Frond simple, straight, much elongated, linear, constricted at the middle and truncate at the ends; segments usually inflated at the base.
Fronds simple, straight, much elongated, sometimes even twenty times longer than broad, constricted at the middle, where the suture is generally very distinct in both living and empty fronds. In almost every species the segments are inflated at the base; the ends are truncate.
Professor Bailey bas been very successful in adding new and curious species to this genus, some of them differing greatly from any previously known.
Docidium, like Closterium, has terminal globules containing moving granules, and its vesicles are either scattered or arranged in a single longitudinal row.
It differs from Closterium in its straight fronds and constricted middle; and from Penium it may be known by having a distant constriction at the middle and more elongated fronds.
1. D. nodulosum (Bréb.); frond stout; segments four to six times longer than broad, constricted at regular intervals so as to produce undulated margins; suture projecting on each side.
Closterium Trabecula, Bailey, Amer. Bacil. in Amer. Journ. of Science and Arts, v. 41. p. 302. t. 1. f. 32 ? (1841).
Docidium nodulosum, Brébisson, in lit. cum icone (1846).
Dolgelley, J. R. Durdham Down near Bristol, Mr. Thwaites. Aberdeenshire, Dr. Dickie and Mr. P. Grant. Ambleside, Westmoreland, Mr. Sidebotham. Henfield, Sussex, and near Southampton, Mr. Jenner.
Falaise, Brébisson. Maine to Virginia, Bailey.
Frond large, distinctly visible to the naked eye, beam-like, constricted at the middle, where the thickened suture projects on each side like an apiculus. Segments about four times as long as broad, scarcely attenuated, regularly inflated at intervals, whence the margins appear undulated; the basal inflation is the most prominent, the others less so as they are situated nearer the end; often only two or three nearest the base are distinct, but occasionally as many as eight undulations may he counted at the margin.
Docidium nodulosum differs from D. constrictum, Bailey, and D. nodosum, Bailey, in its more numerous but slighter constrictions. In both these species the inflations are always four, conspicuous, and more distant. In D. verrucosum, Bailey, the segments are longer in proportion to their breadth; the un-
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dulations, which are more numerous and equal, depend on the presence of whorls of small tubercles. In D. coronatum, Bréb., the apex being encircled by a series of small tubercles, the end view is crenate.
Length of frond 1/50 of an inch; breadth 1/428; breadth at inflation 1/393; breadth at end 1/625.
Tab. XXVI. fig. 1. a. frond with endochrome; b. empty frond.
2. D. truncatum (Bréb.); frond stout; segments three or four times longer than broad, with a single inflation at the base, tapering to the truncate entire ends; suture projecting on each side.
Carnarvon and Penzance, J. R. Hastings, Sussex, and Brookland near
Reigate, Surrey, Mr. Jenner.
Falaise, Brébisson. Germany, Kützing.
Frond cylindrical, stout, distinctly constricted at the middle, the suture forming a thickened rim, which projects on each side like a small point. Segments three or four times longer than broad, slightly inflated at the base and tapering towards the end, which is truncate and entire.
Docidium truncatum seems to me to approach closely to D. nodulosum, with which it agrees in size. Its distinctive marks are the more attenuated extremities and the solitary inflation at the base of each segment, so that its margins are not undulated. Mr. Jenner considers them as undoubtedly distinct, but to which dried specimens belong I am occasionally unable to decide; for in drying, fronds of D. nodulosum frequently become attenuated at the ends, and sometimes only the basal inflation can be seen. Its larger size, shortness of the segments in comparison with their breadth, and the distinct projection of the junction-rim on each side, sufficiently distinguish D. truncatum from D. Ehrenbergii.
Length of frond from 1/81 to 1/72 of an inch; greatest breadth from 1/526 to 1/439; breadth at constriction 1/591; breadth at end from 1/1168 to 1/940.
Tab. XXVI. fig. 2. a. frond with endochrome; b. empty frond.
Docidium truncatum, Brébisson, in lit. cum icone (1846).
3. D. clavatum (Kütz.); segments many times longer than broad, with a single inflation at the base; end clavate, but truncate at the apex.
Midhurst, Sussex, Mr. Jenner.
Germany, Kützing. Falaise, Brébisson.
Frond longer than those of the first two species, but more slender, constricted at the middle; the suture strongly marked, but not projecting at the margin.
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Docidium clavatum, Kützing, in lit. cum icone (1846). Brébisson, in lit. cum icone et specimine.
Segments eight to twelve times longer than broad, gradually thickened near the ends in a clavate manner, the end itself being slightly attenuated and truncate; there is a single inflation at the base. Vesicles small, few, and arranged in a single longitudinal line. The empty frond is minutely punctate, but the highest powers of the microscope are required to detect the puncta.
Brébisson's specimens are more clavate than British ones, or than Kützing's plant appears in a drawing received from him.
Length of frond 1/65 of an inch; breadth 1/813; breadth at inflation 1/909; breadth at end 1/1333.
Tab. XXVI. fig. 3. a. frond with endochrome; b. empty frond from French specimen.
