hard, spherical, or irregular bodies, from the size of a cabbage seed to that of a hand, internally white or greyish, with a brown or black, pseudo-parenchymatous, external layer. Sclerotia only occur in the higher Fungi, and are found both in saprophytes, e.g. Coprinus, and in parasites, e.g. Claviceps (Ergot), Sclerotinia.

Reproduction. Sexual reproduction is found only among the lower Fungi which stand near to the Algæ, the Algal-Fungi, and takes place by the same two methods as in the Algæ, namely by conjugation and by the fertilisation of the egg-cell in the oogonium.

The majority of Fungi have only ASEXUAL reproduction. The most important methods of this kind of reproduction are the sporangio-fructification and the conidio-fructification.

In the SPORANGIO-FRUCTIFICATION the spores (endospores) arise inside a mother-cell, the sporangium (Fig. 80). Spores without a cell-wall, which move in water by means of cilia and hence are known as swarmspores or zoospores, are found among the Oomycetes, the sporangia in which these are produced being called swarm-sporangia or zoosporangia (Figs. 86, 87, 91, 94).

In the CONIDIO-FRUCTIFICATION the conidia (exospores) arise on special hyphæ (conidiophores), or directly from the mycelium. When conidiophores are present, the conidia are developed upon them terminally or laterally, either in a basipetal succession (in many Fungi, for example in Penicillium, Fig. 111, Erysiphe, Cystopus), or acropetally (in which method the chains of conidia are often branched; examples, Pleospora vulgaris, Hormodendron cladosporioides). All conidia are at first unicellular, sometimes at a later stage they become two-celled or multicellular through the formation of partition-walls (Piptocephalis). The conidia with[88] thick, brown cell-walls, and contents rich in fats (resting conidia), can withstand unfavourable external conditions for a much longer period than conidia with thin walls and poor in contents.

The SPORANGIA arise either from the ordinary cells of the mycelium (Protomyces), or are borne on special hyphæ. They are generally spherical (Mucor, Fig. 80; Saprolegniaceæ), egg-, pear-, or club-shaped (Ascomycetes), more rarely they are cylindrical or spindle-shaped. While among the Phycomycetes the size, form, and number of spores are indefinite in each species, in the Ascomycetes the sporangia (asci) have a definite size, form, and number of spores. The spores of the Ascomycetes are known as ascospores.

The sporangio-fructification is found under three main forms.

1. Free Sporangiophores which are either single (Mucor, Fig. 78), or branched (Thamnidium).

2. Sporangial-layers. These are produced by a number of sessile or shortly-stalked sporangia, being formed close together like a palisade (Taphrina, Fig. 105).

3. Sporangiocarps. These consist usually of many sporangia enclosed in a covering, they are found only in the Carpoasci, and are also known as ascocarps. The parts of an ascocarp are the covering (peridium), and the hymenium, which is in contact with the inner wall of the peridium, and is generally made up of asci, and sterile, slender hyphæ. The latter either penetrate between the asci and are branched and multicellular (paraphyses, Figs. 103 d, 123, 125, 129), or clothe those parts of the inner wall which bear no asci (periphyses; among many peronocarpic Ascomycetes, e.g. Chætomium, Sordaria, Stictosphæra hoffmanni). The ascocarps are produced directly from the mycelium, or from a stroma, that is a vegetative body of various forms, in which they may be embedded (Figs. 116 B, C).

Among the conidio-fructifications there are, in the same way, three divisions.

1. Free conidiophores (Fig. 109). The form of the conidiophores, the shape, and number of its spores are various. In the most highly developed Fungi, the Basidiomycetes, there are, however, special more highly developed conidiophores, the basidia, which have a definite form and spores of a definite shape and number. The conidia borne on basidia are called basidiospores.

2. Conidial-layers. (a) The SIMPLEST case of this is found when the conidiophores arise directly from the mycelium, parallel[89] to one another, and form a flat body (e.g. Exobasidium vaccinii, Hypochnus; among the Phycomycetes, Empusa muscæ and Cystopus). (b) In a HIGHER form the conidial-layers are thick, felted threads (stroma) inserted between the mycelium and the hymenium (i.e. the region of the conidiophores). Examples are found in a section of the Pyrenomycetes (Fig. 122). (c) The HIGHEST form has the basidial-layer, that is a conidial-layer with more highly developed conidiophores (basidia). The basidial-layer, with stroma, and the hymenium (region of the basidia), forms the basidio-fructification, which is branched in the Clavariaceæ, and hat-shaped in other Hymenomycetes (in these groups the hymenium is confined to the lower side of the pileus).

The hymenium of the conidial-layer and basidial-layer is composed entirely of conidiophores, or of conidiophores and sterile hyphæ (paraphyses) which are probably always unicellular. Paraphyses are found in Entomophthora radicans, and in certain Basidiomycetes (e.g. Corticium).

3. Conidiocarps (pycnidia). A special covering surrounds the conidia-forming elements. The inner side of this covering (peridium) bears the hymenium, i.e. those elements from which the conidia are abstricted. The conidiocarps arise either immediately from the hyphæ or from a stroma in which they are generally embedded. Conidiocarps are entirely wanting in the Phycomycetes. On the other hand they are found among the Ascomycetes and Basidiomycetes, and in the latter group the conidiocarps contain more highly differentiated conidiophores (basidia) and are known as basidiocarps. Conidiocarps with simple conidiophores, are found only among the Basidiomycetes, in the Uredinaceæ, and in Craterocolla cerasi. In the Ascomycetes (Figs. 120 d, e; 117 a, b; 123 a; 124 b) the conidiocarps are visible, as points, to the naked eye, while the basidiocarps of the Basidiomycetes (Figs. 170, 171, 173–176, 178–180) vary from the size of a pea to that of a child’s head. The “spermogonia” of the Ascomycetes and Lichenes, are conidiocarps with small conidia (microconidia) which germinate sometimes more slowly than other conidia, and formerly were erroneously considered as male reproductive cells, and called spermatia.

The conidia of the Fungi are not primitive structures. The comparison of the sporangia and conidia among the Zygomycetes, and among the species of the genus Peronospora shows, that the conidia are aberrant formations, and that they have arisen through[90] the degeneration of the sporangium, which, by the reduction of its spores to one, has itself become a spore.

The reproduction of Fungi is accomplished not only by spores and conidia, but also sometimes by chlamydospores. These are fundaments[11] of sporangiophores and conidiophores, which have taken on a resting condition in the form of a spore, and are able to germinate and produce carpophores. In the formation of the chlamydospores the hyphæ accumulate reserve materials at the expense of the neighbouring cells; in the undivided hyphæ of the Phycomycetes transverse walls are formed, and finally the chlamydospores are set free by the decay of the empty cells connecting them with the mycelium. One must distinguish between oidia and true chlamydospores. The former are more simple, the latter are a somewhat more differentiated form of carpophore fundaments, which serve for propagation in the same manner as spores. In Chlamydomucor racemosus the chlamydospores grow out into the air and form differentiated carpophores. In the Autobasidiomycetes they only germinate vegetatively, and not with the formation of fructifications. From Chlamydomucor up to the Autobasidiomycetes the successive development of the fructification,[91] which is interrupted by the formation of the chlamydospores, degenerates more and more. Among certain Ustilagineæ the chlamydospores (brand-spores) no longer germinate with the production of fructifications. In the Uredinaceæ, only one of the three chlamydospore-forms has the property of producing fructifications on germination; the other forms only germinate vegetatively, like ordinary spores, and in the same manner as the chlamydospores of the Autobasidiomycetes. In the Hemibasidii, and the Uredinaceæ, in Protomyces, the chlamydospores are the chief means of reproduction. They are found also among the Ascomycetes.

The sporangia and the conidia of the Fungi have their common origin in the sporangia of the Phycomycetes. The asci (and the Ascomycetes which are characterised by these bodies) are descended from the sporangia-forming, lower Fungi; the basidia (and the Basidiomycetes) from those which bear conidia. The sporangia of the Phycomycetes are the primitive form and the starting point for all the reproductive forms of the Fungi. The chlamydospores appear besides in all classes of Fungi as supplementary forms of reproduction, and are of no importance in determining relationships. Although the expression “fruit” must essentially be applied to true Phanerogams, yet, through usage, the term “fruit-forms,” is employed to designate the forms or means of reproduction of Fungi, and the organs of reproduction are known as organs of fructification, the sporangiophores and conidiophores as fruit-bearers (carpophores), and the sporangiocarps, conidiocarps, and basidiocarps as “fruit-bodies.”

The liberation and distribution of the spores and conidia. The spores and conidia, on account of their small size and lightness, are spread far and wide by currents in the air, but in addition to this method, insects and other animals frequently assist in disseminating them. The liberation of the conidia is occasionally effected by the complete shrinking away of the conidiophore, but more frequently by abstriction from the conidiophores, either by their gradually tapering to a point, or by the[92] dissolution of a cross-wall (generally of a mucilaginous nature). The individual links of conidia-chains are detached from one another in the same way, or often by means of small, intercalary cells, which are formed at the base of the individual links, and becoming slimy, dissolve upon the maturity of the spores. Special contrivances for ejecting the spores and conidia may often be found. In Peronospora the cylindrical fruit-hyphæ in the dry condition become strap-shaped and also twisted. These are very hygroscopic, and the changes of form take place so suddenly, that the spores are violently detached and shot away. In Empusa a peculiar squirting mechanism may be found (Fig. 85). Each club-shaped hypha which projects from the body of the fly, bears a conidium at its apex; a vacuole, which grows gradually larger, is formed in the slimy contents of the hypha, and the pressure thereby eventually becomes so great that the hypha bursts at its apex, and the conidium is shot into the air. By a similar mechanism, the spores of many of the Agaricaceæ are cast away from the parent-plants. In the case of Pilobolus (Fig. 84) the entire sporangium is thrown for some distance into the air by a similar contrivance, the basal region of the sporangium having, by the absorption of water, been transformed into a slimy layer which is readily detached. Sphærobolus, a Gasteromycete, has a small, spherical fruit-body (basidiocarp), the covering of which, when ripe, suddenly bursts, and the basidiospores contained in it are forcibly ejected.

The spores which are enclosed in asci are, in some instances, set free from the mother-cell (ascus) prior to their complete development (Elaphomyces, Eurotium). In the case of the majority of the Pyrenomycetes and Truffles, the asci swell by the absorption of water into a slimy mass, which gradually disappears, so that the spores lie free in the fruit-body; they either remain there till the fruit-body decays, as in those which have no aperture (Perisporiaceæ, Tuberaceæ), or the slimy mass, by its growth, is forced out through the aperture of the sporocarp, taking the spores with it (Nectria). The ejection of the spores by mechanical means takes place in a number of Ascomycetes, and should many spores be simultaneously ejected, a dust-cloud may be seen with the naked eye to arise in the air from the fruit-body. This is the case in the larger species of Peziza, Helvella, Rhytisma, when suddenly exposed to a damp current of air. A distinction is drawn between a simultaneous ejection of all the spores contained in the ascus, and an ejection at[93] intervals (successive), when only one spore at a time is thrown out. The first of these methods is the most frequent, and is brought about by the ascus being lined with a layer of protoplasm, which absorbs water to such a degree that the elastic walls are extended at times to double their original size. The spores are forced up against the free end of the ascus, a circular rupture is made at this point, and the elastic walls contract, so that the fluid with the spores is ejected. Special means may in some instances be found to keep the spores together, and compel their simultaneous ejection. Thus, a tough slime may surround all the spores (Saccobolus), or a chain-apparatus, similarly formed of tough slime; or there may be a hooked appendage from each end of the spores which hooks into the appendage of the next spore (Sordaria). The paraphyses occurring between the asci in many Ascomycetes, also play a part in the distribution of the spores, by reason of the pressure they exercise. The asci in some of the Pyrenomycetes, which are provided with jar-shaped fruit-bodies, elongate to such an extent that, without becoming detached from their bases, they reach the mouth of the fruit-body one at a time, burst and disperse their spores, and so make room for those succeeding. An ejection of the spores at intervals from the ascus is rarer. It takes place, for instance, in Pleospora, whose asci have a double wall. The external wall, by absorption of water, at last becomes ruptured, and the internal and more elastic membrane forces itself out in the course of a few seconds to one of two or three times greater length and thickness, so that one spore after another is forcibly ejected from a narrow aperture at the end of the ascus.

Germination of spores (conidia and chlamydospores). In many spores may be found one or more germ-pores, i.e. thinner places, either in the inner membrane (uredospores, Sordaria) or in the external membrane (teleutospores in Rust-Fungi), through which the germination takes place. Generally this does not occur till the spores have been set free: in some Ascomycetes germination commences inside the ascus (Taphrina, Sclerotinia). The different ways in which the spores germinate may be classified into three groups.

I. The ordinary germination occurs by the spore emitting a germ-tube, which immediately developes into a mycelium. In spores with a double wall it is only the inner membrane which forms the germ-tube. In swarmspores a single wall is formed after the withdrawal of the cilia, and this, by direct elongation,[94] becomes the germ-tube. The protoplasm accumulated in the spore enters the hypha, which, in pure water, can only grow as long as the reserve nourishment lasts.

2. Germination with promycelium differs only by the circumstance that the hypha developed from the germ-tube has a very limited growth, and hence it does not immediately develope into a mycelium, but produces conidia (Rust-and Brand-Fungi). This promycelium must only be regarded as an advanced development of a conidiophore or basidium.

3. The yeast-formation of conidia consists in the production of outgrowths, very much constricted at their bases, from one or more places. Each of the conidia formed in this manner may again germinate in the same way. When sufficient nourishment is present, a branched chain of such conidia is formed, and these are finally detached from one another. Yeast-like buddings from the conidia are produced in various Fungi, e.g. Ascoidea, Protomyces, Ustilagineæ, Ascomycetes, Tremellaceæ, etc. In the Ustilagineæ these conidia are an important element in the development. The budding conidia of Exobasidium forms a “mould” on the nutritive solution. The yeast-like conidia are not to be confounded with the “Mucor-yeast” (comp. Mucoraceæ). For Saccharomyces see Appendix to the Fungi, page 176.

In a compound spore (i.e. when a mass of spores are associated together) each spore germinates on its own account. There are sometimes, however, certain among them which do not germinate, but yield their contents to those which do.

The length of time for which conidia can retain their power of germination is shortest (being only a few weeks) in those having thin walls and containing a large supply of water (Peronosporaceæ, Uredinaceæ). In many spores a resting period is absolutely necessary before they are able to germinate (resting spores). It has been observed in some spores and conidia, that the faculty of germinating may be preserved for several years if the conditions necessary for germination remain absent (Ustilagineæ, Eurotium, Penicillium).

The optimum, minimum and maximum temperatures required for the germination of the spores has been decided in the case of a good many Fungi. A large portion of the most common Fungi have their optimum at 20°C., minimum at 1–2°C, maximum at 40°C. In the case of pathogenic Fungi the optimum is adapted to the temperature of the blood. Fungi living in manure, whose[95] spores are often adapted to germinate in the alimentary canals of warm-blooded animals, have an optimum corresponding to the temperature of these animals, but with a little margin.

Systematic Division.—The lowest class of the Fungi is that of the Phycomycetes, which have an unicellular mycelium, sexual and asexual reproduction, and have doubtless sprung from sporangia-bearing, lower Green Algæ. From the Phycomycetes (and certainly from the Zygomycetes) spring two well defined branches, each with numerous distinct species; to the one branch belong the Hemiasci and the Ascomycetes, to the other the Hemibasidii and the BASIDIOMYCETES. Ascomycetes and Basidiomycetes may be united under the title of Mycomycetes or Higher Fungi. The Hemiasci and the Hemibasidii constitute the class of Mesomycetes. The Hemiasci are an intermediate form between Zygomycetes and Ascomycetes; the Hemibasidii a similar group between the Zygomycetes and Basidiomycetes. Mesomycetes and Mycomycetes have only asexual reproduction; sexual reproduction is wanting. Their mycelium is multicellular.

Up to the present time about 39,000 species have been described.

Review of the divisions of the Fungi:—

Class I.—Phycomycetes (Algal-Fungi).

• Sub-Class 1. Zygomycetes.
• Sub-Class 2. Oomycetes.
• Family 1. Entomophthorales.
• Family 2. Chytridiales.
• Family 3. Mycosiphonales.

Class II. Mesomycetes.

• Sub-Class 1. Hemiasci.
• Sub-Class 2. Hemibasidii (Brand-Fungi).

Class III.—Mycomycetes (Higher Fungi).

• Sub-Class 1. Ascomycetes.
• Series 1. Exoasci.
• Series 2. Carpoasci.
• Family 1. Gymnoascales. }
• Family 2. Perisporiales. }Angiocarpic Exoasci.
• Family 3. Pyrenomycetes. }
• Family 4. Hysteriales. }
• Family 5. Discomycetes. } Hemiangiocarpic Exoasci.
• Family 6. Helvellales. Gymnocarpic (?) Exoasci.
• Additional: Ascolichenes. Lichen-forming Ascomycetes.[96]
• Sub-Class 2. Basidiomycetes.
• Series 1.—Protobasidiomycetes. Partly gymnocarpic, partly angiocarpic.
• Series 2. Autobasidiomycetes.
• Family 1. Dacryomycetes. Gymnocarpic.
• Family 2. Hymenomycetes. Partly gymnocarpic, partly hemiangiocarpic.
• Family 3. Phalloideæ. Hemiangiocarpic.
• Family 4. Gasteromycetes. Angiocarpic.
• Additional: Basidiolichenes. Lichen-forming Basidiomycetes.
• Additional to the Fungi: Fungi Imperfecti. Incompletely known (Saccharomyces, Oidium-forms, etc.).

Class 1. Phycomycetes (Algal-Fungi).[12]

This group resembles Vaucheria and the other Siphoneæ among the Algæ.

Organs of Nutrition. The mycelium is formed of a single cell, often thread-like and abundantly branched (Fig. 78). Vegetative propagation by chlamydospores and oidia. Asexual reproduction by endospores (sometimes swarmspores) and conidia. Sexual reproduction by conjugation of two hyphæ as in the Conjugatæ, or by fertilisation of an egg-cell in an oogonium. On this account the class of the Phycomycetes is divided into two sub-classes: Zygomycetes and Oomycetes.

Sub-Class I. Zygomycetes.

Sexual reproduction takes place by zygospores, which function as resting-spores, and arise in consequence of conjugation (Fig. 81); in the majority of species these are rarely found, and only under special conditions. The most common method of reproduction is by endospores, by acrogenous conidia, by chlamydospores, or by oidia. Swarmspores are wanting. Parasites and saprophytes (order 6 and 7). The zygospores are generally produced when the formation of sporangia has ceased; e.g. by the suppression of the sporangial-hyphæ (Mucor mucedo), or by the diminution of oxygen; Pilobolus crystallinus forms zygospores, when the sporangia are infected with saprophytic Piptocephalis or Pleotrachelus.

A. Asexual reproduction only by sporangia.

Order 1. Mucoraceæ. The spherical sporangia contain many spores. The zygospore is formed between two unicellular branches (gametes).

