2. DIDYMOPRIUM, Kütz
Filament elongated, gelatinous, fragile, regularly twisted, cylindrical, with a bidentate process or angle on each side of the joint.
The filaments are elongated, simple, jointed, gelatinous and very fragile, and finally separate into single joints; each joint has two opposite bidentate angles or processes. Hence the margins of the filament are crenate; and as it is regularly twisted, it not only appears
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of unequal breadth, but the form of its joints also varies, as more or less of the angles is seen at the margin; in short, as they are at one time fully visible and at length entirely disappear.
In a transverse view the joints are circular or broadly elliptic, with two minute opposite projections which are formed by the angles.
The endochrome is radiate; its rays from four to seven.
Conjugated specimens of both species have been observed, and possess much interest from their being the representatives in this family of analogous states in some of the Conjugatae.
Didymoprium differs from Desmidium in having only two angles; in a transverse view also the number of rays of the endochrome does not depend on the number of angles.
Kützing separated this genus from Desmidium and Hyalotheca, and as this separation meets with the approbation of the Rev. M. J. Berkeley, I am induced, in deference to their joint opinion rather than from my own conviction of its necessity, to adopt it in the present work. Mr. Hassall is averse to its adoption; but surely he is mistaken when be puts the differential characters of Didymoprium and Desmidium on the same footing as the presence or absence of a mucous sheath, and thinks that if Didymoprium is a good and valid genus, the absence of a mucous sheath would be sufficient to separate from it Didymoprium Borreri.
The absence or presence of a mucous sheath, or rather its comparative development, since traces of it may be found in all the filamentous Desmidieae, can only be of specific value; and Mr. Hassall himself, in the analogous example of the Conjugatae, amongst which species of Tyndaridea and Mougeotia have equally developed sheaths, has only in one instance thought it necessary even to allude to its occurrence.
In addition to the characters already enumerated, I may observe that in Desmidium a transverse view shows that the cell itself, irrespective of the bidentate projections, is angular, and that the endochrome is divided into a number of rays corresponding with the number of angles : neither of these circumstances occurs in Didymoprium.
The filaments in this genus increase in length by the repeated division of the joints exactly as in the other genera, the new portions being formed between the original segments, which in other respects remain unaltered ; the teeth of the angles furnish a guide to the change
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that takes place, for they become more widely separated, and then the new teeth appear, very minute at first, but gradually enlarging, until the new segment equals the older one in breadth.
1. D. Grevillii (Kütz.); sheath distinct ; joints of the filament broader than long, with a thickened border at their junction; transverse view broadly elliptic.
Desmidium cylindricum, Greville, Scot. Crypt. Fl. t. 293. (1827); in Hook. Brit. Fl. v. 2. p. 402. Ag. Consp. Diatom. p. 56. Kützing, Synop. Diatom. in Linnaea 1833, p. 614. Brébisson, Alg. Fal. p. 64. Harv. Brit. Alg. p.197. Menegh. Synop. Desmid. in Linnaea 1844, p. 204. Ralfs, Annals of Nat. Hist. v. 11. p. 373. t. 8. f. 1; Trans. of Bot. Society of Edinburgh, v. 2. p. 6. t. 2. Hassall, Brit. Freshwater Algae, p. 342. t. 83. f. 1.
Appin, Capt. Carmichael. Dolgelley; Carnarvon; Penzance, &c., J. R.
Prussia, Kützing. Prague; Carlsbad; Reichenberg, &c., Corda. Falaise, Brébisson. New York; Rhodes Island, Bailey.
The filaments in Didymoprium Grevillii are as thick as those of Desmidium Swartzii, which in water is a very similar plant, and are very gelatinous and fragile; their colour is pale green, but, except when very young, somewhat opake. The joints are connected by a thickened border, and, inclusive of the angles, which are colourless, are rather broader than long, and oval ; the angles are bidentate, their teeth angular. When the angles are not visible the joints are nearly quadrate.
The mucous sheath is very evident, narrower in this plant than in Hyalotheca dissiliens, and waved at the margin. When the angles are not visible the undulation of the margin is slight, but becomes more marked as the angles become visible. The sheath is jointed as well as the filament, the lines of separation being sometimes distinctly apparent.