4. D. Ehrenbergii --- ; segments many times longer than broad, having two or three slight inflations at the base and truncate ends bordered by minute tubercles.
beta. granulatum; frond rough with minute granules.
Closterium Trabecula, Ehr. Abh. d. Berl. Ak. (1830), p. 62; Infus. p. 93. t. 6. f. 2. Meneghini, Synop. Desmid. p. 235. Kützing, Phycologia Germanica, p. 133? Jenner, Flora of Tunbridge Wells, p. 196.
Dolgelley, Carnarvon, Penzance, &c., J. R. Several stations in Sussex; and near Southampton, Mr. Jenner. Aberdeenshire, Dr. Dickie and Mr. P. Grant. Ambleside, Mr. Sidebotham.
beta. Henfield, Sussex, Mr. Jenner. Penzance, J. R.
Germany, Ehrenberg, Kützing. Falaise, Brébisson.
Frond as long as those of Docidium nodulosum and D. truncatum, but far more slender, constricted at the middle; the suture strongly marked, but having no projection at the margins. Segments eight to twelve times longer than broad, having about two slight inflations at the base, but otherwise linear. The end is truncate, and three to five minute tubercles, which may be detected at its margin, give the end view a crenate appearance. The empty frond is punctate, but in general the puncta are not readily discerned. Mr. Jenner finds in Sussex a variety the frond of which is distinctly granulate.
I have gathered the sporangia at Penzance for two successive years; they are large, suborbicular or elliptic, but often slightly angular, and are situated between the conjugating fronds, from which they easily separate.
Docidium Ehrenbergii in size equals D. clavatum, but it is not clavate, and its ends are bordered by minute tubercles. In the latter character it corresponds with D. coronatum, Bréb.; but it is much smaller and the suture does not project at the sides.
Length of frond from 1/71 to 1/59 of an inch; breadth from 1/1111 to 1/961; breadth at inflation from 1/909 to 1/881; breadth at end 1/1184; diameter of sporangium 1/285.
Tab. XXVI. fig. 4. a. frond with endochrome; b. dividing frond; c. empty frond; d. conjugating fronds; e, f . sporangia.
Tab. XXXIII. fig. 4. empty frond of variety beta.
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5. D. Baculum (Bréb.); segments very slender, having a solitary and conspicuous inflation at the base, otherwise linear; vesicles in a single series.
Common. Carnarvon; Dolgelley; near Lampeter; Penzance, &c., J. R. Ashdown Forest; near Storrington, &c., Sussex, Mr. Jenner. Near Bristol, Mr. Thwaites and Mr. Broome. Aberdeenshire, Dr. Dickie and Mr. P. Grant. Ambleside, Mr. Sidebotham. Rochdale, Mr. Coates.
Falaise, Brébisson. Carlsbad and Prague, Corda. United States, Bailey.
Frond very slender, many times longer than broad, distinctly constricted at the middle. Suture strongly marked, but having no projections at the margins. Segments with a solitary inflation at the base, otherwise linear, the ends truncate and without tubercles.
Docidium Baculum may be readily recognized, as it is more slender than any of the preceding species, and its inflations are more developed.
Length of frond 1/111 of an inch; greatest breadth 1/1937; breadth at inflation 1/1938; breadth at end 1/2463.
Tab. XXXIII. fig. 5. a, b. fronds with endochrome; c. empty frond magnified 400 times.
6. D. minutum --- ; frond slender, slightly constricted at the middle; segments linear, not inflated; vesicles in a single series.
Dolgelley, J. R. New Forest, Hants; and Parham Old Park near Storrington, Sussex, Mr. Jenner.
Frond minute, smaller than those of any of the foregoing species, linear, the constriction often scarcely perceptible; segments four to six times longer than broad, the ends truncate.
The smaller size and uninflated state of Docidium minutum distinguish it from D. Baculum.
Length of frond 1/212 of an inch; greatest breadth 1/1582.
Tab. XXVI. fig. 5. a. frond with endochrome; b. empty frond.
7. D. ? asperum (Bréb.); frond slender, cylindrical, rough with minute scattered granules, neither constricted nor inflated at the middle; ends truncate and dilated.
Kerris near Penzance, J. R.
Falaise, Brébisson.
Frond slender, twelve or more times longer than broad, rough with scattered minute points which are best seen at the margins. Endochrome irregular. I have seen neither vesicles nor terminal globules.
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I am doubtful whether this plant be a true Docidium, for in all the other species of this genus there is, at the middle, an evident constriction, and a conspicuous suture where the segments eventually separate; on the other hand, this plant has neither constriction nor suture.
Specimens of Docidium asperum sent me by M. de Brébisson are attenuated towards the extremities, whilst the apex itself is dilated. British specimens are not constricted beneath the dilated ends. Brébisson finds moving granules at the extremities as in the other species, but I have not noticed them.
This plant is not unlike the separated joints of a species of Mougeotia, but the dilated ends and roughness produced by minute granules distinguish it.
Length of frond from 1/97 to 1/64 of an inch; breadth 1/2356; breadth at end 1/2272.
Tab. XXVI. fig. 6. a. frond with endochrome; b. empty frond; c. empty frond of French specimen.