[97]

The unicellular mycelium (Fig. 78) of the Mucoraceæ branches abundantly, and lives, generally, as a saprophyte on all sorts of dead organic remains. Some of these Fungi are known to be capable of producing alcoholic fermentation, in common with the Saccharomyces. This applies especially to Chlamydomucor racemosus (Mucor racemosus), when grown in a saccharine solution, and deprived of oxygen; the mycelium, under such conditions, becomes divided by transverse walls into a large number of small cells. Many of these swell out into spherical or club-shaped cells, and when detached from one another become chlamydospores, which abstrict new cells of similar nature (Fig. 79). These chlamydospores were formerly erroneously termed “mucor-yeast,” but they must not be confounded with the yeast-conidia (page 94). They are shortened hyphæ, and are not conidia of definite size, shape, and point of budding. Oidia are also found in Chlamydomucor.

Fig. 78.—Mucor mucedo. A mycelium which has sprung from one spore, whose position is marked by the *: a, b, c are three sporangia in different stages of development; a is the youngest one, as yet only a short, thick, erect branch; b is commencing to form a sporangium which is larger in c, but not yet separated from its stalk.

[98]

The Mucoraceæ, in addition to the chlamydospores and oidia, have a more normal and ordinary method of reproduction; viz., by spores which are formed without any sexual act. Mucor has round sporangia; from the mycelium one or more long branches, sometimes several centimetres in length, grow vertically into the air; the apex swells (Figs. 78, 80) into a sphere which soon becomes separated from its stalk by a transverse wall; in the interior of this sphere (sporangium) a number of spores are formed which eventually are set free by the rupture of the wall. The transverse wall protrudes into the sporangium and forms the well-known columella (Fig. 80 d, e). The formation of spores takes place in various ways among the different genera.

Fig. 79.—Chlamydospores of Chlamydomucor racemosus (× 375 times.)

Fig. 80.—Mucor mucedo: a a spore commencing to germinate (× 300 times); b a germinating spore which has formed a germ-tube from each end (× 300 times); c the apex of a young sporangium before the formation of spores has commenced; the stalk is protruded in the sporangium in the form of a column: on the wall of the sporangium is found a very fine incrustation of lime in the form of thorn-like projections; d a sporangium in which the formation of spores has commenced; e a sporangium, the wall of which is ruptured, leaving a remnant attached to the base of the columella as a small collar. A few spores are seen still adhering to the columella.

Sexual Reproduction by conjugation takes place in the following manner. The ends of two hyphæ meet (Fig. 81) and become more or less club-shaped; the ends of each of these are cut off by a cell-wall, and two new small cells (Fig. 81 A) are thus formed, these coalesce and give rise to a new cell which becomes the very thick-walled zygote (zygospore), and germinates after[99] period of rest, producing a new hypha, which bears a sporangium (Fig. 81 E).

Mucor mucedo, Pin-mould, resembles somewhat in appearance Penicillium crustaceum and is found growing upon various organic materials (bread, jam, dung, etc.).

Pilobolus (Figs. 83, 84) grows on manure. Its sporangium (Fig. 84 a″) is formed during the night and by a peculiar mechanism (page 92) is shot away from the plant in the course of the day. This generally takes place in the summer, between eight and ten a.m. The sporangium is shot away to a height which may be 300 times greater than that of the plant itself, and by its stickiness it becomes attached to portions of plants, etc., which are in the vicinity. If these are eaten by animals, the spores pass into the alimentary canal and are later on, sometimes even in a germinating condition, passed out with the excrement, in which they form new mycelia.

Phycomyces nitens (“Oil-mould”) is the largest of the Mould Fungi; its sporangiophores may attain the height of 10–30 c.m.

Order 2. Rhizopaceæ. Rhizopus nigricans (Mucor stolonifer) which lives on decaying fruits containing sugar, on bread, etc., has, at the base of the sporangiophores, tufts of rhizoids, i.e. hyphæ, which function as organs of attachment. From these, “runners” are produced which in a similar manner develope sporangiophores and rhizoids.

Figs. 81, 82.—Mucor mucedo: A-C stages in the formation of the zygote; D zygote; E germination of zygote: the exospore has burst, and the endospore grown into a hypha bearing a sporangium.

Order 3. Thamnidiaceæ. On the same sporangiophore, in addition to a[100] large, terminal, many-spored sporangium, many smaller, lateral sporangia are formed with a few spores. Thamnidium.

B. Asexual reproduction by sporangia and conidia.

Order 4. Choanephoraceæ. Choanephora with creeping endophytic mycelium, and perpendicular sporangiophores.

Order 5. Mortierellaceæ. Mortierella polycephala produces on the same mycelium conidia and sporangiophores. M. rostafinskii has a long stalked sporangiophore, which is surrounded at its base by a covering of numerous felted hyphæ.

Fig. 83.—Pilobolus. Mycelium (a, a), with a sporangiophore (A) and the fundament of another (B).

Fig. 84.—Pilobolus. Sporangium (a″) with stalk (a-c), which is covered by many small drops of water pressed out by turgescence.

C. Asexual reproduction only by conidia.

Order 6. Chætocladiaceæ. The conidia are abstricted singly and acrogenously. Chætocladium is a parasite on the larger Mucoraceæ.

Order 7. Piptocephalidaceæ. The conidia are formed acrogenously and in a series, by transverse divisions. The zygospore arises at the summit of the conjugating hyphæ, which are curved so as to resemble a pair of tongs. Piptocephalis and Syncephalis live parasitically on the larger Mucoraceæ.

Sub-Class 2. Oomycetes.

Sexual reproduction is oogamous with the formation of brown, thick-walled oospores which germinate after a period of rest. Asexual reproduction by conidia and swarmspores. Parasites, seldom saprophytes.

The oospores are large spores which are formed from the egg-cell (oosphere) of the oogonium (oosporangium, Fig. 89, 95). A branch of the mycelium attaches itself to the oogonium and forms at its apex the so-called “antheridium” (pollinodium[13]): this sends one or more slender prolongations (fertilising tubes) through the wall of the oogonium to the egg-cell.

[101]

Fig. 85.—Empusa muscæ (Fly-mould). I. A fly killed by the fungus, surrounded by a white layer of conidia. II. The conidiophores (t) projecting from the body of the fly. Some of the conidia, a few of which have developed secondary conidia, are attached to the hairs (mag. 80 times). III. A perfect hypha. IV. A hypha in the act of ejecting a conidium (c), enveloped in a sticky slime (g). V. A conidium which has developed a secondary conidium (sc). VI. A branched hypha produced by cultivation. VII. A secondary conidium which has produced a small mycelium (m). VIII. A conidium germinating on the fly’s body. IX. Mycelium. X. Conidia germinating like yeast in the fatty tissue of the fly. (III.-VII. and IX. magnified 300 times; VIII. and X. magnified 500 times.)

A. Asexual reproduction by conidia only.

Family 1. Entomophthorales.

The mycelium is richly branched. The family is a transitional step to the conidia-bearing Zygomycetes, since the oospores of many members of this family arise, and are formed, like zygospores.

Order 1. Entomophthoraceæ. Mycelium abundantly developed. This most frequently lives parasitically in living insects, causing their death. The conidiophores forming the conidial-layer project from the skin, and abstrict a proportionately large conidium which is ejected with considerable force, and by this means transferred to other insects. These become infected by the entrance of the germ-tube into their bodies. The spherical, brown resting-spores develope inside the bodies of insects and germinate by emitting a germ-tube.

B. Asexual reproduction by zoospores or conidia.

Family 2. Chytridiales.

In this family the mycelium is very sparsely developed or is wanting. The entire plant consists principally or entirely of a[103] single zoosporangium whose zoospores have generally one cilium. The resting-spores arise either directly from the zoosporangium, which, instead of forming zoospores, surrounds itself by a thick cell-wall; or they are formed by the conjugation of two cells (in which case they are spoken of as oospores). Microscopic Fungi, parasitic on water plants (especially Algæ) or small aquatic animals, seldom on land plants.

Order 1. Olpidiaceæ. Without mycelium. Swarmspores and resting-spores.

Fig. 86.—Chytridium lagenula. Zoosporangium a before, b after the liberation of the swarmspores.

Fig. 87.—Obelidium mucronatum: m mycelium; s swarmspores.

Order 2. Rhizidiaceæ. Mycelium present. Zoospores and resting-spores.

Order 3. Zygochytriaceæ. Mycelium present. Zoospores and oospores. The latter are the product of the conjugation of two cells (Fig. 88).

[104]

Family 3. Mycosiphonales.

The mycelium is bladder-like or branched. Zoospores. Sexual reproduction by oospores, which are produced in oogonia. The latter are fertilised, in some forms, by the antheridium.

Order 2. Peronosporaceæ. Almost entirely parasites. The unicellular, often very long and abundantly branched mycelium lives in the intercellular spaces of living plants, especially in the green portions, and these are more or less destroyed and deformed in consequence. Special small branches (suction-organs, “haustoria”) are pushed into the cells in order to abstract nourishment from them. Both oospores and conidia germinate either immediately, or they develope into sporangia with swarmspores, having always two cilia. Only one oospore is formed in each oogonium; its contents (Fig. 89) divide into a centrally placed egg-cell and the “periplasm” surrounding it; this is of a paler colour and on the maturity of the oospore forms its thick, brown, external covering.

Fig. 88.—Polyphagus euglenæ. A with smooth, B with thorny oospores; m and f the two conjugating cells.

Fig. 89.—Peronospora alsinearum. Mycelium with egg-cell and antheridium.

Fig. 90.—Phytophthora infestans (strongly magnified). Cross section through a small portion of a Potato-leaf (the under side turned upwards): a the mycelium; b b two conidiophores projecting through a stoma; c conidia; e the spongy tissue of the leaf; g the epidermis.

The Potato-fungus (Phytophthora infestans) is of great interest. Its thallus winters in the Potato-tuber; other organs for passing the winter, such as oospores, are not known. When the tuber germinates, the Fungus-hyphæ penetrate the young shoot and keep pace with the aerial growth and development of the plant. The conidiophores emerge through the stomata, especially on the under side of the leaves; they branch like a tree (Fig. 90), and[105] appear to the naked eye as a fine mould on the surface of the plant. The disease soon makes itself known by the brown colouring of those parts of the plant which are attacked, and by their withering. An ovoid conidium arises at first by the formation of a dividing wall at the apex of each branch of the conidiophore[106] (Fig. 90 c c), and immediately underneath it another is formed, which pushes the first to one side, and so on. These conidia sometimes germinate directly, and form a mycelium, but most frequently their protoplasm divides into many small masses, each of which becomes a pear-shaped zoospore provided with two cilia (Fig. 91). Water is required for their germination, and when the ripe conidia are placed in a drop of water the swarm-cells are formed in the course of about five hours. They swarm about in rain and dewdrops in the Potato-fields, and are carried with the water to the Potato-plants and to the tubers in the soil. The wind also very easily conveys the conidia to healthy Potato-fields and infects them. The enormous quantity of conidia and swarm-cells that may be formed in the course of a summer explains the rapid spreading of the disease; and the preceding makes it clear why wet summers are favourable to its existence. When the swarm-cells germinate, they round off, and then surround themselves with a cell-wall which grows out into the germ-tube, and pierces through the epidermis of the host-plant (Fig. 92). Having entered the host, a new mycelium is formed. The potato disease, since 1845, has been rampant in Europe; it has, no doubt, been introduced from America, which, it must be remembered, is the home of the Potato-plant.

Fig. 91.—Phytophthora infestans: a-c conidia detached; in c the swarm-cells are leaving the mother-cell; d two free-swimming swarm-cells.

Fig. 92.—Phytophthora infestans. Cross section through a portion of a Potato-stalk. Two germinating conidia (a, b) piercing the epidermis, and the mycelium penetrating the cells.

Fig. 93.—A fly overgrown with Saprolegnia.

Fig. 94.—Formation of swarmspores in a Saprolegnia: a germinating swarmspores.

Order 3. Saprolegniaceæ, Water-Fungi which live as saprophytes on organic remains lying in water, for instance, on dead flies (Fig. 93), worms, remains of plants; but they may also make their appearance on living animals, being frequently found, for example, on the young trout in rearing establishments.

Fig. 95.—Oogonium with two antheridia, Achlya racemosa.

The thallus is a single, long and branched cell. It has one portion which serves as root, and lives in the substratum, where it ramifies abundantly for the purpose of absorbing nourishment; and another portion projecting freely in the water, and sending out hyphæ on all sides (Fig. 93). The asexual reproduction takes place by swarmspores (Fig. 94), which are developed in large sporangia; these swarmspores generally possess two cilia, and on germination grow into new plants. The entire protoplasm[108] in the oogonium is formed into one or more oospheres, without any surrounding “periplasm.” The oospheres may not be fertilised (p. 100), and then develope parthenogenetically.

Class 2. Mesomycetes.

The Mesomycetes are intermediate forms between the Phycomycetes and the Higher Fungi. In the vegetative organs, and in the multicellular hyphæ, they resemble the Higher Fungi; the methods of reproduction, however, show the characters of the Phycomycetes, namely sporangia and conidiophores of varying size and with varying number of spores; definite and typically formed asci and basidia are not present. Sexual reproduction is wanting. The Hemiasci are transitional between the Phycomycetes and the Ascomycetes, the Hemibasidii (Brand-Fungi) form the transition to the Basidiomycetes.

Sub-Class 1. Hemiasci.

The Hemiasci are Fungi with sporangia which, although resembling asci, yet have not, however, a definite form and a definite number of spores. Besides endospores, conidia, chlamydospores and oidia are found.

This order, by reason of the covering of the sporangia, forms the transition from the Hemiasci to the Carpoasci, while the two first supply an intermediate step to the Exoasci.

Sub-Class 2. Hemibasidii, Brand-Fungi.

The Brand-Fungi (also known as Ustilagineæ) are Fungi with basidia-like conidiophores, which, however, have not yet advanced to a definite form or number of conidia. They are true parasites, whose mycelium spreads itself in the intercellular spaces of Flowering plants. The mycelium is colourless, quickly perishable, has transverse walls at some distance from each other (Fig. 96), and sends out haustoria into the cells of the host-plant.

Fig. 96.—Entyloma ranunculi. 1. Cross section of a portion of a leaf of Ficaria permeated by the mycelium; a bundle of hyphæ with conidia emerging from a stoma; in one of the cells are found four brand-spores. 2. A brand-spore developed in the middle of a hypha.

It most frequently happens that the germ-tube enters the host-plant at its most tender age, that is, during the germination of the seed; the mycelium then wanders about in the tissues of the shoot[110] during its growth, until it reaches that part of the plant where the spores are to be formed. The spore-formation takes place in the same way in all those species whose brand-spores are developed in the floral parts of the host-plant. Many Brand-Fungi have, however, a more local occurrence, and the mycelium is restricted to a smaller area of the leaf or stem. Those organs of the host-plant in which the brand-spores are developed often become strongly hypertrophied. In perennial plants the mycelium winters very often in the rhizome.

Fig. 97.—Doassansia alismatis. 1. A fruit-body, formed by a covering of oblong hyphæ, which encloses a mass of brand-spores, and is embedded in the leaf-tissue of the host-plant; 20 times natural size. 2. A germinating brand-spore, 500 times natural size. 3. Three connected resting-spores, 400 times natural size. 4. Two conidia grown together, 600 times natural size.

The brand-spores are the winter resting-spores of the Brand-Fungi. They arise in the tissues of the host-plant, which is often destroyed, and become free through the rupture of the epidermis; they are thick-walled, generally brown or violet, and very often possess warts, spines, or reticulate markings. Fruit-bodies, that is enclosed organs of reproduction, are found in few genera (Sphacelotheca, Graphiola; Doassansia, Fig. 97). In Tolyposporium, Tuburcinia, Thecaphora (Fig. 102), etc., the brand-spores are united into a ball of spores. On germination the brand-spores behave as chlamydospores, namely, as the fundament of conidiophores, by emitting a short germ-tube, i.e. a conidiophore (“promycelium”). The Ustilaginaceæ (Fig. 99, 2) have a short transversely divided conidiophore, with laterally developed conidia (comp. the basidia of the Protobasidiomycetes). The conidiophores of the Tilletiaceæ are undivided (unicellular promycelia), and bear the conidia terminally, and so resemble the basidia of the Autobasidiomycetes.

[111]

Fig. 98.—Tuburcinia. 1. T. trientalis. Hyphæ, some of which bear conidia at the apex, forcing themselves out between the epidermal cells on the under side of the leaf; 320 times natural size. 2. T. trientalis. A ball of spores in which some of the individual brand-spores are about to germinate; 520 times natural size. 3. T. primulicola: various forms of conidia (500 times natural size).

Fig. 99.—Ustilago. 1. Formation of brand-spores. 2. Germinating brand-spore of U. perennans. 3. Germinating brand-spore of U. cardui (after Brefeld). 4. U. filiformis. a A brand-spore with developed basidium; b another, with a conidium; c with two conidia; d with two conidia placed diametrically opposite to each other; e, detached conidia which are growing into hyphæ.

Fig. 100.—Tilletia tritici: a an ear of Wheat in which all the grains are attacked by Stinkbrand; b a blighted corn surrounded by the chaff; c a blighted corn grown together with a stamen; d the same cut across; e a brand-spore; f, g, h germinating brand-spores; i germinating conidia; j the mycelium; k-k brand-spore-forming mycelium-threads. (c-h magnified 400 times; i-k 300 times.)

[112]

Fig. 101.—Urocystis. 1, U. covalloides. A spore-ball, magnified 450 times. 2–4, U. anemones: 2–3, brand-spores which are about to germinate (magnified 450 times). 4, Conidia, the two in a state of fusion, a third with vacuoles and division-wall, magnified 500 times.

Fig. 102.—Thecaphora. 1, T. convolvuli, a ball of spores, one of the brand-spores has emitted a septate branched conidiophore (× 520). 2, T. affinis, a ball of spores (× 520).

Class 3. Mycomycetes, Higher Fungi.

The Mycomycetes are not entirely aquatic in habit; they have hyphæ with transverse walls, but no sexual reproductive organs. The asexual reproduction takes place in very different ways; by endospores (in asci), conidia, basidiospores, chlamydospores, and oidia. Swarmspores are never found.

Two chief methods of reproduction may be distinguished, and hence the class may be divided into two large sub-classes:—the Ascomycetes (with asci), and the Basidiomycetes (with basidia).

Sub-Class 1. Ascomycetes.

The main characteristic which distinguishes the Ascomycetes is the ascus; a name given to a sporangium of a definite shape and size, and containing a definite number of spores. The shape is[115] generally club-like or spherical, the number of spores 8 (in some 2, 4, 16 or more), see Figs. 103, 105, 108, 110, 113, 116, 120, 121, 123, 129.

In the lowest forms, the Exoasci, the ascus springs directly from the mycelium without the formation of a fruit-body (i.e. ascocarp). In the higher forms, which contain many species, the Carpoasci, the asci are united and form ascocarps which may be more or less enclosed (angiocarpic, hemiangiocarpic, and probably gymnocarpic).

Fig. 103.—Endogenous formation of spores in Peziza confluens. In the youngest asci there is only one nucleus (b, e); this divides into two (f); and the division is repeated so that there are 4 nuclei in c and 8 in g. These surround themselves with protoplasm and a cell-wall (h, i). The protoplasm of the mother-cell is not entirely used up.

The hyphæ of the Mycelium in some remain free, in others they are felted together and form thick strands or flat, cushion-like bodies (compare in particular the stromata of the Pyrenomycetes). Some species form sclerotia (Figs. 116, 128).