The filaments are regularly twisted, and at about every tenth joint the angles become very perceptible, whilst in the two central joints they are almost invisible; on slightly altering the position of the filament the angles in the latter become visible, and in the former disappear.
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On account of the oval form of the joints their respective angles are separated, and thus the filament acquires a pinnatifid appearance.
The transverse view is broadly elliptic, with a small process at each end, representing the angles. The mucous sheath is of the same form, and protuberant over the processes. The endochrome is four- or five-rayed.
I have gathered the conjugated state of Didymoprium Grevillii near Dolgelley. It has been found in France by M. de Brébisson, but I believe that the present is the first description of it.
Before coupling D. Grevillii separates into single joints (in only one instance have I observed two joints of one filament still united and conjugated with two other separated joints); the cells gape at the margins opposed to each other, exactly as described under Hyalotheca dissiliens, but to a smaller extent, and the original joint is far more easily detected, as one of the teeth of the angle bounds the cleft on each side. As the cleft is narrower, there is an absence of the notch-like appearance so evident on the outer margin of Hyalotheca dissiliens. The cells become connected by a narrow process, often remarkable for its length, and the contents of one cell passes through it into the other, and a sporangium is formed in the same manner as in many of the Conjugatae. The transfer of the endochrome takes place in a mass, and one part may frequently be observed uniting with that in the receiving-cell whilst the other is still in the tube. The joints couple in a crossed position, as in Hyalotheca dissiliens, but the length of the connecting tube permits them to remain apart. The joint which contains the sporangium is but little altered in a transverse view, and when the empty cell becomes detached can scarcely be distinguished, except by contrasting the denseness of the endochrome with its stellate appearance in the unconnected joints. This detachment of the empty cell is a frequent occurrence after the process is completed, and forms another character of resemblance to those Conjugatae which bear the sporangium within the cell.
In a front view the sporangium is as orbicular as the quadrate form of the joint will permit, being of course rather broader at the side which is cleft, and on that side is usually slightly protuberant. The mucous covering remains unaltered on the joints when they are coupled.
Length of joint 1/464 of an inch; breadth of filament including teeth 1/473; breadth of filament when the teeth are hidden, from 1/633 to 1/612; breadth of sheath from 1/409 to 1/312. Diameter of sporangium 1/573.
Tab. II. a. portion of a filament; b. dividing joint; c. separated joints; d. transverse view ; e, f , g. conjugated cells ; h, i, k. sporangia.
2. D. Borreri (Ralfs); joints inflated, barrel-shaped, longer than broad; transverse view circular.
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Bambusina Brebissonii, Kützing, Phycologia Germanica, p. 140 (1845).
Cwm Bychan, Mr. Borrer. Dolgelley; Llanberris; Tal Sarn near Lampeter, J. R. New Forest, Hants; near Battle; Ashdown Forest and Chiltington Common, Sussex, Mr. Jenner, Ireland, Mr. Andrews. Ambleside, Westmoreland, Mr. Sidebotham. Manchester, Mr. Willamson. Glen Lin, Dr. Dickie. Near Aberdeen; and Moss Hagg, Banffshire, Mr. P. Grant.
Falaise, Brébisson. Germany, Kützing. Rhodes Island, Bailey.
Filaments pale green, soon becoming slightly opake, very slender, their mucous sheath wanting or indistinct. In the water this species resembles Hyalotheca dissiliens, but it is less slippery to the touch, and by this character may often be known when unmixed with other Algae. The filaments are regularly twisted and complete a turn in about 16 joints. The latter are generally nearly twice as long as broad, but in some specimens their length scarcely exceeds their breadth; they are inflated, so that when the angles are not seen, they resemble small barrels placed end to end, but when the angles are fully displayed their appearance may be compared to the juxtaposition of flower-pots by their mouths, the rims and intervals between which will represent the crenate angles. The angles are bicrenate, and the crenatures being minute and rounded, seem less like an interruption of the outline than in D. Grevillii, but rather as if the angles were attached to the sides of the joints. On account of the length of the joints, the disposition of the endochrome in two portions is very distinct. The joints have not a thickened border at their junction as in D. Grevillii, and the filament separates with less facility into single joints. Occasionally, especially in the short-jointed variety, faint longitudinal lines interrupted at the suture may, on careful examination, be perceived, but I find them so uncertain and indistinct, even under the triplet, that I consider it advisable merely to allude to their occurrence ; I have however introduced a figure showing them as Mr. Jenner has observed them in favourable specimens with his powerful achromatic instrument. Mr. Jenner, to whom the credit of their discovery is due, does not find them in every specimen, and regards them as affording an excellent test of the power of the microscope. He informs me that they are situated upon the inner surface of the cell. The transverse view is circular, with two minute opposite projections. The endochrome, stellate as in the other species, has five or six rays.
