Frond simple, elongated, attenuated, lunately curved or arcuate, entire; the junction of the segments marked by a pale transverse band.
In Closterium the frond is simple, much elongated, fusiform, rarely cylindrical or prismatic, more or less attenuated at the extremities. It is semilunate, crescent-shaped, or, in a few instances, curved only at the ends, but in the usual position the opposite margins are always more or less dissimilar, the upper one being convex, and the lower, inclusive of the ends, straight, or more commonly concave; the lateral view, which differs from the front one, is straight and has both margins similar. As happens in the allied genera, the frond is composed of two segments which finally separate and allow the escape of the endochrome; the suture or junction is marked by a transverse hyaline or pale band, accompanied in some species by one or more transverse striae, best seen in the empty frond; but there is no constriction. The segments are entire, without spines, processes, or inflated protuberances.
The endochrome is green with darker longitudinal bands or fillets, the number of which varies in different species. Meneghini considers them of too much importance to be omitted in the specific definition*. They may occasionally be useful in discriminating nearly allied forms,
* " Interanea initio uniforma serius in taenias distribuuntur, quarum characteres constantes videntur et in specifica definitione omitti nequeunt." --- Menegh. Synop. Desmid. p. 230.
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but as they are frequently indistinct, or from various causes it may be difficult to count them with certainty, I am unwilling to introduce them into the specific character except in the absence of more permanent marks of distinction.
The diaphanous vesicles, which are conspicuous in most of the species, are either scattered or arranged, with more or less regularity, in a single longitudinal series.
At each extremity of the endochrome, even in its earliest state, there is a large hyaline or straw-coloured globule, which contains minute granules in constant motion. This globule disappears in the dried specimen.
A distinct circulation has been noticed in several species. It is said to occur only in specimens obtained from water, and not in those taken from moist ground.
The empty frond is striated in some species and smooth in others, but no instance of its being granulate is known. The striated species are by Ehrenberg placed together in a subgenus (Toxotium), but it is sometimes very difficult to detect the striae, which I have also seen distinctly in Closterium attenuatum, and other species usually considered smooth.
The colour and firmness of the covering differ in different species. Some are quite colourless, flexible, collapsing when dried, and in general allowing the endochrome to escape by a merely partial separation of the segments. These species are never striated. In other species the fronds are more or less straw-coloured or even reddish, probably from the presence of a small portion of silicate of iron. The deeper the colour the firmer is the frond. The segments separate entirely from each other and retain their shape when empty or dried; and some of the striated species, even when submitted to the action of nitric acid or fire, retain their form and markings. In the coloured species the extremities are generally darker than the rest of the frond.
Even in the firmest species the frond becomes flattened in drying, its breadth at the centre increases, and the ends appear more attenuated than in their living state. This fact should be attended to when describing or drawing a dried specimen.
In Closterium, of which several species have been noticed in a conjugated state, the process appears to be nearly the same as in the Conjugatae. Two fronds unite by means of projections arising at the
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junction of the two segments, and then the newly-formed portion continues to enlarge until the original segments are separated by a cell of an irregular four-sided figure. The contents of the fronds, being collected in this cell, become a dense seed-like mass, which is sometimes globular resembling the sporangium in Mougeotia, and sometimes square like that in Staurospermum. The newly-formed cell is thinner and generally paler than the segments of the frond; in some species it looks like a prolongation of the segments, and in others these are so loosely attached that their connection is scarcely perceptible.
Two species having cruciform or quadrate sporangia permanently attached to the empty segments of the conjugated fronds are separated by Kützing to form a new genus, Stauroceras. To these others have been added by Brébisson. Whilst fully admitting the soundness of the principle on which this separation has been made, I regret that I am unable to adopt it here, not only because I am uncertain to which genus some of the species should be referred, but because I have decided to employ in this monograph only such generic characters as can be determined in the ordinary state of the plant, and will not oblige the observer to depend on conditions which he may not be able to discover.
According to Meneghini the coupling of the fronds takes place from the convex margin. This is generally, but not invariably, the case, for I have observed that they are connected sometimes on the convex and sometimes on the concave margin; in some instances, in deed, I have seen the convex margin of one frond connected with the concave margin of another. Mr. Jenner has noticed the same diversity, but it appears to him to characterize different species.