Asexual reproduction by means of conidia is known in many species as the principal means of reproduction, and the one which affords the most rapid means of distribution. The conidia may be produced on conidiophores (Fig. 109), in conidial-layers (Fig. 122), and often in conidiocarps (pycnidia, Figs. 120 d, e;[116] 123 a; 124 b.). These last occur partly as the so-called “spermogonia” (that is, pycnidia with microconidia). The conidiophores never approach the basidia.

Sometimes chlamydospores and oidia also appear in the Ascomycetes; on germination, however, they do not, as in Protomyces, form sporangia, and on this account cannot be distinctly distinguished from conidia.

The asci are morphologically the highest form of reproduction and are always found at the close of the development of these Fungi; the accessory forms of reproduction are first developed, but a well-defined alternation of generations does not occur.

Series 1. Exoasci.

Ascomycetes with FREE ASCI; sometimes also conidia, chlamydospores and oidia. One order.

Order. Taphrinaceæ. Of the genera belonging to this order, Taphrina, Endomyces, and Ascocorticium, the first is most important.

[117]

The species of Taphrina are parasites, whose free asci may be found in great numbers, generally closely pressed together, on the parts of plants which they have attacked. The asci are developed directly from the ascogenous cells of a fertile, generally sub-cuticular, hypha, which arises from the sterile mycelium. The latter arises from the germinating ascospore, and may hibernate in the tissues of its host, particularly in the winter buds, and then with the commencement of the next period of vegetation it continues its growth side by side with that of its host. The hyphæ ramify in the intercellular spaces or beneath the cuticle, but have no haustoria. The ascospores (Fig. 105 A) and unripe asci may produce conidia.

Fig. 104.—Taphrina (Exoascus) pruni. Yeast-like budding of a germinating spore (× 600).

Fig. 105.—Taphrina betulina: a ascus filled with conidia; b germinating spores (× 600).

Fig. 106.—Taphrina alni incanæ on the Alder (nat. size).

Series 2. Carpoasci.

The Carpoasci are Ascomycetes, whose asci are enclosed in fruit-bodies, i.e. ascocarps. The accessory means of reproduction are free conidiophores (Fig. 109), conidial-layers (Fig. 122), conidiocarps (Fig. 120 D, E, etc.), chlamydospores and oidia.

For the different methods of distributing the ascospores, see p. 92.

Of the six families of the Carpoasci, the first three—Gymnoascales, Perisporiales, and Pyrenomycetes—are ANGIOCARPIC (that is, the ascocarp remains closed throughout its existence, and does not dehisce when ripe); the fourth and fifth families (Hysteriales and Discomycetes), on the other hand, are HEMIANGIOCARPIC (the ascocarp, here also called an apothecium, is closed in the early stages, but opens at the commencement of ripening and exposes a hymenium of crowded asci); the family of Helvellales has probably GYMNOCARPIC (or hemiangiocarpic) fruit-bodies.

Family 1. Gymnoascales.

The ascocarps are surrounded by a spongy and incomplete envelope. One order, poor in species.

[119]

Family 2. Perisporiales.

The ascocarps are surrounded by a complete envelope without any opening: the fruit-bodies are cleistocarpic; the spores are only liberated after the disintegration of the fruit-bodies. Paraphyses are wanting. The two first orders have in addition the means of reproduction by conidia.

Order 1. Erysiphaceæ, Mildews. The Fungi belonging to this order are epiphytic parasites, whose mycelium, somewhat resembling a cobweb, may be seen on the leaves and other green portions of plants (see Figs. 107, 108). The hyphæ ramify in all directions upon the surface of their host, and emit haustoria which penetrate the epidermal cells, and thus derive the necessary nutriment. The Mildew-Fungi thus belong to the obligate parasites, and during their growth dwarf and destroy the portions of their host on which they live. The reproduction takes place in the first instance by abstriction of conidio-chains from the end of special branches (Fig. 108 c, a hypha is seen in the act of detaching a conidium). The conidia may germinate immediately, and thus quickly reproduce their species. When present in large numbers they appear as a white meal covering the surface of the plant on which the fungus is found. Later on appear the dark brown, spheroid ascocarps (Fig. 108 a) which, although small, are generally just visible to the naked eye as black specks.

Fig. 107.—Erysiphe cichoracearum: a mycelium-threads; b sterile hypha (“pollinodium”); c fertile hypha (ascogone or archicarp); d and e young ascocarps.

A characteristic feature of the Mildew-Fungi is the thin, pseudo-parenchymatous[120] covering of the ascocarp, enclosing one (Podosphæra and Sphærotheca; compare Thelebolus among the Hemiasci) or a few asci (Fig. 108 c), which do not form any hymenium, but are irregularly placed. The cells of the ascocarp-envelope are often prolonged into hair-like appendages. The ascocarps are developed from the mycelium at places where two hyphæ cross each other (Fig. 107). At these places two short and erect hyphæ are produced side by side. The one from the lower hypha (Fig. 107 c) assumes an ellipsoidal shape, and is known as the archicarp or ascogone, while the other (“pollinodium”) arches over the ascogone. From the latter one ascus may be at once developed (Sphærotheca, etc.), or after its division several asci may be produced, each developed from one division. The sterile hypha (termed “pollinodium,” since it was formerly, but erroneously, supposed to fertilise the ascogone) produces a number of branches, and forms the pseudo-parenchymatous envelope of one cell in thickness, enclosing the asci.

Fig. 108.—Erysiphe communis. A small portion of a leaf with this Fungus growing upon it (considerably magnified). The hyphæ b and d do not belong to this Fungus, but are reproductive organs of a pyrenomycetous Fungus parasitic upon it (Cicinnobolus).

Many plants, both cultivated and wild, are attacked by various[121] species of Mildew. A common means of prevention against their attacks is to dust the diseased parts with sulphur.

Fig. 109.—Eurotium glaucum: α portion of mycelium lying horizontally; β vertically-placed conidiophore; the mycelium gives rise to another branch near α; the conidia are abstricted from short flask-shaped cells; b a ripe conidium; c, d germinating conidia; e spirally-twisted hypha, commencement of an ascocarp; f a stage later; g still later, the hypha at the base of the coil has given off branches which are applied to it; h, i sections of young ascocarps.

Order 2. Perisporiaceæ, Moulds and Mildews. A group of Fungi widely distributed and found in all situations. Usually they have a well-developed surface mycelium, and small, round, seldom conspicuous ascocarps, containing ovoid, pulley-like spores. They are partly saprophytic, partly parasitic, in the latter condition having a brown mycelium.

Fig. 110.—Eurotium glaucum: a longitudinal section of a half-ripe ascocarp, bounded externally by a well-defined layer of cells, enclosing asci in various stages of development; b a semi-ripe, c an almost ripe ascus; d and e spores seen from the edge and side; f germinating spore twenty-two hours after been sown in plum juice.

Eurotium glaucum (= E. herbariorum, Figs. 109, 110) and E. repens live on dead organic matter, preserved fruits, etc. The conidial forms of both species are known as “Moulds” (Fig. 109), and formerly were described under the name “Aspergillus glaucus.” The conidia for some time remain attached to each other in chains (Fig. 109 a); they are abstricted from sterigmata arranged radially on the spherical, swollen end of the conidiophore. The small yellow or brownish ascocarps are frequently found in herbaria, especially when the specimens have been insufficiently dried. Aspergillus fumigatus and others are pathogenic, causing mycosis in warm-blooded animals.

Fig. 111.—Penicillium crustaceum: a conidia (× 300); b germination of conidia; c small portion of mycelium, produced from a conidium at *, with five conidiophores; d young conidiophore (× 630), a flask-shaped cell is abstricting a conidium; e the same conidiophore after 9–10 hours.

Fig. 112.—Penicillium crustaceum: a two spirally-coiled hyphæ arise from the mycelium, from one of which (archicarp) the asci are produced; b a further step in the development of the ascocarp; the branching archicarp is surrounded by sterile hyphæ; c section of young ascocarp; the larger hyphæ in the centre are the ascogenous hyphæ; these are enclosed by a pseudo-parenchyma of sterile hyphæ (× 300); d series of ripe asci with spores; e four ascopores seen laterally; f germinating ascospores (× 800).

Penicillium crustaceum (P. glaucum, Figs. 111, 112) is an exceedingly common “Mould.” Its mycelium appears very frequently on any organic matter which is permitted to remain untouched, and soon covers it with a dense mass of blue-green[123] conidiophores. These branch at their summits and bear flask-shaped cells from which the conidia are abstricted. The ascocarps which, both in size and colour, resemble grains of sand, have only[124] been obtained in luxuriant cultivation with a limited supply of oxygen.

Order 3. Tuberaceæ, Truffles. The Fungi belonging to this order are entirely subterranean. The mycelium is filamentous, and partly parasitic upon the roots of plants, especially trees, in its neighbourhood; it is then known as Mycorhiza. The fruit-body is relatively large, in some cases about the size of a hen’s egg. Internally it is traversed by a number of winding passages (Fig. 113 a), the walls of which are coated with the asci. The asci (b) contain only a small number of spores, and these are set free by the putrefaction of the fruit-body. Conidia are unknown.

Fig. 113.—Tuber melanosporum: a fruit-body (nat. size), a portion having been removed to show the internal structure; b an ascus with ascospores.

[125]

Family 3. Pyrenomycetes.

In this family the hymenium is enclosed in small fruit-bodies, perithecia (Fig. 120 b), which appear to the naked eye as small dots. In shape they resemble a globe or a flask with a narrow mouth, through which the spores are ejected (peronocarpic ascocarps). Different kinds of reproduction—conidia, pycnidia (chiefly with microconidia), chlamydospores, and perithecia—are found in the same species. The various stages in the life-history of these Fungi are so dissimilar, that formally they were considered to be different genera. Ergot furnishes a very good example.

Fig. 114.—A small portion of an ovary attacked with Claviceps purpurea (Sphacelia).

Fig. 115.—An ovary with the conidial stage of Claviceps purpurea (Sphacelia).

This family may be subdivided into 3 sub-families.

Sub-Family 1. Hypocreales.

The perithecia are pale, fleshy, brightly coloured, and generally aggregated on a stroma. Conidia and chlamydospores occur very frequently. Only one order.

Order. Hypocreaceæ. In this order the majority are parasites upon Flowering-plants (Nectria, Polystigma, Epichloë, Claviceps); but some are parasites upon Fungi (Hypomyces, Melanospora), or upon insects (Cordyceps).

Fig. 116.—Claviceps purpurea. A Sclerotium with stromata (cl) (× by 2). B Stroma divided longitudinally to show the perithecia (cp). C A perithecium with the surrounding hyphæ (hy). D An ascus ruptured, with the eight filamentous ascospores emerging.

The most important member of this order is the Ergot (Claviceps purpurea, Figs. 114, 115, 116). This Fungus is found in the flowers of many species of Grasses, especially the Rye, attacking and destroying the ovaries. In the FIRST or CONIDIAL STAGE of the attack, the ovaries are found covered with a white, irregularly[126] folded mycelium (Fig. 114 m, Fig. 115), formed of numerous hyphæ woven together and penetrating the wall of the ovary. From these a number of hyphæ (Fig. 114 a) project into the air and abstrict from their apices the conidia (b) which serve as reproductive organs. The mycelium also secretes a sticky, stinking fluid (honey-dew) in which the conidia are embedded in great numbers. The honey-dew exudes from the bases of the glumes, and is greedily sought by flies, which thus carry the conidia to other ovaries. In this manner fresh ears are infected, which might escape were the conidia only distributed by the wind. This stage formerly was regarded as an independent Fungus, known as Sphacelia segetum (Fig. 115). On germination, the conidia produce either a new mycelium (Fig. 114 d, c), or new conidia. The SECOND or SCLEROTIUM STAGE is the one in which the Fungus passes the winter. The mycelium penetrates deeper and deeper into the attacked ovaries, their tissues are destroyed and replaced by the hyphæ, which gradually become more and more felted together.[127] A firm, pseudo-parenchymatous mass of hyphæ is thus formed at the base of the loosely-woven Sphacelia, which is in part transformed into the hard sclerotium, and the remainder thrown off. A dark, hard, poisonous body, longer than the natural grain, is thus formed; these bodies are known as Ergots, and were formerly considered to be a distinct species,—Sclerotium clavus (“Secale cornutum,” Ergot, Fig. 116 A, c). The THIRD STAGE, described as Claviceps purpurea, is developed in the following spring from the germinating sclerotium, which produces dark-red stromata with short stalks. In the stroma numerous perithecia with asci and ascospores are produced. The latter may infect young flowers of the cereals, in which the disease is then developed as before.

Fig. 117.—Nectria cinnabarina: a branch of Acer pseudoplatanus, with conidial-layers and perithecia (nat. size); b a conidial-layer (Tuberculoria vulgaris); c, a mass of perithecia. (b and c × 8.)

Fig. 118.—Cordyceps militaris. I Stromata with conidiophores (Isaria farinosa). II A larva, with stromata, bearing perithecia. III A spore.

Fig. 119.—Cordyceps robertii on the larva of Hepialus virescens: a stalk of stroma; b perithecia.

[129]

Sub-Family 2. Sphæriales.

To this sub-family belong the majority of the Pyrenomycetes. The perithecia are of a firm consistence (tough, leathery, woody or carbonaceous), and of a dark colour. Their covering is quite distinct from the stroma when this structure is present. The stromata are sometimes very large, and may be either cushion-like, crustaceous, upright and club-like, or branched bodies. In general, small, inconspicuous Fungi, living on dead vegetable matter, sometimes parasites. Free conidiophores and conidiocarps are known in many species, and in several, chlamydospore-like forms of reproduction. Orders 3–18 constitute the Sphæriaceæ of older systematists.

Fig. 120.—Strickeria obducens: a a portion of an Ash-branch with the bark partly thrown off; on the wood are numerous black perithecia (× 20); b longitudinal section through a perithecium; c a spore; d longitudinal section through a pycnidium whose ascospores are being ejected; e portion of the same, with hyphæ and spores.

[130]

Fig. 121.—Trichosphæria parasitica: a a twig of Abies alba, with epiphytic mycelium; b a leaf with mycelium and sporangia (magnified); c a sporangium (× 60); d an ascus with spores (× 550).

[131]

Order 18. Xylariaceæ. This order is the most highly developed of the Sphæriales. The stroma arises on the surface of the substratum, which is generally dead or decorticated wood; it is well-developed, crustaceous, hemispherical or upright. In the younger conditions it is covered with a layer of conidia, and later on it bears the perithecia, arranged in a layer immediately beneath its surface. The ascospores are of a dark colour. Often also there are free conidiophores.

Fig. 122.—Xylaria hypoxylon (nat. size) on a tree stump: a younger, b an older stroma, both of which, with the exception of the black lower portion, are covered with white conidia; n, spot where the perithecia are developed; c an old stroma with upper part fallen off; d, e large branched stromata; k conidia.

Sub-Family 3. Dothideales.

The perithecia are always embedded in a black stroma, and are not distinctly separated from it. The accessory forms of reproduction are: conidiophores, conidiocarps, and yeast-like conidia. The majority are parasites. One order.

[132]

Family 4. Hysteriales.

This family, like the following, has hemiangiocarpic ascocarps (apothecia). These are closed in the early stages, but when ripe open in a valvular manner by a longitudinal fissure; they are black, oblong, and often twisted. Some species are parasites, especially upon the Coniferæ.

Fig. 123.—Lophodermium (Hypoderma) nervisequium: a two leaves of Abies alba seen from above with pycnidia; b a leaf seen from the underside with apothecia; c an ascus with ascospores. (× 500.)

Fig. 124.—Three leaves of the Red-pine with Lophodermium macrosporum: a under side of the leaves with apothecia; b a leaf from upper side with pycnidia. (× about 2.)

Fig. 125.—Lophodermium pinastri: a leaves of Pinus sylvestris with apothecia (nat. size); b two paraphyses and an ascus with filamentous spores.

Family 5. Discomycetes.

The ascocarps (apothecia) are at first closed, and only open at the time of their ripening, not valvularly, but more or less[133] like a saucer or cup, so that the hymenium lies exposed on their upper surface. In the first three sub-families, and generally also in the fourth, the apothecia are formed inside the substratum. The apothecia are, in contrast to the Pyrenomycetes, light and brightly coloured, and their size varies very much, and may be several centimetres in diameter. Paraphyses are often present between the asci; they often contain colouring matter, and give to the disc its characteristic colour. The tissue on which the asci are borne is known as the hypothecium. The shape and colour of the spores is not so varied as in the Pyrenomycetes. The accessory forms of reproduction are conidia (sometimes of two forms), chlamydospores, and oidia. The family is divided into 5 sub-families.

Sub-Family 1. Phacidiales.

The apothecia are developed in the interior of the substratum, which they break through, and in general dehisce apically. The envelope is tough and black. Hypothecium inconspicuous; hymenium flat.

Sub-Family 2. Stictidales.

The apothecia when ripe break through the substratum which forms a border round them. Hymenium generally saucer-shaped.

Sub-Family 3. Tryblidiales.

The apothecia are embedded in the substratum in the early stages, and then are raised high above it. Hypothecium thick. Hymenium cup-shaped.

[134]

Sub-Family 4. Dermateales.

The apothecia in the early stages are embedded in the substratum and then break through it, or are from the first situated on the surface of the substratum. Hypothecium thick.

Fig. 126.—Botrytis cinerea: a slightly magnified; b more highly magnified; c germinating conidium.

Fig. 127.—Sclerotinia fuckeliania: a sclerotium with conidiophores; b with apothecia; c section through sclerotium and apothecium; d ascus with eight ascospores. (× 390.)

Sub-Family 5. Pezizales.

The apothecia are developed on the surface of the substratum and are waxy or fleshy; at the commencement closed, and covered with a saucer- or cup-shaped, seldom flat, hymenium. The hypothecium is generally well developed. This sub-family is the richest in[135] species of the Discomycetes and contains forms of very different habit. They grow upon dead wood, upon the ground, and upon dung. A few are parasites.

Order 1. Helotiaceæ. Apothecia with waxy envelope of colourless, or yellowish prosenchymatous cells.—Chlorosplenium æruginosum is found on decaying wood (particularly Oak and Birch), to which it gives a green colour. Sclerotinia has sclerotia which are developed upon the host-plant and from which, after a period of rest, the long, brown-stalked apothecia arise. S. ciborioides (S. trifoliorum, Fig. 128) is parasitic on Clover; S. sclerotiorum, on Daucus-roots, Phaseolus, etc.; S. baccarum, on the berries of Vaccinium myrtillus; “Botrytis cinerea” is a common parasite and is probably the conidial form of S. fuckeliania (Fig. 127).—Helotium herbarum lives on dry plant stems.—Dasyscypha willkommii (Fig. 129) produces Larch-canker on the bark of the Larch.

Fig. 128.—Sclerotinia ciborioides: a sclerotium with three apothecia slightly magnified; b ascus with eight ascospores; c germinating ascospore.

Fig. 129.—Dasyscypha willkommii: a portion of bark of Larix decidua with sessile, cup-shaped apothecia (nat. size); b two paraphyses on either side of an ascus with eight ascospores.

Order 3. Pezizaceæ. This order contains the largest and morphologically the highest forms of the Discomycetes. Apothecia fleshy, and in the later conditions generally saucer-shaped.