The conjugated state of this species I have gathered sparingly at Dolgelley. We have seen that in this family D. Grevillii is the only known example which has the spore formed within the cell. D. Borreri presents us with another point of analogy between the Desmidieae and the Conjugatae. Most of the former have the frond composed of a single cell, or the filament before conjugating becomes altogether broken up; this is but imperfectly the case here, as the coupling cells have generally other cells remaining, attached either in an unaltered state, or conjugated on their part with portions of other filaments, and thus a kind of network is sometimes formed; the coupling of the cells crossways occasions a still more confused appearance and renders it exceedingly difficult to trace them. The process is similar to that described under Hyalotheca
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dissiliens, but the segments are still more widely separated on the inner side, and consequently so far thrown back as to cause the attached joints to form a zigzag. The elliptic sporangium lies between the cells, which remain permanently attached to it.
Kützing has established for this plant a distinct genus (Bambusina). The characters which he relies upon are the absence of a mucous sheath, the casklike joints, and their union, not by a thickened rim as in Didymoprium Grevillii, but in the manner of the Zygnemata. To these characters, if he had been acquainted with the reproductive state of the two plants, he would doubtless have added the different position of their sporangia.
Even if the presence of a sheath could be supposed to have a generic value, it would not apply to the present question ; for, as Mr. Jenner has pointed out to me, a mucous covering does exist, and may occasionally be detected as a narrow border to the filament. The agreement also between the plants in their angles and the regular twisting of their filaments appear to me to forbid their separation.
Kützing suggests * that this plant may be identical with the Gymnozyga moniliformis, Ehr. (Bericht d. Berl. Ac. Novb. 1840). I am unable to determine this point, as I have seen no other notice of Ehrenberg' s plant.
This plant was known to M. de Brébisson before it was described in the 'Annals of Natural History,' and indeed under the name of Desmidium bambusinum was included by him in a list of Desmidieae inserted in a treatise on the microscope by M. Chevalier in 1839, but I have retained the present name, it being the first under which it was either described or figured.
Length of joint 1/939 of an inch; breadth of the joint including teeth 1/1031. Length of sporangium 1/880, breadth 1/1106.
Tab. III. a, b. portions of mature filaments; c. portion of a filament with joints dividing; d, e, f . portions of filaments without endochrome to show the longitudinal markings; g, h. transverse views; i, k. portion of filaments conjugating; l, m. sporangia with the empty fronds attached.<
Arthrodesmus? cylindricus, Ehr. Infus. p. 142 (1838).
Hyalotheca cylindrica, Ehr. Kurze Nachricht über 274 seit dem Abschluss der Tafeln des grössern Infus. neu beobachtete Infus. (1840).
Desmidium compressum, Corda, Obser. micros. sur les Anim. de Carlsbad, p. 18 (1840).
Didymoprium Grevillii, Kützing, Phycologia Generalis, p. 166 (1843); Phy. Germ. p. 141.
Didymoprium cylindricum, Ralfs, Annals of Nat. Hist. v. 16. p. 10 (1845); Trans. of Bot. Soc. of Edinburgh, v. 2. p. 164.
Hyalotheca Grevillii, Brébisson in lit. (1846).
Chiltington Common near Pulborough, and Ashdown Forest, Sussex; near
Southampton, Hants, and Reigate, Surrey, Mr. Jenner, Cheshunt, Mr. Hassall. Meath, Mr. Moore. Aberdeenshire, Dr. Dickie and Mr. P. Grant.
Manchester, Mr. Williamson. Ambleside, Mr. Sidebotham.
Didymoprium Borreri, Ralfs, Annals of Nat. Hist. v. 16. p. 10 (1845);
Trans. of Bot. Society of Edinburgh, v. 2. p. 164. Jenner, Flora of Tunbridge Wells, p. 192.
Hyalotheca bambusina, Brébisson in lit. (1846).