Family 6. Helvellales.

These Fungi have the appearance of clubs, bells, or mushrooms, consisting of an upright stalk bearing a large and fleshy head, on the exterior surface of which the hymenium is spread. The ascocarps are probably gymnocarpic from the beginning, and on this account these plants are placed in a separate family. The development of the ascocarps is unknown. The Morchella (Morell) grows on the ground; some species are edible. 1 order.

Fig. 130.—Morchella esculenta: a an entire specimen, about one half natural size; b longitudinal section through the head.

Appendix to the Ascomycetes:

Family 7. Ascolichenes (Lichen-forming Ascomycetes).

The Lichens were formerly classed among the Thallophyta as a group quite distinct from the Algæ and Fungi. Investigations during the last twenty-five years, however, have conclusively proved that the Lichens are Fungi which reproduce in the same manner as the Ascomycetes, or, more rarely, the Basidiomycetes, and have entered into a peculiar symbiotic relation with Algæ, especially the Cyanophyceæ and Protococcoideæ, with which they associate, and without which they would be unable to exist. The Fungus forms the largest portion of the Lichen, enclosing the Alga with which it may be said to be commensal. The Fungus especially produces reproductive bodies and absorbs the inorganic nourishment through the rhizoids, whilst the Alga supplies it with the organic materials. In consequence of this the Lichens, in contradistinction[137] to other Fungi, need light for the development of their nutritive organs, and are therefore, in any case internally, of a more or less greenish colour. The form and condition of the thallus is unusual among the Fungi, and they can grow upon rocks and in other places where no dead organic matter, such as would be required by other Fungi, is obtainable.

Fig. 131.—Transverse section through the thallus of Sticta fuliginosa (× 500): r-r rhizoid-strands, which arise from the under side; g-g gonidial layer; m medullary layer; o upper, u lower cortex.

Two cellular forms are therefore to be found in each Lichen:

1. The cells which belong to the Fungus. These are generally septate, branched hyphæ without any trace of chlorophyll. In the thallus of the majority of Lichens there may be found a medullary layer (Fig. 131 m) of loosely-woven hyphæ, between which there are large air chambers; and an external layer (cortex) (Fig. 131 o, u) formed of closely-woven hyphæ without any intercellular spaces. In some Lichens (Collemaceæ) the hyphæ wind about in the thallus, being equally distributed throughout, without forming any decided strata. These Lichens moreover become[138] gelatinous when exposed to moisture (Fig. 132), on account of the swelling of the walls of the Algæ. The hyphæ contain protoplasm with drops of oil, but never starch; their walls easily swell when exposed to damp after having been dried, and in some (e.g. Cetraria islandica) they become gelatinous when cooked. Certain strata of hyphæ become blue on treatment with iodine alone, from which it is inferred that the wall is allied, in its chemical nature, to starch.

2. The enclosed Algæ, termed “gonidia.” Some belonging to the Cyanophyceæ, Protococcoideæ, (especially Pleurococcus) and Chroococcaceæ, are spherical and are found isolated, or in irregular groups of cells (Fig. 131 g); some belonging to Nostoc (Fig. 132 g), Lyngbyaceæ, etc., are placed in cell-rows. Each Lichen, as a rule, has only one definite Algal-form for its gonidium.

The gonidia either lie together in a certain stratum between the cortex and the medullary layer (Fig. 131 g), or are scattered irregularly throughout the entire thallus (Fig. 132). The thallus is in the first instance termed “heteromerous,” in the second instance, “homoiomerous.” The Fungal-hyphæ embrace the gonidia and apply themselves closely to, or even penetrate them, and hence it has been difficult to decide whether the one cellular form does or does not develop from the other (Figs. 134, 135).

Fig. 132.—Collema microphyllum. Transverse section through the thallus; g Nostoc-chains; h hyphæ.

[139]

Fig. 133.—Ephebe pubescens. The apex of a branch of the thallus with two lateral branches (s): h its hyphæ; g the apical gonidium of the main branch.

Fig. 134.—Nostoc lichenoides, which is attached by a germinating thread (h) of Collema glaucescens.

Fig. 135.—A Germinating spore of Physcia parietina with Protococcus viridis. B Synalissa symphorea with Glæocapsa. C Cladonia furcata with Protococcus.

The thallus of the Lichen appears mainly under three forms:—

1. The Crustaceous, which adheres firmly to the substratum (bark, stone) throughout its entire surface, without being raised into any free patches or lobes. It has, in many instances, no definite outline, and hyphal-branches from it often penetrate[140] deeply into the substratum. It grows at the circumference and sometimes dies away in the centre (Figs. 138, 139, 140).

2. The Foliaceous. This also lies flat upon the substratum, but is not firmly attached to and has a definite outline. It grows at the margin, and raises itself a little by free outgrowths and lobes (Fig. 141). The rhizoid-strands spring out from its whitish under surface (Fig. 131, r).

Fig. 136.—Portion of a hymenium: d a thin stratum on which the asci (s) are situated.

Fig. 137.—Spores of, a Cladonia, Lecanora and Pertusaria; b Bæomyces; c Sphinctrina; d, e, f various species of Parmelia; g, h Verrucaria in its younger and older condition; i, k species of Leptogium.

3. The Fruticose, which is attached to its substratum at a small point from which it projects freely, either erect or pendulous. It is more or less tufted, in the form of a bush (Figs. 142, 143). These three thallus-forms gradually pass over by many intermediate forms into one another.

Fig. 138.—Lecanora subfusca: a the bark on which it is situated; l the thallus; s the ascocarp; s’ an ascocarp.

Fig. 139.—Graphis (two species).

Fig. 140.—Pertusaria communis.

The Lichens, like other Ascomycetes, have very variously[141] constructed ascospores (Fig. 137), which are enclosed in asci (Fig. 136), usually surrounded by paraphyses attached together. Furthermore they possess pycnidia (Fig. 141) containing numerous microconidia. These were formerly considered as organs of fructification, and were termed “spermatia,” and the pycnidia, “spermogonia.” Alfr. Möller proved, in 1887, that the microconidia are able to germinate and produce a mycelium with new conidia, just as in other Ascomycetes.

Vegetative Reproduction takes place by soredia, which to the naked eye appear as whitish powder on the surface of the thallus. They are small round bodies, formed by one or a group of gonidia, which are surrounded by a mass of felted hyphæ. After the rupture of the cortex they are set free, and readily carried by the wind to other places, where under favourable circumstances they establish a new thallus.

Fig. 141.—A A portion of the thallus of Parmelia parietina with ascocarps (a) and pycnidia (b). B A portion of the thallus of Cetraria islandica with pycnidia at the end of small lobes. C A lobe with pycnidia and ejected microconidia. (Magnified).

Geographical Distribution. The Lichens are the most hardy plants, and are the first to appear on hitherto bare rocks which they gradually disintegrate, and hence prepare the way for the growth of other plants. They are to be found from the Polar regions to the Equator; from the highest snow-free mountain-peaks down to the level of the sea; on the stems of trees; on rocks, soil, some even on inundated places; on stones in woodland streams, and on beaches; but they are never found upon rotten organic remains. Some grow gregariously in enormous masses, and form wide-stretching carpets, e.g. Reindeer Moss (Cladonia rangiferina), species of Cetraria and other fruticose Lichens.

Uses. On account of the cell-wall being composed of Lichenstarch[142] (Lichenin), the Iceland-Lichen and Manna-Lichen (Lecanora esculenta) are used as food; the latter grows on stones, in the deserts of Asia and North Africa, and is often torn loose in large masses and carried away by the wind. The Reindeer-Lichen is not only the principal food of the reindeer, but it is also used in the manufacture of Danish brandy. Cetraria islandica (Lichen islandicus) is OFFICINAL. Colouring materials (lacmus, orseille, persio) are made from several species, especially from Roccella tinctoria (from the rocky coasts of the Mediterranean). Parmelia saxatilis and particularly Lecanora tartarea are used for colouring purposes in the Northern countries.

About 2,000 species of Lichens have been described. If we disregard the Basidiolichenes, which will be considered on page 176, the remaining Lichens (Ascolichenes) may be divided into the two following orders according to the structure of the fruit-bodies:—

Order 1. Pyrenolichenes. The ascocarps (apothecia) are spherical or flask-shaped, as in the Pyrenomycetes, more rarely linear (Graphis).

Order 2. Discolichenes. These, as in the Discomycetes, have open apothecia, which, as a rule, are cupular, more rarely hemispherical (Cladonia).

Fig. 142.—Cladonia rangiferina: s ascocarp.

Fig. 143.—Usnea barbata: s ascocarp. (Slightly magnified.)

Fig. 144.—Cladonia pyxidata.

[144]

Sub-Class 2. Basidiomycetes.

This sub-class embraces the most highly developed Fungi, with large “fruit-bodies,” which in ordinary language we shortly term Funguses, Toadstools, or Mushrooms.

They have no sporangia, but reproduce only by means of basidiospores, conidia, chlamydospores and oidia. The chief characteristic of this sub-class is the basidium (Fig. 145), i.e. the conidiophore, which has a distinctive form, and bears a definite number (generally 4) of characteristically shaped conidia (basidiospores, Fig. 145 c, d, e).

Fig. 145.—Development of spores in Corticium.

The summit of each basidium is produced generally into four conical points (sterigmata, Fig. 145 b), from each of which a basidiospore is abstricted. The basidia may be classified into three principal groups, each of which accompanies a distinctive conidiophore: 1, the long, filamentous, transversely divided basidia, with lateral sterigmata and spores, found in the Uredinaceæ (Figs. 146 D, 153), Auriculariaceæ (Fig. 160 B), and Pilacraceæ; 2, the spherical, longitudinally divided basidia of the Tremellaceæ (Figs. 160 C d; 161 iii. iv.); and 3, the ovoid, or cylindrical, undivided basidia of the Autobasidiomycetes (Figs. 145, 163, etc.); the two last have apical sterigmata and spores.

In addition to the basidia, simple conidiophores are also found. In the Protobasidiomycetes, the simple conidia are very generally found as accessory methods of reproduction in conjunction with the basidiospores; but less frequently in the Autobasidiomycetes, e.g. among the Dacryomycetes, Tomentellaceæ, Heterobasidion annosum.

Finally, well-defined chlamydospores, formed in various ways, appear in the Basidiomycetes as supplementary reproductive bodies (compare p. 90). Among the Protobasidiomycetes, chlamydospores are at present only found among the Uredinaceæ, but in various forms; in the majority of families of the Autobasidiomycetes oidia frequently occur (Fig. 162), but genuine chlamydospores seldom.

In the same species several of the known forms of reproduction may be distinguished.

The mycelium is generally composed of white, branched strands, consisting of numerous felted hyphæ; in some, sclerotia are found.—The great majority are saprophytes; some (particularly all the Uredinaceæ), are parasites.

Divisions of the Basidiomycetes.

• Series 1. Protobasidiomycetes: partly gymnocarpic, partly angiocarpic.
•   „ 2. Autobasidiomycetes.
• Family 1. Dacryomycetes: gymnocarpic.
•   „ 2. Hymenomycetes: partly gymnocarpic, partly hemiangiocarpic.
•   „ 3. Phalloideæ: hemiangiocarpic.
•   „ 4. Gasteromycetes: angiocarpic.
• Appended. Basidiolichenes: Lichen-forming basidiomycetes.

Series I. Protobasidiomycetes.

To this series belong the lowest of the Basidiomycetes. The basidia appear in two principal forms (1 and 2 on page 144) and are divided into four cells, either transversely or longitudinally, each division forming a sterigma which abstricts a basidiospore. The first three orders, Uredinaceæ, Auriculariaceæ, and Tremellaceæ[146] have gymnocarpic fruit-bodies, while those of the Pilacraceæ, on the contrary, are angiocarpic.

Order 1. Uredinaceæ (Rusts). All the Rust-Fungi are parasites, their mycelium living in the interior of the stems and leaves of their hosts, causing red, brown, or black spots—hence their name—and malformations, sometimes of considerable size.

The Rust-Fungi are gymnocarpic and destitute of a hymenium; for these reasons they are regarded as the simplest order of the Basidiomycetes. They are entirely parasitic, and their filamentous, branched mycelium ramifies in the intercellular spaces of its host, and often protrudes haustoria into the cells. The mycelium is perennial should it enter a woody tissue; it may also hibernate in the rhizomes of perennial herbs and permeate the shoots springing from them, but in the majority of the Rust-Fungi the mycelium has a very limited growth. The chief means of reproduction of the Rust-Fungi are the chlamydospores, which in the more highly developed species occur in three forms, namely, the teleuto-, æcidio-, and uredo-spores. The spores, in the host, are formed immediately beneath its epidermis, which is ruptured on the ripening of the spores, with the production of “rust,” brown, red, or black spots. Those chlamydospores which produce basidia are termed teleutospores. The spore on germination produces a transversely divided basidium, “promycelium,” on which basidiospores, “sporidia,” generally four in number, are produced on lateral sterigmata. This basidio-fructification is gymnocarpic; the basidia neither form a hymenium nor a fruit-body (only Cronartium and Gymnosporangium have a slight indication of a basidio-fructification).

Many Rust-Fungi, in addition to basidiospores, have small, unicellular conidia, “spermatia,” which are borne in conidiocarps, “spermogonia.”

The TELEUTOSPORES (Winter-spores) may be either unicellular or multicellular; in the majority of cases they are enclosed in a hard outer cell-wall, the exospore, which in some cases is very strongly developed; they have also a long or short stalk, the remains of the spore-bearing hypha. Each cell of the teleutospore has one germ-pore (a thin portion of the wall, for the protrusion of the germ-tube; in Phragmidium and Gymnosporangium there are, however, several germ-pores). The colour of the teleutospores is generally much darker than that of the uredospores, and it is by these that the majority of the Rust-Fungi hibernate.

[147]

The ÆCIDOSPORES (Spring-spores) are produced in chains which are generally enclosed in an envelope of hyphæ, the peridium; the peridium enclosing the spores being termed the æcidium. The æcidiospores are unicellular, and generally of an orange colour; they are often separated by intermediate cells which wither and so assist in the distribution of the spores. The exospore is made up of minute, radially arranged rods. Generally germination proceeds immediately, the æcidiospore producing a germ-tube, which developes into a mycelium bearing either uredo- or teleutospores.

The UREDOSPORES (Summer-spores) are unicellular and arise singly, seldom in chains (Coleosporium). Their colourless, warty exospore bears, in the equatorial plane, 2–8 germ-pores. In the majority, germination proceeds immediately, and a mycelium is produced which at first gives rise to uredospores and afterwards to teleutospores.

The spermogonia are spherical or pear-shaped conidiocarps, generally embedded in the substratum, and are produced before the æcidia, before or simultaneously with the uredospores, or before the teleutospores. The conidia, as far as observations go, do not generally germinate under ordinary conditions.

Among the Rust-Fungi some species are found which only form basidiospores and teleutospores (Puccinia malvacearum,[148] Chrysomyxa abietis). Other species have in addition uredospores; others spermogonia and uredospores; others spermogonia and æcidia; others spermogonia, uredospores and æcidia. Those species in which all the methods of reproduction are not developed must not be considered as incomplete forms.

As a rule the mycelium, which is produced from the basidiospores, developes æcidia; in the species, however, without æcidia, it developes the uredo-form, and when the uredospores are also absent, the teleutospore-form. It has been established in some species of Puccinia and Uromyces that the formation of æcidia can be suppressed, and it is not a necessary part of the cycle of development of the species.

Among the Rust-Fungi, with several forms of reproduction, there are about sixty whose development can only be completed by an alternation of hosts, that is, on one host only uredo-and teleutospores are produced, while the further development of the germinating basidiospores, and the formation of the æcidia and spermogonia from its mycelium, can only take place on a second quite distinct and definite host (heterœcious or metoxenous Fungi). Those Fungi which have all their forms of reproduction on the same host are termed autœcious or autoxenous. It is not, however, always necessary that the heterœcious Rust-Fungi should regularly change their hosts; for example, Puccinia graminis can hibernate in the uredo-form on the wild Grasses, and in the spring can distribute itself again in the same form.

Fig. 146.—Puccinia graminis.

As an example of one of the most highly developed species, Puccinia graminis, the “Rust of Wheat,” holds a prominent position. Its uredospores and teleutospores are produced (Fig. 146) on Grasses (on cereals, especially Wheat, Rye, Oats, and many wild Grasses), while the æcidia and spermogonia are confined to[149] the Berberidaceæ. The teleutospores, developed on the Grasses, hibernate on the dried portions of their host, and in the succeeding year each of the two cells of the teleutospore may develop a basidium with four basidiospores (Fig. 146 D, c). The basidiospores are distributed by the wind, germinate quickly, and only proceed to further development on Berberis or Mahonia. The germ-tube bores through the epidermis of the Barberry-leaf, and forms a mycelium in its interior, its presence being indicated by reddish-yellow spots on the leaf. After 6–10 days the flask-shaped spermogonia appear (Fig. 147 B; C, a; conidia in Fig. 147 D) and a few days later the cup-shaped æcidia (Fig. 147 A; C, c, d, e). The former are generally on the upper, and the latter on the under side of the leaf. The orange-coloured æcidiospores scatter like dust, and germinate only on Grasses; the germination takes place in about two days when placed on any green part of a Grass. The germ-tube enters the Grass-leaf through a stoma; a mycelium is developed in the leaf, giving rise to a small, oval, rust-coloured spot (Fig. 146 A); in about 6–9 days the epidermis is ruptured over the red spot, and numerous reddish-yellow uredospores, formed on the mycelium, are set free. The uredospores (Fig. 146 B) are scattered by the wind, and can[150] germinate should they fall on the green portions of other Grasses: they then emit 2–4 germ-tubes through the equatorially-placed germ-pores. The germ-tubes enter a leaf through a stoma, a new mycelium is then developed, and in about eight days a fresh production of uredospores takes place, which germinate as before. The uredospore-mycelium very soon produces, in addition, the brown teleutospores, which give a brown colour to the rust-coloured spots, the familiar uredospores on the cereals being quite suppressed towards the close of the summer (Fig. 146 C, D). The “Rust of Wheat” hibernates on some wild Grasses in the uredospore-form.

Fig. 147.—Æcidium berberidis. A Portion of lower surface of leaf of Barberry, with cluster-cups (æcidia). B A small portion of leaf, with spermogonia, from above. C Transverse section of leaf on the upper side, in the palisade parenchyma are three spermogonia (a b); on the lower side an unripe æcidium (c d) and two ripe æcidia (d, e, f); f chain of æcidiospores. D Hyphæ, forming conidia.

Fig. 148.—Gymnosporangium sabinæ. A small portion of the epidermis of a Pear-leaf (a) pierced at b by the germinating basidiospore (c).

Fig. 149.—Uromyces genisteæ; a uredospore; b teleutospore.

Fig. 150.—Phragmidium gracile: a an uredospore; b and c two paraphyses; d a young teleutospore; e a teleutospore with a basidium and two basidiospores (s); f two series of æcidiospores (Ph. rosæ).

Fig. 151.—Melampsora padi: a and b uredospores; c-f teleutospores, seen from different sides.

Fig. 152.—Pear-leaf, seen from the under side, with “Rœstelia cancellata”: in different ages (a youngest, d oldest).

Fig. 153.—Melampsora betulina: a uredospores; b three contiguous teleutospores, one of which has developed a basidium with three basidiospores. (× 400.)

Fig. 154.—Gymnosporanginum juniperinum: a a small leaf with three clusters of æcidia (nat. size); b three conidia; c two æcidiospores on one of which are seen the germ-pores; d a portion of the wall of an æcidium; e, f two teleutospores.

Fig. 155.—Coleosporium senecionis: a Pine-leaves with æcidia (Peridermium wolffii) nat. size; b an æcidiospore; c a germinating æcidiospore; d a chain of uredospores; e a chain of teleutospores of which the terminal one has germinated and produced a basidiospore (s).

[154]

Fig. 156.—Chrysomyxa abietis: a leaf of the Fir, with 5 clusters of basidiospores (× 4); b branched rows of teleutospores springing from the mycelium (m).

Fig. 157.—Cronartium ribicola: a mass of uredospores (× 50); b an uredospore; c a column of teleutospores (× 60); d a small portion of the same more highly magnified, with a basidium and two basidiospores (s).

Fig. 158.—Æcidium strobilinum: a scale of cone of Picea excelsa, with numerous æcidia; b æcidiospores arranged in a series; c a cell of the peridium.

Order 2. Auriculariaceæ. The long, transversely divided basidia bear laterally 4 long sterigmata with basidiospores (Fig. 160 B) and are united to form an hymenium on the surface of the fruit-body. Parasites or saprophytes.

[156]

Order 3. Tremellaceæ. The round, pear-shaped, longitudinally divided basidia bear 4 elongated sterigmata, situated apically, and 4 basidiospores (Fig. 160 C, D), and are united into the hymenium on the surface of the fruit-body. The fruit-bodies are frequently gelatinous and quivering; similar fruit-bodies are also found in the Dacryomycetaceæ and Hydnaceæ. Simple conidiophores, which appear not infrequently in the basidiocarps, before the basidia, are known in many species. Saprophytes.

Fig. 159.—Peridermium strobi: æcidia of Cronartium ribicola (nat. size).

Fig. 160.—B Auricularia sambucina: a-d basidia in various stages of development; e a sterigma bearing a spore.—C Tremella lutescens: a-d basidia seen from various sides (b from above) and in various stages of development; e sterigma with basidiospore (× 400). D Exidia glandulosa: a-c various stages in the development of a basidium; d sterigma with basidiospore (× 350).

Order 4. Pilacraceæ. The transversely divided basidia have no sterigmata, but sessile basidiospores, and fill up the cavity of a closed (angiocarpic) fruit-body as a gleba without a regular arrangement (hymenium wanting).

Fig. 161.—Tremella lutescens: I and II fruit-bodies (nat. size); III vertical section through a fruit-body; b basidia; c conidia; IV-VI basidia; VII basidiospore with a second spore; VIII a basidiospore with yeast-like budding (cultivated); IX a conidiophore. (III-IX about 400.)

Series 2. Autobasidiomycetes.

This second and larger part of the Basidiomycetes is characterised by its more highly differentiated, undivided, club-shaped, or cylindrical basidia, which generally bear 4 (seldom 2, 6, 8) apically-placed sterigmata and basidiospores (Fig. 145). The fruit-bodies are partly gymnocarpic (in the first 3 orders and in some Agaricaceæ), partly hemiangiocarpic (in orders 3–6 of the Hymenomycetes[158] and in the Phalloideæ, the fruit-bodies in these orders are in the young conditions more or less angiocarpic, but later on generally open below and bear the hymenium on the under surface of the fruit-body), partly also angiocarpic (in the Gasteromycetes).

Fig. 162.—Dacryomyces deliquescens: I fruit-body (nat. size); II vertical section through the hymenium; III germinating basidiospore; IV a portion of mycelium with conidia; V a germinating conidium; VI and VII chains of oidia more or less strongly magnified; VIII basidiospore of D. longisporus; IX germinating basidiospore of D. ovisporus; X and XI Calocera viscosa; X fruit-body (nat. size); XI basidia with basidiospores (highly magnified); XII Dacryomitra glossoides (nat. size).

[159]

Family 1. Dacryomycetes.

The long, club-shaped basidia bear two tapering sterigmata, which develope remarkably large basidiospores (Fig. 162 II, XI) and form gymnocarpic fruit-bodies with hymenium. 1 order:

Order 1. Dacryomycetaceæ. This order comprises 4 genera of which the first two develope the hymenium on the whole surface of the fruit-body, but the two last only on its apex.

Family 2. Hymenomycetes.

This family is very rich in species (more than 8000 have been described), and to it belong all the “Mushrooms” and “Toadstools.” The fruit-bodies present very various forms; they are generally fleshy, very perishable, seldom leathery or corky, in the last case often perennial. The basidia are more or less cylindrical and bear generally 4 (seldom 2, 6 or 8) sterigmata and basidiospores. The hymenium in the fully-formed fruit-bodies lies free on the surface: in orders 1 and 2 and a portion of order 6 it is from the commencement exposed, fruit-bodies gymnocarpic; orders 3–6 have hemiangiocarpic fruit-bodies (p. 157). In the first order the basidia (or the hymenium) are developed immediately from the mycelium (Fig. 163); the fruit-bodies of orders 2 and 3 present a higher grade of development, and have between the mycelium and hymenium a special hyphal-tissue, a stroma, which is crustaceous, club-like, or coralloid, etc., and in general bears the hymenium on the largest part of the free, smooth surface. In the forms most highly developed (orders 4–6) a new tissue—the hymenophore—is introduced between the stroma and hymenium, which appears on the under side of the fruit-body in the form of warts, projections, tubes, folds or lamellæ (Figs. 166, 167, 174 bc). Paraphyses are frequently found in the hymenium, among the basidia. In the Hymenomycetes few examples of conidia can be recognised at first. More frequently chlamydospores are found, particularly oidia. The mycelium is richly branched, generally colourless, often perennial; it lives in humus or decaying wood, and is seldom parasitic.[160] The hyphæ generally have clamp-connections and unite, sometimes, to form a rhizomorpha (Fig. 177) or sclerotia with coloured, pseudo-parenchymatous covering.

Fig. 163.—Exobasidium vaccinii. I Hypertrophied stem of Vaccinium vitis idæa; II leaf with gall-like swelling; III section of II; IV transverse section: m mycelium between the parenchymatous cells; p hypodermal cells; e epidermis with basidia in various stages of development; V epidermis with germinating spores; VI and VII spores germinating in water (IV-VII × 620).

[161]

Order 1. Tomentellaceæ. To this order belong the simplest of the Hymenomycetes. The basidia (Fig. 145) arise free and irregularly from the mycelium; a hymenium is entirely absent or very slightly formed (in Corticium it attains its highest development); fruit-bodies are also wanting.—In general they form flaky, membranous or leathery coverings on bark and wood. Some are parasites.

Order 2. Clavariaceæ. The hymenium is situated on a stroma, and either completely covers the smooth surface of the more or less fleshy gymnocarpic fruit-body, or is confined to a tolerably well defined upper portion of it (Typhula). Paraphyses absent. The vertical, white, yellow, or red fruit-bodies are roundish or club-like, undivided or richly branched (Fig. 125). Generally on the ground in woods, seldom on tree-stems, etc.

Fig. 164.—Clavaria coralloides (nat. size).

[162]

Order 3. Thelephoraceæ. The hymenium is placed on a stroma and covers the smooth surface of the leathery hemiangiocarpic fruit-body, generally on its under side. The edge of the stroma, which bounds the hymenium, is sometimes especially developed (Stereum). Saprophytes.

Fig. 165.—Thelephora laciniata (nat. size).

Order 4. Hydnaceæ. The fruit-body is most frequently fleshy, and varies considerably in shape, the simplest forms being resupinate,[14] the higher ones umbrella-like. The hymenophore is found on the free or downward-turned surface, and always takes the form of soft emergences hanging vertically downwards. The emergencies may be thorn-, awl-, or wart-like. The species are found growing on the soil and on dead wood.

Fig. 166.—Hydnum auriscalpium, upon a Fir-cone, in different stages of development.

Order 5. Polyporaceæ (Pore-Fungi). An order very rich in species (about 2000 species are described). The fruit-body is of very different forms—resupinate, projecting like a bracket, hoof-like, or umbrella-shaped. In some it is fleshy and edible, in others leathery or corky, persisting for several years. The hymenophore is situated on the under side of the fruit-body, and consists of wide or narrow tubes or pores, whose inner surface is clothed with the hymenium (Fig. 167). In some fruit-bodies large cavities are to be found, which have arisen as interstices between the labyrinthine curved and reticulate folds. Chlamydospores are known in some species. Conidia occur very rarely. Many species work considerable damage: some as parasites on trees, others by destroying timber.

Fig. 167.—Polyporus igniarius. Section through the under side of the Fungus: h-h is hyphal-tissue between the tubes, formed by irregularly felted hyphæ, many of which are seen cut across; s is the hymenium which covers the walls of the tubes, and from which the basidia with the spores protrude.

Fig. 168.—Section of stem of a Beech attacked by P. fomentarius: a non-attacked parts of the stem; b the furrows where the mycelium has reached the bark, and where the thick mycelium-strands reach the exterior (⅙th of the nat. size).

Fig. 169.—Base of a Fir-tree, with a number of fruit-bodies of Heterobasidion annosum just beneath the surface of the soil, indicated by the dotted line (¼th nat. size).

Fig. 170.—A fully developed fruit-body of Polyporus pini (Trametes pini), lateral view (nat. size).

Fig. 171.—Boletus edulis (about ¼th): b longitudinal section of a portion of the pileus.

Order 6. Agaricaceæ (Mushrooms, Toadstools). The hymenophore consists of knife-like plates (lamellæ, gills), which are situated on the under side of the umbrella-like pileus of the fruit-body,[167] and radiate from the central stalk. Those which are first formed extend from the edge of the pileus to the stalk; those formed later reach only a longer or shorter portion of this distance, according to their age. In structure the lamellæ (Fig. 174) consist of a central mass of hyphæ, the trama, continuous with the hyphæ of the pileus; these terminate in a layer of shorter cells, the subhymenial layer, immediately beneath the hymenium which is composed of basidia and paraphyses. In a few species, but not in the majority, the lamellæ are branched, and in some they are decurrent. A few have the stalk placed excentrically, or it may be entirely absent.

Fig. 172.—Development of Psalliota campestris: a, b, c, d show the various stages of the development of the fruit-bodies and the mycelium (m) (nat. size); e the fruit-body in a somewhat later stage, slightly magnified; f longitudinal section of e; n first formation of the hymenium; g longitudinal section of a more advanced fruit-body (nat. size); n the hymenium; o velum partiale (see Fig. 133.)

In the early stages of its development the fruit-body is more or less enclosed in a hyphal tissue—the “veil” (velum universale, or volva). The veil at first completely encloses the young fruit-body, but is afterwards ruptured as the latter grows, part remaining at the base of the stalk as the “sheath” (annulus inferus), and part on the pileus as scales or warts. In the “Fly Mushroom” (Amanita muscaria) the remains of the veil are especially conspicuous[168] as white patches on the bright red ground of the upper surface of the pileus, and as a sheath at the base of the stalk (Fig. 178 v.). Another veil—the velum partiale—a hyphal tissue (Figs. 178 a; 173) stretches from the edge of the pileus to the stalk, and encloses the lamellæ. This veil is ruptured as the pileus expands, a portion attached to the stalk remaining as the “upper ring” (annulus superus) (Figs. 173, 178 a), or a part attached to the pileus hanging down as a fringe round its edge.—Some genera have no veil, the under side of the pileus being exposed from the first (gymnocarpic Agaricaceæ). Those which have a veil (hemiangiocarpic A.) afford a transition to the angiocarpic Gasteromycetes.

Fig. 173.—The cultivated Mushroom (Psalliota campestris).

The mycelium mostly grows in soils rich in humus or dung, on decaying trees and similar objects. Many species, e.g. Tricholoma personatum and Marasmius oreades, form the so-called “fairy rings.” The fruit-bodies in these species are confined to a larger or smaller surface on which they are very regularly arranged in a ring. The reason for this is found in the radial growth of the mycelium, so that the oldest portion, or the starting point, is found at the centre of the ring, and the younger ones, on which the fruit-bodies are formed, at the circumference. The older hyphæ gradually die, and at the same time, the radial growth continuing, the ring of fruit-bodies becomes larger and larger. The “fairy-rings” are marked[169] not only by the fruit-bodies, but also by the more vigorous growth and darker colour of the grass upon these spots.

Some species are parasites. An example is presented by Armillaria mellea, a remarkable and very destructive Fungus in woods and forests (Figs. 176, 177). In addition to the filamentous, white mycelium, it has also black, or black-brown, horny, root-like mycelium-strands (rhizomorpha) which were formerly considered to belong to a special genus of Fungi described under the name “Rhizomorpha.” The mycelium lives parasitically on the Conifers and other trees, forcing its hyphæ into the bark and between the bark and wood, and thence penetrating into the wood so that the tree is very severely attacked. It may also live saprophytically, and clusters of fruit-bodies are often found on old stumps and stems, on old timber, and in the rich soil of woods. The rhizomorpha, living underground, can extend for considerable distances and infect the roots of neighbouring trees, and spreads in this way the diseases known as “Harzsticken” and “Bark-Canker,” which are very destructive to young trees.

Fig. 174.—Psalliota campestris. A Tangential section of pileus showing lamellæ (l). B Portion of gill more highly magnified; t trama; hy hymenium with basidia and basidiospores; sh, subhymenial layer. C A portion of the same more highly magnified; s′ s′′ s′′′ s′′′′ various stages in the development of basidiospores; q paraphyses.

The chief characteristics by which the numerous genera are separated are the presence or the absence of the two kinds of veils, the nature of the fruit-body, the form, branching of the lamellæ, and their position and relation with respect to the stem, the shape of the[170] pileus, the colour of the spores, etc., etc. A knowledge of the colour may be obtained by placing the pileus with the lamellæ turned downwards on a piece of white or coloured paper, so that the spores, as they fall off, are collected on the paper, and the arrangement of the lamellæ can then be clearly seen.

Fig. 175.—Cantharellus cibarius (reduced).

Fig. 176.—Armillaria mellea. (½ nat. size): a root of a Fir; b rhizomorpha-strands; c-f fruit-bodies in four different stages of development.

Fig. 177.—The mycelium of Armillaria mellea (“Rhizomorpha”) (nat. size).

[171]

About 4,600 species belonging to this order have been described.

Fig. 178.—Fly Mushroom (Amanita muscaria).

Family 3. Phalloideæ.

The fruit-bodies before they are ripe are spherical or ovoid, and enclosed by a fleshy covering, the peridium, which is perforated at maturity and remains as a sheath (Fig. 179); the fruit-bodies are hemiangiocarpic.

Order 1. Phallaceæ (Stink-horns). The peridium has a complicated structure and is composed of three layers, the intermediate one being thick and gelatinous. The gleba (the tissue which bears the hymenium) is situated upon a peculiar receptacle which expands into a porous stalk and by its sudden distension, rupturing the peridium, elevates the gleba and hymenium above the peridium, which remains as a sheath. The gleba becomes gelatinous and dissolves away as drops. To this order belong many peculiar and often brightly coloured forms, which are natives of the Southern Hemisphere.

Fig. 179.—Phallus impudicus (Stink-horn), somewhat diminished. Fruit-bodies in all stages of development (b, c, d and k-m) are seen arising from a root-like mycelium (a); d longitudinal sections through a fruit-body before the covering has ruptured.

Family 4. Gasteromycetes.

The fruit-body is angiocarpic, fleshy at first, and later generally more or less hard and continues closed after the spores are ripe. The tissue lying immediately inside the peridium is termed the gleba; it is porous, containing a larger or smaller number of chambers lined with the hymenium, which is either a continuous[174] layer of basidia or else it fills up the entire cavity. The basidia as a rule bear four spores, sometimes eight (Geaster), or two (Hymenogaster). The tissue of the walls (trama) consists often (Lycoperdaceæ) of two kinds of hyphæ, some thin and rich in protoplasm, divided by transverse septa and bearing the basidia; others thicker and thick-walled which do not dissolve like the former on the ripening of the spores, but continue to grow and form a woolly, elastic mass, the capillitium, which may be regarded as highly developed paraphyses. The peridium may be either single or double, and presents many variations in its structure and dehiscence. The mycelium is generally a number of string-like strands, living in soils rich in humus.

Order 2. Lycoperdaceæ. The fruit-body has a double peridium; the external one at length breaks into fragments (Lycoperdon, Bovista), or it has a compound structure of several layers (Geaster) and detaches itself as a continuous envelope from the inner layer, which is membranous and opens at its apex. The interior of the fruit-body consists either solely of the fertile gleba (Bovista, Geaster), or, in addition, of a sterile tissue at the base (Lycoperdon). A capillitium is also present.

Fig. 180.—Lycoperdon gemmatum (½ nat. size).

Fig. 181.—I Hymenogaster citrinus (nat. size); II longitudinal section through H. tener (× 5); III portion of a section of H. calosporus; g a chamber; h hymenium; sp. spores; t trama (× 178); IV Rhizopogon luteolus (nat. size); V Scleroderma vulgare, VI section of V; VII basidia with spores belonging to the same Fungus.

Order 3. Sclerodermataceæ. Capillitium wanting. The peridium is simple and thick, gleba with round, closed chambers, which are filled with basidia.

[176]

Order 4. Nidulariaceæ (Nest-Fungi). Small Fungi of which the fruit-body at first is spherical or cylindrical but upon maturity it becomes cupular or vase-like, and contains several lenticular “peridiola” lying like eggs in a nest. The peridiola are the chambers which contain the hymenium, covered by a thin layer of the gleba, all the remaining portion of the gleba becoming dissolved. On decaying wood.

Order 5. Hymenogastraceæ. Fruit-bodies tubercular, globose and subterranean, resembling very closely the Truffles, from which they can only be distinguished with certainty by microscopic means. The peridium is simple, capillitium wanting, and the gleba encloses a system of labyrinthine passages covered with a continuous hymenium. The fruit-bodies persist for some time, and form a fleshy mass, the spores being only set free by the decay of the fruit-body, or when it is eaten by animals. The majority are South European. Hymenogaster, Melanogaster, Rhizopogon (Fig. 181 I-IV).

Appendix to the Basidiomycetes:

Basidiolichenes (Lichen-forming Basidiomycetes).

Several Fungi belonging to the Basidiomycetes have a symbiotic relationship with Algæ exactly similar to that enjoyed by certain Ascomycetes, and these are therefore included under the term Lichens (p. 136). They are chiefly tropical.

Order 1. Hymenolichenes. To this order belong some gymnocarpic forms: Cora, Dictyonema, Laudatea.[15]

Order 2. Gasterolichenes. To this belong some angiocarpic forms: Emericella, Trichocoma.

Appendix to the Fungi.

Fungi imperfecti (Incompletely known Fungi).

1. The Saccharomyces-forms are Fungi which are only known in their yeast-conidial form. They are conidia of higher[177] Fungi which can multiply to an unlimited extent by budding in nutritive solutions, and in this way maintain their definite size and shape. The budding takes place only at the ends of the conidia. The wall of the conidium forms at one or at both ends a small wart-like outgrowth, which gradually becomes larger, and is finally separated from its mother-cell as an independent cell, surrounded by a closed cell-wall (Fig. 182 a, b).

Fig. 182.—Beer-yeast (Saccharomyces cerevisiæ): a-b (× 400); c-f (× 750); c a cell in the process of forming spores; d a cell with four ripe spores; e the spores liberated by the dissolution of the cell-wall; f three germinating spores; g mycelium-like cell-chains. (× 1000: after Em. Chr. Hansen.)

Under very favourable conditions multiplication occurs so rapidly that the daughter-cells themselves commence to form buds, before they have separated from their mother-cell, with the result that pearl-like chains of cells are produced. When the yeast-cells have only limited nutriment, with an abundant supply[178] of air, at a suitable temperature, an endogenous formation of spores takes place. The protoplasm of the cells divides into 1–4 (rarely a greater number) masses (Fig. 182 c, d, e) which surround themselves with a thick cell-wall, and in this state can withstand adverse conditions and periods of dryness lasting for several months.

The sporangia are not asci since they have no definite form, and a definite number, form and size of spores is not found. The spores in the different species and kinds occupy varying periods for their development, although exposed to the same temperature, a fact of importance in determining one from another. On germination the wall of the mother-cell is destroyed, and each spore gives rise to a new cell, multiplication taking place by budding (Fig. 182 f). The majority of Yeast-Fungi are able to produce alcoholic fermentation in saccharine fluids.

The most important of these Fungi is the Beer-yeast (Saccharomyces cerevisiæ) with ovate, ellipsoidal or spherical cells (Fig. 182). It is a plant which has been cultivated from time immemorial, on account of its property of producing alcoholic fermentation in sugar-containing extracts (wort), derived from germinating barley (malt). Carbonic acid is also set free during this process. The “surface-yeast” (Fig. 182 a), which produces ordinary beer when the brewing takes place at higher temperatures, has cell-chains; “sedimentary yeast” (Fig. 182 b), used in the brewing of Bavarian beer, has spherical cells, solitary, or united in pairs. Both these and the following Yeast-Fungi include, according to Hansen, several species and kinds.

Fig. 183.—Saccharomyces mycoderma.

The “Ferment of Wine” (Saccharomyces ellipsoideus) produces wine in the juice of grapes. Uncultivated yeast-cells are always present on grapes; an addition of this species to the “must” is not necessary to secure fermentation. A large number of other “uncultivated” yeast-cells appear in breweries mixed with the cultivated ones, and cause different tastes to the beer (S. pastorianus, etc.). S. ludwigii, found, for instance, on the slimy[179] discharge from Oaks, produces abundant cell-chains on cultivation. S. apiculatus is very frequently met with on all kinds of sweet fruits, it has orange-like cells. S. mycoderma has cylindrical cells, often united together in chains (Fig. 183): it forms a whitish-gray mass (“fleur de vin”) on wine, beer, fruit-juice, etc., standing in bottles uncorked or not entirely filled. It is thought that this Fungus causes decomposition and oxydises the fluid in which it is found, but it cannot produce alcoholic fermentation in saccharine liquids, and it does not form endospores; hence it is uncertain whether it is true Saccharomyces.

Fig. 184.—Oidium lactis: a branched hypha commonly met with; b a hypha lying in milk and producing aerial hyphæ which give rise to oidia; c a branch giving rise to oidia, the oldest (outermost) oidia are becoming detached from one another; d a chain of divided cells; e germinating oidia in different stages (slightly more magnified than the other figures).

The “Dry-yeast” used in baking white bread is “surface-yeast.” In leaven, a kneaded mixture of meal, barm and water, which is used for the manufacture of black bread, Saccharomyces minor is present, and a species allied to this produces alcoholic fermentation in dough with the evolution of carbonic acid, which causes the dough to “rise.”

2. Oidium-forms. Of many Fungi only the Oidium-forms are known, which multiply in endless series without employing any higher form of reproduction. Oidium lactis (Fig. 184) is an imperfectly developed form which frequently appears on sour[180] milk and cheese. It can produce a feeble alcoholic fermentation in saccharine liquids. Thrush or aphthæ (O. albicans) appears as white spots in the mouths of children. Several similar Oidium-forms are parasites on the skin and hair of human beings, and produce skin diseases, such as scurvy (O. schoenleinii) and ringworm (O. tonsurans).

3. Mycorhiza. These Fungi, which have been found on the roots of many trees and heath-plants, particularly Cupuliferæ and Ericaceæ, consist of septate hyphæ, and belong partly to the Hymenomycetes, partly to the Gasteromycetes. It has been shown that the Mycorhiza enters into a symbiotic relationship with the roots of higher plants.

In this Division a well-marked alternation of generations is to be found. The development of the first or sexual generation (gametophyte),[16] which bears the sexual organs, antheridia and archegonia, commences with the germination of the spore, and consists, in the Liverworts, of a thallus, but in the true Mosses of a filamentous protonema, from which the Moss-plant arises as a lateral bud. The second or asexual generation (sporophyte), developed from the fertilised oosphere, consists of a sporangium and stalk.

The sexual generation, the gametophyte. The protonema in the Liverworts is very insignificant, and not always very sharply demarcated from the more highly developed parts of the nutritive system. In the true Mosses the protonema is well-developed, and consists of a branched, alga-like filament of cells, the dividing cell-walls being always placed obliquely. In the parts exposed to the light it is green, but colourless or brownish in those parts which are underground (Fig. 186). The protonema is considered to be a lower form of the stem, and grows in the same manner by means of an apical cell; at its apex it may directly develope into a leaf-bearing stem, or these arise from it as lateral branches (Fig. 186 k).

The more highly differentiated part of the vegetative system, the “Moss-plant,” which is thus developed from the protonema, is in the “thalloid” Liverworts generally a dichotomously-branched thallus without any trace of leaf-structures (Fig. 194); in Marchantia (Fig. 197) and others, scale-like leaves (amphigastria) are found on the under surface. The higher Liverworts and the Leafy-Mosses are differentiated into a filamentous, ramified stem with distinct leaves arranged in a definite manner, resembling the stem and leaves of the higher plants (Figs. 186, 195, 200).

[182]

True roots are wanting, but are biologically replaced by rhizoids. These are developed on the stems or thallus: in the Liverworts they are unicellular, but in the Leafy-Mosses generally multicellular and branched. In the latter group they are considered identical with the protonema, and may become true protonema, and new plants may be developed from them (Fig. 186 b).

Fig. 186.—A Lower portion of a Moss-plant with rhizoids (r), one of which bears a reproductive bud (b). The dotted line indicates the surface of the ground; the portions projecting above this become green protonema (p); k is a young Moss-plant formed on one of these. B Germinating spore of Funaria hygrometrica, with exospore still attached. C, D Older stages of the protonema.

The internal structure of the sexual generation is very simple. The leaves in nearly all cases are formed of a single-layered plate of cells; in the Leafy-Mosses, however, a midrib is very often formed, and sometimes, also, marginal veins; and along these lines the leaves are several layers of cells in thickness. The stem is constructed of cells longitudinally elongated, the external ones of which are narrower and sometimes have thicker walls than the more central ones. Vessels are not found, but in several Mosses there is in the centre of the stem a conducting strand of narrow, longitudinal cells, which represents the vascular bundle in its first[183] stage of development. This strand contains elements for conveying water as well as sieve-tubes. Stomata are entirely wanting in the sexual generation of the Leafy-Mosses; they are found in a few Liverworts (Marchantia), but their structure is not the same as in the higher plants.

Vegetative reproduction takes place by gemmæ or buds which arise on the protenema, the rhizoids, the thallus, or the shoots, and become detached from the mother-plant; or else the protonema and the older parts of the plant simply die off, and their branches thus become independent plants. This well-developed vegetative reproduction explains why so many Mosses grow gregariously. In certain Marchantiaceæ special cupules, in which gemmæ are developed, are found on the surface of the thallus (Fig. 197 A, s-s). Again, protonema may also arise from the leaves, and thus the leaves may act as reproductive bodies. Certain Mosses nearly always reproduce vegetatively, and in these species the oospheres are seldom fertilised.

Fig. 187.—Marchantia polymorpha: a mature antheridium.

Fig. 188.—Spermatozoids.

The first generation bears the SEXUAL ORGANS; both kinds are found either on the same plant (monœcious), or on separate plants (diœcious). In the thalloid Liverworts they are often situated on the apex of small stems (gametophores), springing from the surface of the thallus. In the Leafy-Liverworts and true Mosses the leaves which enclose the sexual organs often assume a peculiar shape, and are arranged more closely than the other leaves to form the so-called “Moss-flower.” The male sexual organs are called antheridia. They are stalked, spheroid, club- or egg-shaped bodies whose walls are formed of one layer of cells (Fig. 187), enclosing a mass of minute cubical cells, each one of which is a mother-cell of[184] a spermatozoid. The spermatozoids are self-motile; they are slightly twisted, with two cilia placed anteriorly (Fig. 188), while posteriorly they are generally a trifle club-shaped, and often bear at that part the remains of the cytoplasm, the spermatozoid itself being formed from the nucleus. In the presence of water the ripe antheridium bursts, and its contents are ejected; the spermatozoids, being liberated from their mother-cells, swarm about in the water in order to effect fertilisation.

Fig. 189.—Marchantia polymorpha. A A young, and B a ripe archegonium with open neck. C An unripe sporangium enclosed by the archegonium a: st the stalk; f the wall of the sporangium. Elaters are seen between the rows of spores.

The female sexual organs are termed archegonia. They are flask-shaped bodies (Fig. 189), the lower, swollen portion (venter) having a wall, in most cases from 1–2 cells thick, enclosing the oosphere (Fig. 189 B, k): the long neck is formed of tiers of 4–6 cells, enclosing a central row of cells—the neck-canal-cells (Fig. 189 A). When the archegonium is fully developed, the walls of the neck-canal-cells become mucilaginous and force open the neck of the archegonium. The mucilage thus escapes, and, remaining at the mouth of the archegonium, acts in a somewhat similar manner to the stigma and conducting tissue of a carpel, by catching and conducting the spermatozoids to the oosphere (Fig. 189 B, m), with[185] whose cell-nucleus they coalesce. With regard to the formation of the oosphere, it may further be remarked that the lower part of the archegonium originally encloses the so-called “central cell”; but shortly before the archegonium is ripe, this cuts off a small portion, the ventral-canal-cell, which lies immediately beneath the neck, and the larger, lower portion becomes the oosphere.

The fertilisation of the Mosses cannot be effected without water. Rain and dew therefore play a very important part in this process, and for this end various modifications of structure are found.

Fig. 190.—Andreæa rupestris. Longitudinal section through a sporangium at the time when the mother-cells of the spores are dividing: p pseudopodium; f foot; v vaginula; h neck; c columella; w wall of the sporangium; e external row of cells; s the spore-sac; t the spore-mother-cells; r the calyptra with the neck of archegonium (z).

Fig. 191.—Andreæa rupestris. Transverse section through a ripe sporangium. In the middle is seen the four-sided columella, surrounded by the numerous spores, drawn diagrammatically. Surrounding them is seen the wall of the sporangium, whose outer layer of cells is thickened and coloured. The layer of cells is unthickened in four places (x), indicating the position of the clefts (see Fig. 193).

[186]

Among the sexual organs, paraphyses—filamentous or club-shaped bodies—are to be found.

The asexual generation, the sporophyte (Moss-fruit or sporogonium). As the result of fertilisation the oosphere surrounds itself with a cell-wall, and then commences to divide in accordance with definite laws.[17] The embryo (Fig. 189 C) produced by these divisions remains inside the wall a-a of the archegonium (Figs. 190, 199 D, E), and developes into the sporogonium, which remains attached to the mother-plant, often nourished by it, as if the two were one organism. The lower extremity of the sporogonium, the foot (Figs. 190 f; 199 D), very often forces its way deep down into the tissue of the mother-plant, but without an actual union taking place. The central portion of the sporogonium becomes a shorter or longer stalk (seta), while the sporangium itself is developed at the summit. At a later stage, during the formation of the spores, the sporangium very often assumes the form of a capsule, and dehisces in several ways characteristic of the various genera (Figs. 192, 193, 194, 195, 200). The basal portion of the archegonium grows for a longer or shorter period, forming a sheath, the calyptra, in which the capsule is developed, but eventually it ceases to enlarge, and is then ruptured in different ways, but quite characteristically, in each group. Anatomically, the asexual generation is often more highly differentiated than the sexual; thus, for instance, stomata are present on the sporangia of the true Mosses, but are absent in the sexual generation.

As the capsule developes, an external layer of cells—the amphithecium—and an internal mass—the endothecium—are differentiated. As a rule the former becomes the wall of the capsule while the latter gives rise to the spores. In this Division, as in the Pteridophyta, the name archesporium (Fig. 190 t) is given to the group of cells inside the sporangium which gives rise to the mother-cells of the spores. The archesporium is in general a unicellular layer; in Sphagnum and Anthoceros it is derived from the most internal layer of the amphithecium, but with these exceptions it arises from the endothecium, usually from its most external layer. In the true Mosses and in Riccia only spore-mother-cells are produced from the archesporium, but in the[187] majority of the Liverworts some of these cells are sterile and become elaters (cells with spirally thickened walls, Figs. 196, 189), or serve as “nurse-cells” for the spore-mother-cells, which gradually absorb the nutriment which has been accumulated in them. In Anthoceros, and almost all the Leafy-Mosses, a certain mass of cells in the centre of the sporangium (derived from the endothecium) does not take part in the formation of the archesporium, but forms the so called “column” or “columella” (Figs. 190, 191).

The spores arise in tetrads, i.e. four in each mother-cell, and are arranged at the corners of a tetrahedron, each tetrahedron assuming the form of a sphere or a triangular pyramid. The mature spore is a nucleated mass of protoplasm, with starch or oil as reserve material. The wall is divided into two layers: the external coat (exospore) which is cuticularized and in most cases coloured (brown, yellowish), and the internal coat (endospore), which is colourless and not cuticularized. On germination the exospore is thrown off, the endospore protrudes, and cell-division commences and continues with the growth of the protonema (Fig. 186, B-D).

Fig. 192.—Andreæa petrophila. A ripe sporogonium: a an archegonium which has been raised with the pseudopodium; p the foot; b the neck; d-e the dark-coloured portion of the sporangium, whose outer cell-walls are considerably thickened; c-c the thin-walled portions where the dehiscence occurs; o the lower extremity of the spore-sac; f calyptra; g the apex of the sporangium. (Mag. 25 times.)

Fig. 193.—Andreæa petrophila. An empty capsule; the calyptra has fallen off. (Mag. 25 times.)

In the Liverworts the young sporogonium lives like a parasite, being nourished by the sexual generation (only in Anthoceros has it a slight power of assimilation). In the Leafy-Mosses, on the other hand, with regard to the power of assimilation, all transitions are found from abundant assimilation (Funaria, Physcomitrium) to almost complete “parasitism” (Sphagnum, Andreæa). In the majority of the operculate Mosses the sporogonium has a more or less perfect system of assimilation, and is able itself to form a large portion of the material necessary for the development of the spores, so that it chiefly receives from the sexual generation the inorganic substances which must be obtained from the soil. The more highly developed the assimilative system of the sporogonium, the more stomata are present.

The Mosses are the lowest plants which are provided with stem and leaf. They are assigned a lower place when compared with the higher Cryptogams, partly because there are still found within the Division so many forms with a mere thallus, partly because typical roots are wanting and the anatomical structure is so extremely simple, and partly also because of the relation between the two generations. The highest Mosses terminate the Division, the Muscineæ and Pteridophyta having had a common origin in the Algæ-like Thallophyta.

They are divided into two classes:—

Hepaticæ, or Liverworts.

Musci frondosi. True Mosses or Leafy-Mosses.

Class 1. Hepaticæ (Liverworts).

The protonema is only slightly developed. The remaining part of the vegetative body is either a prostrate, often dichotomously-branched thallus, pressed to the substratum (thalloid Liverworts), with or without scales on the under side (Figs. 194, 197); or a thin, prostrate, creeping stem, with distinctly-developed leaves, which are borne in two or three rows (Figs. 195, 198), viz., two on the upper and, in most cases, one on the under side. The leaves situated on the ventral side (amphigastria) are differently shaped from the others (Fig. 198 a), and are sometimes entirely absent.[189] In contradistinction to the Leafy-Mosses, stress must be laid on the well-marked dorsiventrality of the vegetative organs; i.e. the very distinct contrast between the dorsal side exposed to the light and the ventral side turned to the ground. Veins are never found in the leaves.

The ventral part of the archegonium (calyptra) continues to grow for some time, and encloses the growing embryo, but when the spores are ripe it is finally ruptured by the sporangium, and remains situated like a sheath (vaginula) around its base. The sporangium opens, longitudinally, by valves or teeth (Fig. 194, 195, 197 b), very rarely by a lid, or sometimes not at all. A columella is wanting (except in Anthoceros, Fig. 194); but on the other hand, a few of the cells lying between the spores are developed into elaters (Fig. 196), i.e. spindle-shaped cells with spirally-twisted thickenings, which are hygroscopic, and thus serve to distribute the spores. (They are seen in Fig. 189 C, not yet fully developed, as long cells radiating from the base of the sporangium. They are wanting in Riccia).

Fig. 194.—Anthoceros lævis (nat. size): K-K capsules.

Fig. 195.—Plagiochila asplenioides: a unripe, and b an open capsule; p involucre. The ventral edge of each leaf is higher than its dorsal edge, and covered by the dorsal edge of the next one.

Fig. 196.—An elater with two spores.

[190]

The majority of the Liverworts are found in damp and shady places, pressed to the substratum; a few are found floating in fresh water.

Family 1. Marchantieæ.

This embraces only forms with a thallus, which is more or less distinctly dichotomously branched, in some, one or two rows of thin leaves are situated on its under surface. On the upper surface of the thallus are found large air-chambers.

Order 1. Ricciaceæ. The sporogonia are, with the exception of a few genera, situated singly on the surface of the thallus, and consist only of a capsule without foot or stalk. They always remain enclosed by the wall of the archegonium (calyptra), and open only by its dissolution. Elaters are not developed. Some genera are found floating like Duckweed.—Riccia glauca grows on damp clay soil. R. fluitans and R. natans float in stagnant waters.

Fig. 197.—Marchantia polymorpha. A Female plant (nat. size): a and b are archegoniophores in various stages of development; s cupules with gemmæ (see page 183). B An archegoniophore seen from below, the short-stalked sporangia are seen placed in 8–10 double rows. C Male plant, with a young and an older antheridiophore. D Antheridiophore halved vertically to show the antheridia (h); m the aperture of the pits in which they are sunk—the older ones to the left, the younger to the right.

Order 3. Marchantiaceæ, are large, fleshy forms. The[191] surface of the thallus is divided into small rhombic areas, in the centre of each of which is found a large, peculiarly constructed stoma (Fig. 197 A); beneath each of these a large air-cavity is to be found. From the floor of the air-cavity a number of alga-like cells project into it; these contain chlorophyll and are therefore the assimilating cells. The antheridia and archegonia are each found aggregated on specially formed branches (somewhat resembling Mushrooms) projecting from the surface of the thallus. The antheridia are developed on the upper surface (Fig. 197 C, D) and the archegonia on the lower (Fig. 197 A, B), near the centrally-placed stalk.

Marchantia polymorpha is diœcious (Fig. 197), and very common on damp places. Lunularia (South Europe), frequently found on flower-pots in conservatories; Preissia, Fegatella, Reboulia, Targionia.

Family 3. Jungermannieæ.

Some forms in this family have a thallus in which leaf-like structures are found (Blasia), while in others (e.g. Metzgeria, Pellia, Aneura) they are entirely absent. The majority, however, have round, thick stems, bearing dorsally two rows of leaves, and one row ventrally. Some of these have the leaves “underlying” (Fig. 195), while in others (Fig. 198) they are “overlying.” (See Figs. 195, 198, with explanation).

The sporangia are spherical, stalked, and situated singly on the apex of the branches, and open by four valves (in Sphærocarpus they are indehiscent).

Fig. 198.—Frullania dilatata. Portion of a branch seen from the under side: r and b are the anterior and posterior edges of the same dorsal leaf; a ventral leaves (amphigastria). The dorsal leaves are “overlying,” i.e. the anterior edge of the leaf overlaps the posterior edge of the preceding one.

All the species in this family were formerly reckoned as belonging to one genus, Jungermannia, but now they are divided into several, arranged as follows:—

[192]

I. Anacrogynæ. The archegonia are situated on the upper side of the thallus or stem, placed laterally, and covered by an “involucre,” formed by the calyptra together with the tissue of the stem or thallus.

a. Anelatereæ. Without any elaters: Sphærocarpus, Riella.

b. Elatereæ. α. Thalloid: Aneura pinguis, in damp situations; Metzgeria furcata, on trees; Pellia epiphylla, in damp situations; Blasia pusilla, on damp clay soil, in the shade (scales are present on the thallus). β. Foliose and not dorsiventral: Haplomitrium hookeri.

II. Acrogynæ. The apex of the stem or of certain branches is adapted for the formation of female shoots. The archegonia are most frequently aggregated on the apex of the shoots, and are encircled by their leaves (perichætium). Between these and the archegonia, enclosing the latter, a peculiar cup-shaped organ (the involucre) is formed. This group only includes leaf-bearing genera: Frullania, Radula, Madotheca, Ptilidium, Calypogeia, Lepidozia, Mastigobryum, Lophocolea, Jungermannia, Scapania, Plagiochila.

Class 2. Musci frondosi or veri (True Mosses).

In this class the protonema is well developed, and resembles a branched filamentous Alga, from which it can be easily distinguished by its oblique septa (in Sphagnum it is a cellular expansion). The Moss-plant, which is developed directly from the protonema, generally has an erect, thick, cylindrical stem similarly constructed on all sides. The leaves are arranged spirally, the most frequent divergence being 2/5 or 3/8 (Fig. 200 A). A midrib is often present and also marginal veins formed by longitudinally elongated cells; at these veins the leaf is more than one layer in thickness. In Leucobryum the leaves are generally constructed of more than one layer.

The stem grows by means of a three-sided, pyramidal, apical cell which gives rise to three rows of segments, each segment forming a leaf. The lateral branches arise from the lower portions of the segments, the upper portion of which does not take any part in the construction of the leaf. From their mode of origin the branches are not axillary, and differ in this respect from the Flowering-plants.

The ventral portion of the archegonium is very early ruptured[193] at its base by the growing sporogonium, upon which it remains, and it is thus raised into the air, forming a “hood,” the calyptra (Figs. 192; 200 B). In the Sphagnaceæ the hood is not present; in this order, as in the Liverworts, the archegonium remains at the base of the sporogonium. The sporangium opens by circumsessile dehiscence, the upper portion (operculum) being separated along a specially constructed ring of cells, and falls off like a “lid” (Fig. 200). Only in a few forms (families 2 and 3) does any variation of this take place. Elaters are never found, but (with the exception of Archidium) there is always present in the sporangium a central mass of cells, the columella, which take no part in the formation of the spores. The columella, in some, does not reach quite to the operculum and in these cases the spore-sac is bell-shaped and covers the columella (Andreæa, Fig. 190; Sphagnum, Fig. 199 D); but in the majority of Mosses the columella extends to the lid, so that the space containing the spores becomes a hollow cylinder.

The sporangium is generally raised on a long stalk; in the great majority this stalk is formed from the lower half of the oospore and belongs to the asexual generation—it is then known as the seta. In Andreæa and Sphagnum the seta is very short, and the sporangia are raised upon a long stalk (pseudopodium) developed from the summit of the sexual generation (Figs. 190, 192). In the latter figure an archegonium (a) is seen attached to the pseudopodium, having been carried up with this during the course of its development. The summit of the pseudopodium is enlarged to embrace the foot of the sporogonium (Figs. 192, 199 D).

Fig. 199.—Sphagnum acutifolium.—A The upper portion of a plant: a branches with antheridia; ch branches with terminal archegonia and perichætia; b the upper stemleaves. B A male branch whose leaves are partly taken off in order to show the antheridia. C Group of three archegonia: the central one (a) is formed from the apical cell. D Sporogonium in longitudinal section: the broad foot (sg’) is sunk in the vaginula, v; c calyptra; ar neck of the archegonium; ps pseudopodium. E ripe sporangium with operculum, and the remains of the archegonium situated on the pseudopodium which is still surrounded by the perichætium; to the left is a barren branch. F Portion of a foliage-leaf seen from above: l perforations; b chlorophyll-containing cells; s spiral thickenings.

Family 1. Sphagneæ (Bog-Mosses).

The protonema has been already described. The stem is regularly branched owing to the fact that a branch, or collection of branches, arises at every fourth leaf. These branches are closely covered with leaves, some are erect, while others hang down and surround the stem. No rhizoids are developed. These Mosses are of a whitish-green colour, and when water is present are always saturated with it like a sponge, the reason for this being found in the construction of the stem and leaves. The stems are covered by an external layer of large clear cells, without chlorophyll, but with annular or spiral thickenings on the walls, which are also[194] perforated by large holes. By means of capillary attraction, water is thus raised to the summit of the stem. Similarly constructed cells are also found in the leaves, but they are surrounded by a net of very narrow, chlorophyll-containing cells (Fig. 199 F), whose colour is thus to a great extent lost amongst those which are colourless. This anatomical structure is an essential condition for the formation of peat. The Bog-Mosses grow by preference on[195] moors, which they cover with a thick carpet saturated with water. The lower extremities of the plants perish very rapidly, and gradually become converted into peat, and the branches thus separated from each other become independent plants. The sporangia (Fig. 199 D, E) are spherical, but with a very short stalk. They open by a lid, but have no annulus. The archegonium (Fig. 199 C) persists at the base of the sporogonium as in the Liverworts. Only one genus, Sphagnum.

Family 4. Stegocarpeæ.

To this belong the majority of the Mosses, about 3,000 species.

The capsule opens as in Sphagnum by means of a lid (operculum), which is often prolonged into a beak. Round the mouth of the opened capsule, a number of peculiar yellow or red teeth are to be found. These constitute the peristome; their number is four, or a multiple of four (8, 16, 32 or 64). The form and thickenings of these teeth are widely different, and on this account are used by Systematists for the purposes of classification. In some Mosses (Fig. 200 C, D) there is a double row of teeth. Except in Tetraphis they are not formed from entire cells, but from the strongly thickened portions of the wall of certain layers of cells belonging to the lid, and persist when this falls off. They are strongly hygroscopic, and assist greatly in the ejection of the lid, in which operation they are considerably aided by a ring of elastic cells with thickened walls, situated in the wall of the lid near the base of the teeth. This ring is known as the annulus. The archegonium is raised into the air like a hood, the calyptra, which[196] either covers the sporangium on all sides (having the shape of a bell), or is split on one side (Fig. 200 B, h).

The family is divided into two groups: the Musci acrocarpi, the growth of whose main axis is limited and terminated by the formation of the sexual organs; and the Musci pleurocarpi, whose sporogonia are situated on special lateral shoots, while the growth of the main axis is unlimited.

Fig. 200.—A Hypnum populeum. B and C Sporangia, with hood (h), and operculum (l’), and without these (C), showing the peristome (p). D The mouth of the capsule of Fontinalis antipyretica.

A. Acrocarpi.

B. Pleurocarpi.

The alternation of generations is as distinct in this Division as in the Mosses, but the sexual generation consists of only a small thallus, the prothallium, which bears directly the sexual organs, antheridia and archegonia; and the asexual generation, which arises from the fertilisation of the oosphere, is no longer a single short-lived sporangium, but a highly developed, generally perennial, plant provided with stem, leaves and true roots (Ferns, Horsetails, etc.), the sporangia being borne on the leaves. In this latter generation the tissues are differentiated into epidermis, ground tissue and vascular tissue; in the last named the bundles are closed, and in the majority of cases concentric.

The sexual generation, gametophyte, or prothallium, is always a thallus, although not always green and leaf-like (Figs. 205, 215, 222, 229, 235, etc.) It is very small, even in cases where it attains the greatest development, and consists only of parenchymatous cells. The prothallium is nourished by hair-like roots (rhizoids) and has only a transitory existence, dying soon after the fertilisation of its oosphere.

The ANTHERIDIA exhibit great variations in structure which, however, must be considered as modifications of the fundamental type which is found in the Mosses. These modifications will be mentioned under the various families. The spermatozoids are always spirally-coiled, self-motile, protoplasmic bodies, with most frequently a large number of fine cilia on the anterior end (Figs. 206, 223, 234). They are formed principally from the nucleus of the mother-cell, and portions of the cytoplasm often remain for a time attached to their posterior end.

The ARCHEGONIA are more uniform throughout the entire Division, and more closely resemble those of the Mosses. They are, as in the previous Division, principally flask-shaped; but the[199] central portion, which encloses the oosphere, is always embedded in the tissue of the prothallium, so that the neck, which is formed of 4 rows of cells, projects above the surface (Figs. 201 ³, 222 h). The development of the archegonium in a Fern is seen in the accompanying figure (Fig. 201). The archegonium is developed from a surface cell, which divides into three cells by two walls in a direction parallel to the surface of the prothallium (Fig. 201). The most internal cell becomes the ventral portion of the archegonium. The external one (b) divides perpendicularly to the surface of the prothallium into four cells, which again divide parallel to the surface and form the neck (b, in 2 and 3). The intermediate cell projects upwards into the neck and divides into two, the lower one, after the separation of the ventral canal-cell, becoming the oosphere, and the upper one the neck-canal-cell (c, in 2 and 3).

Fig. 201.—Pteris serrulata. Development of archegonia.]

As in the Mosses, the divisional walls of the neck-canal-cells become mucilaginous, causing the rupture of the neck of the archegonium. Fertilisation takes place as in the Mosses, and the passage of the spermatozoids, along the neck, to the oosphere, has been observed. Water (rain or dew) is similarly necessary for the movements of the spermatozoids, and hence for fertilisation. The other classes of the Division chiefly deviate from the Ferns in having the archegonium sunk deeper into the prothallium, and the neck reduced in length (compare Fig. 201 with Figs. 216, 222, 235, 236).

[200]

According to the nature of the spores, the three classes of the Vascular Cryptogams are each divided into isosporous and heterosporous groups.

I. The isosporous Vascular Cryptogams have only one kind of spore. The prothallium developed from this is in some cases monœcious, bearing both antheridia and archegonia; but in others there is a distinct tendency for each prothallium to bear only antheridia or archegonia (diœcious)—true Ferns and Lycopodium.

In Equisetum there is only one kind of spore, but two kinds of prothallia are developed, one of which bears only antheridia (male), the other only archegonia (female); but the one that bears antheridia may be transformed into the one that bears archegonia and vice versa.

II. In the higher group, heterosporous Vascular Cryptogams (Selaginella and Isoëtes, etc.), there are two distinct kinds of spores, the small, microspores, and the large, macrospores. The microspores are male, and produce prothallia which bear only antheridia. The macrospores are female, and produce prothallia which bear only archegonia.

Corresponding to this difference in the spores, there is also found a difference in the development of the prothallium. In the Isosporeæ the prothallium is large, and either green, leaf-like, and provided with rhizoids (most of the Ferns, Horsetails, etc.), or subterranean, pale-coloured, and globular (Ophioglossum, Lycopodium). It lives vegetatively for a fairly long time, and generally produces a large and varying number of archegonia and antheridia. The prothallium in the Heterosporeæ is gradually more and more reduced, its independent and vegetative life becomes of less and less importance, it becomes more dependent on the mother-plant, and projects from the spore very slightly, or not at all. The antheridia and archegonia become reduced in number to one, and also degenerate in point of development.

It may here be remarked that the gradual development of the asexual generation, the development of the two kinds of spores, and the progressive reduction of the prothallium and sexual organs which is found in this Division, is continued to the Gymnosperms and Angiosperms. The microspores are in these called pollen-grains, and the male prothallium is very rudimentary. The macrospores are termed embryo-sacs, and the female prothallium, the endosperm.

The asexual generation, sporophyte. When the oosphere,[201] which in this case as in all others is a primordial cell, is fertilised, it surrounds itself with a cell-wall and commences to divide into a number of cells, to form the embryo.

Fig. 202.—Adiantum capillus veneris. Vertical section through a prothallium (f f), with a young plant attached on its under side (mag. about 10 times); r the first root, and b the first leaf of the young Fern-plant; m the foot. In the angle between m and b lies the apex of the stem: h the rhizoids of the prothallium; æ æ unfertilised archegonia.

In the Mosses the asexual generation is the sporogonium, which is limited in its development and in a great measure dependent upon the sexual generation, upon which it is situated; but in the Pteridophyta this generation is an independent and highly developed plant, provided with stem, leaf, and true roots, and has in many instances an unlimited development. The Pteridophyta are the lowest Division with true roots. The root which is first formed is very similar in nature to the primary root of the Monocotyledons; it very soon dies and is replaced by others which are more permanent, and developed upon the stem (adventitious roots); roots are wanting in Salvinia, Psilotum, and some Hymenophyllaceæ. The differentiation is, however, not so complete as in the Flowering-plants, and so many leafy forms are not found. The various members of these plants are anatomically much higher than in the[202] Mosses, having an epidermis, a ground tissue with variously differentiated cells, and a highly developed vascular system. The vascular bundles, like those in the Monocotyledons, are without cambium, and closed; they are therefore incapable of any increase in thickness. In general the bundles are concentric, with the bast round the wood (Fig. 203). The wood is almost entirely made up of scalariform tracheides.

Fig. 203.—Portion of the stem of a Fern. Above is seen the transverse section, with vascular bundles of different form and size. The rhombic figures on the side of the stem are leaf-scars.

It is a point of special interest, that the gigantic forms of Ferns, Equisetums, and Club-Mosses (which flourished in earlier geological periods, when these classes attained their highest development) possessed some means of increasing in thickness.

The sporangia are in all cases capsule-like, and burst open when ripe to eject the spores. They are nearly always situated on the leaves (in Lycopodiaceæ, in the axils of the leaves, or above these, on the stems themselves). In some forms (Leptosporangiatæ), the sporangia are developed from a single epidermal cell; in others (Eusporangiatæ), from a group of epidermal cells, or from cells which lie beneath the epidermis. In the first group a primitive mother-cell (archesporium) is formed, which divides commonly into sixteen special mother-cells. In the latter group, on the other hand, a number of primitive spore-mother-cells are developed. In each sporangium three different tissues are generally developed; an innermost sporogenous one (s in Fig. 204 A), which arises from the archesporangium; an outermost one, which forms the wall (a),[203] and may be one or, more rarely, several layers in thickness; and an intermediate one, the tapetum (Fig. 204 A, B, b t), which is rich in protoplasm, and whose cells are dissolved so that the spores float freely in the fluid thus provided. The spores arise as in the Mosses (in tetrads), by the cross-division of the special mother-cells, and according to the manner in which they are arranged in the mother-cell have either a tetrahedral form, with a large base resembling a segment of a ball, or are oblong (bilateral spores). Their construction is the same as in the Mosses (p. 187).

Fig. 204.—Selaginella inæqualifolia. A A young sporangium, which may develope either into a macro-, or a microsporangium. B A microsporangium.

The spore-formation in its earliest commencement takes place in the same way in the Isosporous and the Heterosporous Vascular Cryptogams; but from a certain point, after the tetrahedral division, a difference occurs with regard to the macrosporangia. All the spores formed in the microsporangium may complete their development; but those which are formed in the macrosporangium are generally aborted, with the exception of one or four, and these consequently attain a much larger size (see Fig. 239.—The series to the left are microsporangia; those to the right, macrosporangia).

The Vascular Cryptogams are divided into three large classes, in each of which a progressive development can be traced from the isosporous to the heterosporous forms, but some of these are now only known as fossils.

Class 1. Filicinæ (Ferns).—The stem is small in comparison with the leaves, and branches only seldom, and then by lateral shoots. The leaves are scattered, large, often deeply divided, and of various highly developed forms. The undeveloped leaves are rolled up in the bud, having what is termed circinate venation. The sporangia are situated on the edge or on the lower side of the leaves, those on which the sporangia are borne (sporophylls) being often the ordinary foliage-leaves; but in a few cases the fertile differ from the barren ones (a higher stage in development). The fertile leaves are not confined to definite parts of the shoot, and do not limit its growth. The archesporium is most frequently unicellular.

A. Isosporous: Sub-Class 1. Filices (True Ferns).

B. Heterosporous: Sub-Class 2. Hydropterideæ (Water Ferns).

Class 2. Equisetinæ (Horsetails), in its widest meaning.—The leaves in this class are small in comparison with the stem. They are arranged in whorls, and unite to form a sheath. The sporangia are situated on specially modified, shield-like leaves, which are closely packed together and form a “cone.” The cone is borne terminally, and limits the growth of the shoot. The sporangia are developed from a large group of epidermal cells, the archesporium being unicellular. The branches are arranged in whorls, and develope acropetally.

A. Isosporous: Sub-Class 1. Equisetaceæ. Existing forms.

B. Heterosporous: Sub-Class 2. Extinct forms.

[205]

Class 3. Lycopodinæ (Club-Mosses).—Roots generally branching dichotomously. The leaves are scattered or opposite, and in proportion to the stem very small, undivided, and simple. They are scale-like and triangular, tapering from a broad base to a point. The sporangia are situated singly (except in Psilotaceæ), and almost in every case on the upper side of the leaf or in the axil of a leaf; but in some cases they are borne on the stem, just above the leaf-axil. The sporangia arise from groups of epidermal cells. The sporophylls are often modified, and differ from the foliage-leaves; they are then arranged in cones placed terminally on branches, thus limiting their growth.

A. Isosporous: Sub-Class 1. Lycopodieæ.

B. Heterosporous: Sub-Class 2. Selaginelleæ.

Class 1. Filicinæ (Ferns).

The characteristics of this class have already been given on page 204.

The class is divided into two sub-classes:—

1. The True Ferns, Filices, have one kind of spore which generally developes monœcious prothallia, relatively large and green. The sporangia are most frequently situated in groups (sori), which are often covered but not enclosed by an indusium.

2. Water Ferns, Hydropteridæ, have microsporangia with many (4 × 16) microspores, and macrosporangia, each with one macrospore. The prothallium is small, and projects but slightly from the germinating spore. The sporangia are situated in groups (sori), which are either enclosed by an indusium, or enveloped in a portion of a leaf, to form “fruits” termed sporocarps.

Sub-Class 1. Filices (the True Ferns).

Of the eight orders (with about 4,000 species) comprised in this sub-class, the Polypodiaceæ is the largest (having about 2,800 species) and the most familiar; for this reason it will be taken as typical.

The sexual generation. When the spore germinates, the external covering (exospore) is ruptured, as in the Mosses. The internal cell-wall (endospore) grows out as a filament, which soon divides and gives rise to the prothallium, a flat, cellular expansion resembling the thallus of a Liverwort. In its fully developed state[206] the prothallium is generally heart-shaped, dark green, and provided with root-hairs, and it attains a diameter of about one centimetre (Fig. 205). It is formed of one layer of cells, except along the central line near the anterior depression, where it becomes several layers of cells in thickness, forming the “cushion,” on the lower side of which the archegonia are developed. The antheridia are first formed; they are thus found on the oldest parts of the prothallium, on its edge, or among the root-hairs. The archegonia are developed later, and are therefore found near the apex. Several tropical Ferns have prothallia[18] deviating from this typical form; Trichomanes (Order Hymenophyllaceæ) has filamentous, branched prothallia, which resemble the protonema of a Moss. Others, again, have strap-shaped prothallia, which resemble the thallus of certain Liverworts.

Fig. 205.—Prothallium (p p) of Maiden hair (Adiantum capillus veneris) with a young plant attached: b first leaf; w′ primary root; w″ adventitious roots; h h root-hairs of the prothallium (× abt. 30).

Fig. 206.—Antheridia of Maiden-hair (× 550). A Unripe; B ripe, but unopened; C open and ejecting the spermatozoids (s). Those which have been last ejected are still lying enclosed in their mother-cells, the others are coiled up and drag with them the cytoplasmic remains (b); f cells of the prothallium.

[207]

The ARCHEGONIA have been already mentioned (p. 199, Fig. 201). The ANTHERIDIA are hemispherical or slightly conical bodies (Fig. 206). They consist, as in the Mosses, of a wall formed by one layer of cells, which encloses a number of spermatozoid-mother-cells (A and B). The antheridia when ripe absorb water, and are ruptured, and the spirally-coiled spermatozoids liberated (Fig. 206 S). The spermatozoids have been observed to pass down the neck of the archegonium, and to fuse with the oosphere.

The asexual generation. The first leaf, the “cotyledon,” of the embryo developed from the oospore (Figs. 202, 205) is always small, and has a very simple shape. The leaves which occur later become more perfect, stage by stage, until the permanent form of leaf has been attained.—The STEM is most frequently a subterranean or a semi-aerial rhizome; it is only in the tropical, palm-like Tree-Ferns, that the stem raises itself high in the air and resembles that of a tree, with leaf-scars or with the remains of leaves attached (Figs. 207, 203); in certain species the stem is encased in a thick mat of aerial roots (Dicksonia antarctica). When the rhizome is horizontal the internodes are frequently elongated, and the leaves are arranged in two rows, as in Polypodium vulgare and in the Bracken-Fern (Pteridium aquilinum), etc.; it is also generally dorsiventral, having a dorsal side on which the leaves are situated, and a ventral side, different from the former, on which the roots are borne. When the stem ascends in an oblique direction, or is nearly vertical, its internodes are extremely short, and the leaves are arranged in a spiral line with a complicated phyllotaxis, e.g. in Athyrium filix-fœmina, Aspidium filix-mas, etc. The BRANCHING upon the whole is extremely slight, and is generally confined to the petiole (e.g. Aspid. filix-mas), or to the stem near the insertion of the leaves. Several species normally form buds on different parts of the lamina. The buds which are formed on the stem are not confined to the leaf-axil as in the higher plants. The Tree-Ferns, generally, do not branch at all.

The VASCULAR BUNDLES are concentric, with the wood surrounded by the soft bast. In transverse section they are seen as circles or irregularly-shaped figures (Fig. 203), the name of “King Charles and the Oak” (Bracken-Fern) having originated from the appearance which the bundles present in oblique section. In Osmunda they are collateral and resemble those of the Flowering-plants. Round each individual bundle is often a sheath of thick-walled, hard, brown, sclerenchymatous cells, which act as a mechanical[208] tissue; similar strands are also found in other parts of the stem.

Fig. 207.—Various Ferns (1, 2, 3, 4).

The LEAVES in nearly all species are only foliage-leaves, borne in a spiral. They have an apical growth which continues for a long time, and some require several years for their complete development. In the buds they are rolled up (circinate); not only the midrib, but also all the lateral veins, and even the terminal[209] portions of a leaf are sometimes rolled up together, the tissues of the leaf being already fully developed and only waiting to expand. The leaves are often excessively divided and compound, with pinnate branches, and have an epidermis with stomata and a well-developed system of venation. Stipules are only found in Marattiaceæ and Ophioglossaceæ.

Very often peculiar hairs or scales (paleæ, ramenta), dry, brown, flat and broad, are found on stem and leaf.

The SPORANGIA are small, round capsules, which, in a very large number of Ferns, are formed on the back, but more rarely on the edge of the ordinary foliage-leaves. It is very seldom that there is any difference in form between the barren foliage-leaves and the fertile leaves, as is found for example in Blechnum spicant or Struthiopteris; or that the fertile part of the leaf is differently constructed from the barren portion of the same leaf, as in the Royal-Fern (Osmunda). In such instances the mesophyll of the fertile parts is poorly developed.

The sporangia in the Polypodiaceæ are lens-shaped, with long stalk (Fig. 211 D): their wall consists of one cell-layer on which a single row of cells, passing vertically over the top (that is along the edge of the sporangium), is developed into the “ring” (annulus). The cells of the annulus are very much thickened on the inner and side walls, and are yellowish-brown. The thickened cells, however, do not entirely encircle the sporangium, and on one side, near the stalk, they pass over into large, flat, thin-walled cells. These form a weak point in the wall, and it is here that the sporangium is opened diagonally by the elongation of the annulus. The sporangium of the Polypodiaceæ opens as it dries. The cells of the annulus are very hygroscopic, and in straightening, the annulus bends back with a jerk, thus ejecting the spores to considerable distances. The cells of the annulus absorb water with great readiness. [The sporangium arises as a single epidermal cell, from which a basal stalk-cell is cut off. Three oblique cell-walls, intersecting near the base, are next formed in the upper cell, and a fourth between these and parallel to the free surface; an inner tetrahedral cell enclosed by four others is thus formed, the outer cells become the wall of the sporangium, while the inner cell, by a series of walls, parallel to its sides, cuts off a layer of cells which eventually form the tapetum, the remaining central cell constituting the archesporium.]

The SPORES are either oblong and bilateral, or they are tetrahedric[210] with curved sides, depending upon the way in which the tetrad division has taken place.

The sporangia are almost always situated on the nerves and gathered into groups, sori, which differ in form in the various genera. The sori, in many genera, may be covered by a scale-like structure, the indusium (Figs. 211 B, 212).

In the majority of cases, each sorus is situated on a small papilla (placenta, or receptacle), which is supplied by a small vascular bundle. Between the sporangia, hairs (paraphyses) are often situated, which spring either from the placenta or from the stalks of the sporangia.

Systematic Division. The Ferns may be divided into two groups, characterized by the structure and development of the sporangia. The sporangia in the Eusporangiatæ take their origin from a group of epidermal cells, and their walls are formed by several layers of cells. The archesporium is the (not tetrahedric) hypodermal terminal cell of the axial row of cells which give rise to the sporangium. In the Leptosporangiatæ the sporangia are developed from single epidermal cells, and their walls are uni-layered. The archesporium is a central, often tetrahedric cell, from which sixteen spore-mother-cells are developed.[19] It is difficult to say which form is the oldest (according to Prantl, those which have the sori on the nerve-endings); however, the Eusporangiatæ would seem to have made their appearance long before the others, and also well defined Marattiaceæ and Ophioglossaceæ occur in the Kulm and Coal period, before the true Polypodiaceæ.

About 4,000 species of Ferns are now existing, and they are found especially in tropical and sub-tropical forests.

Family 1. Eusporangiatæ.

Order 1. Ophioglossaceæ. The prothallium differs from that of all other Ferns in being subterranean, free from chlorophyll, pale and tuberous. The stem is extremely short, with short internodes, most frequently unbranched, vertical, and entirely buried in the ground (Fig. 208 st). In several species (among which are the native ones) one leaf is produced every year, which has taken three to four years for its development. In Botrychium a closed, sheath-like basal part of each leaf covers the subsequent leaves during their development. In Ophioglossum and[211] others each leaf has at its base an intrapetiolar, cap-like sheath, which protects the succeeding leaf. The leaves are of two kinds: (a) foliage, which in Ophioglossum vulgatum are lanceolate and entire, but in Botrychium however, are pinnate (b in Fig. 208 A, B); and (b) fertile, which are found facing the upper side of the foliage-leaves. These latter in Ophioglossum are undivided and spike-like (Fig. 209 A), but pinnate in Botrychium (Fig. 208 B). Each foliage and fertile leaf are branches from the same petiole. The large sporangia are placed laterally, and open by two valves. No annulus is formed (Fig. 209).—Ophioglossum reproduces vegetatively by adventitious buds on the roots.

Fig. 208.—A Ophioglossum vulgatum (Adder’s-tongue); B Botrychium lunaria (Moonwort), both natural size; r-r roots; bs leaf-stalk; st stem; b foliage-leaf; f fertile leaf.

Fig. 209.—Fertile leaf of Ophioglossum.

[212]

Three genera with about twelve species.

Order 2. Marattiaceæ are tropical Ferns, whose gigantic leaves resemble those of the Polypodiaceæ, but have stipules in addition. The sporangia are grouped in sori, situated on the lower side of the leaves, the sporangia in each sorus being arranged either in two rows or in a ring. In Angiopteris they are isolated (Fig. 210 A), but in the other species (Kaulfussia, Danæa, Marattia), they are united, and form “synangia” divided into a number of chambers corresponding to the sporangia. These open by clefts or pores. Marattia presents the highest development, as its sporangia are completely united in a capsule-like synangium, which is closed until maturity, and then opens by two valves. In each valve there is a row of three to eleven sporangia, each opening by a slit towards the inside (Fig. 210 B, C). An indusium encloses the sorus, except in Kaulfussia; it is formed of flat and lobed hairs, which resemble the hairs of the other portions of the leaves. In Angiopteris and Marattia the indusium is very rudimentary; in Danæa it forms a kind of cupule.

Fig. 210.—Sporangia of the Marattiaceæ: A Angiopteris; B and C Marattia; C is a half sorus with nine sporangia, each of which has opened by a longitudinal cleft.

Family 2. Leptosporangiatæ.

Order 1. Polypodiaceæ. Sporangia on the lower side of the leaves, stalked and provided with a vertical, incomplete annulus; dehiscing by a transverse cleft (Fig. 211 D).—The genera are distinguished by the form of the indusium and the position of the sori, etc.

[213]

1. The sporangia cover the entire lower surface of the leaf (Tropical America and Asia). Acrostichum, Platycerium.

2. Sori without indusia, circular or oval. Polypodium (Fig. 211 A). The leaves are most frequently situated in two rows on the dorsal side of the creeping rhizome, and fall off leaving a smooth scar behind.—P. vulgare, common in woods, on stones. (Phegopteris also has no indusium; see page 214).

3. The sporangia are situated in continuous lines just inside the margin of the leaf.—Pteris[20]: the sporangia form a continuous line along the entire margin of the leaf (Fig. 211 C), which bends over and covers the sporangia, forming a “false-indusium.” Pteridium has linear sori situated on a marginal vascular bundle, covered by two linear basal indusia, of which the outer is bent over like the edge of a leaf.—P. aquilinum (Bracken) has a wide-spreading rhizome with large alternate leaves, placed on opposite sides, at some distance apart. Only one leaf is developed from each branch every year.

Fig. 211.—Portions of leaves with sori. A Polypodium. B Aspidium. C Pteridium. D A sporangium of one of the Polypodiaceæ: r the annulus; s spores.

4. The sori are oval or linear, situated on one side of the vascular bundle.—Asplenium (Fig. 212 A): sori linear; indusium with one of its edges attached at the external side. A. ruta muraria (Wall-Rue); A. septentrionale; A. trichomanes.—Athyrium: sori linear or curved; A. filix-fœmina (Lady-Fern).—Scolopendrium[214] (Fig. 212 B): sori as in Asplenium, but situated in pairs across the lanceolate, entire leaves. Each sorus is covered on the external side by an indusium, whose free edges are parallel and approach each other. S. vulgare (Hart’s-tongue).—Blechnum (B. spicant, Hard Fern; the fertile leaves differ from the barren, the pinnæ being narrower, while the underside is almost entirely covered with sori, and hence they are of a much darker brownish hue than the barren ones).—Ceterach: indusium rudimentary or absent.

5. Sori circular and covered by a shield-like, or reniform indusium.—Aspidium (Fig. 211 B); the leaves wither away and leave no scar upon the root-stock. A. filix-mas (Male-Fern); A. spinulosum.—Phegopteris has no indusium, the withered bases of the leaf-stalks are persistent; P. dryopteris and P. polypodioides.

6. The indusium is situated below the sori, and has the shape of a one-sided scale (Cystopteris, Struthiopteris), or of a cup or cupule, which in Woodsia is sometimes fimbriate (Fig. 212 C, D).

Fig. 212.—A Asplenium. B Scolopendrium. C Woodsia; D single sorus of the same. E Cyathea: the sporangia have fallen off in the upper sori. (All magnified.)

This order is the greatest, comprising about 2,800 species, the majority being perennial plants. A few are large, and known as Tree-Ferns.

Fig. 213.—Gleichenia: A part of a leaf with sori; B a single sorus.

Sub-Class 2. Hydropterideæ (formerly Rhizocarpeæ), Water Ferns.

The following further characteristics must be added to those given on page 205:—

[216]

Fig. 214.—Salvinia natans: A microsporangium with germinating microspores and protruding prothallia (s); B a prothallium with the bicellular antheridium (s) growing out of the microsporangium; C the two cells of the antheridium have opened by transverse clefts; beneath is seen the microspores enclosed by the hardened mucilage; D spermatozoids still enclosed in the mother-cells.

Fig. 215.—Salvinia natans. A, B Female prothallia, f-f, protruding from the macrospore which is still enclosed in the macrosporangium; œ archegonia. C An embryo (× 16) still in connection with the spore (s): a the scutiform leaf; b-e the subsequent foliage-leaves, of which b and c stand singly, d-e-v in a whorl; v the submerged-leaf; f-f wing-like lobes of the prothallium: m the foot.

Sexual generation. The MICROSPORES produce an extremely rudimentary prothallium, formed of only a single cell, and having also a very much reduced bicellular antheridium with a small number of spermatozoid mother-cells in each cell (in Salvinia 4, in Marsilia and Pilularia 16). In Salvinia the microspores remain embedded in a hard mucilaginous mass (at first frothy) which fills up the cavity of the sporangium. The prothallium must therefore[217] grow out through this slime and also through the wall of the sporangium (Fig. 214), and it thus terminates in a relatively long cell.

In Marsilia the microspores are set free from the microsporangium, and the prothallia, with the antheridia, remain in them until the spermatozoids are liberated. The latter are spirally-twisted threads.

The MACROSPORES, on germination, give rise to a very reduced prothallium, which in Salvinia bears 3 archegonia; but, if these are not fertilised, the prothallium may continue to grow and become a fairly large, green body with several archegonia (Fig. 215 A, B). In Marsilia the prothallium is still more reduced, it is enclosed in the macrospore, and only bears one archegonium. The archegonia are similar in structure to those of the Ferns, but are smaller, and sunk more deeply in the tissue of the prothallium.

Fig. 216.—Salvinia natans. A An archegonium, unripe, seen in longitudinal section: h the neck-cells; k the neck-canal-cells; c the central cell. B An open archegonium of which the neck-cells have separated off. C An open, old archegonium seen from the top.

The asexual generation is developed from the fertilised egg-cell. It is a dorsiventral, horizontal shoot. In Salvinia it bears at first a shield-like leaf, the scutiform leaf (Fig. 215 C, a), which is succeeded by the ordinary foliage-leaves. The young plants of Marsilia, likewise, have less perfect leaves in the very early stage.

The formation of the sporangium is the same as in the Leptosporangiate Ferns. (The 16 spore-mother-cells originate from one central, tetrahedric archesporium.)

The Hydropterideæ are divided into 2 orders, the chief differences between them being found in the asexual generation.

[218]

Fig. 217.—Salvinia natans (natural size): A seen from above, floating on the water; B a portion seen from the side in its natural position in the water.

Fig. 218.—Sori of Salvinia in longitudinal section: h microsporangia; m macrosporangia. (× 10.)

Order 1. Salviniaceæ. This order more nearly approaches the true Ferns, especially so on account of the form of the indusium. Only one species is found in Europe, Salvinia natans (Fig. 217). This is a small, floating, annual, aquatic plant, entirely destitute of roots. The dorsiventral, horizontal stem bears two kinds of leaves, which are arranged in whorls of three. Two of these which turn upwards are oval, entire, “aerial foliage-leaves” (Fig. 217 B, b²-b³); the third, the “water-leaf” (b¹) is submerged and divided into a number of hair-like segments, similar to the submerged leaves in many aquatic plants, for instance, Water-buttercup (see also Fig. 215 C). The whorls of leaves alternate with each other; there are thus 4 rows of dorsally-placed aerial leaves, and two rows of ventrally-placed submerged leaves. The sporangia are situated in sori, each sorus being borne on a small column (receptacle or placenta) and enveloped by a cupular, but entirely closed indusium (Fig. 218). The sori are situated on[219] the submerged leaves (Fig. 217 B, s-s) and are unisexual, i.e. each sorus contains microsporangia only, or macrosporangia.

Order 2. Marsiliaceæ. The characteristic feature of this order, and one not possessed by other Fern-like plants, is that the sori (2–many) are enveloped in leaf-segments which close round them and form a “sporocarp,” just in the same manner as the carpels, in the Angiospermous Flowering-plants, close round the ovules and form ovaries. The sori contain both micro-and macrosporangia. When the spores are ripe, the sporocarp opens in order to disperse the spores (Fig. 220).

Fig. 219.—Marsilia salvatrix (natural size): K terminal bud; b leaves; f sporocarps; x point of branching of petiole.

The two genera (with 57 species, Temperate, Tropics) are land-and marsh-plants, whose dorsiventral, creeping stem bears roots on the under surface, and the leaves in two rows on the upper side (Figs. 219, 221). The leaves of Marsilia are compound, and divided into four small leaflets springing from the apex of the petiole (Fig. 219), and resemble the leaves of Oxalis. In the bud the leaves are circinate (Fig. 219 b), and at night they exhibit the well-known sleep-movements. The sporocarps are borne on the petioles of the fertile leaves, near their bases (Fig. 219 f); they are oblong and resemble small beans, the outer cells being hard and sclerenchymatous, while the inner ones are divided into a number of loculi arranged in two rows. On[220] germination, water is absorbed, the two sides separate slightly, as valves (Fig. 220 A), and a long vermiform mass of gelatinous, parenchymatous cells (Fig. 220), swollen by the water, emerges, bearing a large number of sori arranged pinnately. Each sorus (sr) is covered by a thin indusium. (The thin covering may be considered an indusium physiologically, though not morphologically).