As there is no constriction in Closterium, although its frond divides like that of other Desmidieae, the process of division is less evident. It is best seen in the striated species, in which the central suture is most distinct. The transverse line becomes double, and by the intermediate growth the frond at length consists of three portions. As the newly-formed central one continues to elongate, another transverse line becomes visible at its middle, where a complete separation at length takes place. At first however the new segment is often merely a rounded protuberance, and the frond is consequently unequal; and when it is perfected, if the covering is a coloured one, the newer segment can still be distinguished by its greater paleness.
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1. C. Lunula (Müller); frond smooth, semilunate; lower margin nearly straight, inclined upwards at the rounded ends; vesicles numerous, scattered.
Common. Carnarvon; Dolgelley; Penzance, &c., J. R. Several stations in Sussex, Kent, and Surrey, Mr. Jenner. Kerry Mr. Andrews. Aberdeenshire, Dr. Dickie and Mr. P. Grant. Near Congleton, Cheshire; Ambleside, and near Manchester, Mr. Sidebotham.
Germany, Kützing, Ehrenberg, Corda. Falaise, Brébisson. Common in New York and New England; Mexico, Bailey.
Frond bright green, stout, distinctly visible to the naked eye, semilunate, five or six times longer than broad; extremities conic with rounded and very obtuse ends. The upper margin is very convex, the lower straight, except at the extremities which incline upwards, so that the segments rapidly taper from their junction. Endochrome grass-green; fillets several, three more distinct than the rest; vesicles numerous, small and scattered.
The empty frond is colourless and without markings, and its sutur is indistinct or wanting. It shrinks in drying, and is destroyed by burning.
Closterium Lunula differs from C. Ehrenbergii and C. moniliferum in having no inflation at the middle of the lower margin; and although, in drying, it often acquires a prominent centre, its upward inclination at the extremities is a permanent mark of distinction. It may be known from C. acerosum by its stouter appearance and scattered vesicles.
I have never seen a specimen in which the length exceeded the breadth so much as in Ehrenberg's figure.
Meneghini refers C. Lunula of Kützing's 'Alg. Aq. Dul.' to Closterium moniliferum; but two specimens which I have had an opportunity of examining, one in a copy of that publication, and another given me by Kützing himself, belong to this species. I have therefore followed Ehrenberg in considering.
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the present as the plant of Nitzsch, whilst the figure in Kützing's 'Synopsis Diatomearum' must be referred to C. moniliferum.
Length of frond 1/62 of an inch; greatest breadth 1/330.
Tab. XXVII. fig. 1. a. front view; b. side view.
2. C. acerosum (Schrank); frond linear-lanceolate, gradually tapering; ends conical; fillets distinct; vesicles in a single series; empty frond colourless; striae none or indistinct.
Vibrio acerosus, Schrank, Faun. Boica, 3. 2. p. 47 (1803).
Closterium acerosum, Ehrenberg, Abhandl. der Berl. Akademie (1831); Infus. p. 92. t. 6. f. 1. Meneghini, Synop. Desmid. in Linnaea 1840, p. 233. Kützing, Phycologia Germanica, p. 131. Jenner, Fl. of Tunbridge Wells, p. 196. Hassall, British Freshwater Algae, p. 374.
Carnarvon; Dolgelley; and Penzance, J. R. Several stations in Sussex, and near Reigate, Surrey, Mr. Jenner. Cheshire and Westmoreland, Mr. Sidebotham. Manchester, Mr. Williamson. Aberdeenshire and Banffshire, Mr. P. Grant. Bristol, Mr. Thwaites.
beta. Brackish water at Shirehampton, near Bristol, Mr. Thwaites.
Germany, Ehrenberg, Kützing. Falaise, Brébisson. Mexico, Bailey.
Frond bright green, slender, six to twelve times longer than broad, linear-lanceolate; ends conical; lower margin nearly straight, except at the extremities, the conical form of which causes it to incline upwards; the upper margin slightly convex. Fillets three or more; vesicles arranged in a single longitudinal series.
The empty frond is colourless, and has a transverse line at the suture. This species is generally described as destitute of striae; but Mr. Jenner and myself have frequently detected them, although seldom distinctly. The striae are more evident in some specimens of beta.
Sporangia have been gathered by Mr. Jenner in Sussex; they are orbicular, and placed between the deciduous fronds.
Closterium acerosum differs from C. Lunula and C. lanceolatum in its more slender frond. Some states of it approach nearer to C. turgidum; it is usually however more slender, and its empty frond also is colourless, and its striae, whenever they occur, are very indistinct.
Length of frond from 1/170 to 1/58 of an inch; greatest breadth from 1/1103 to 1/582; diameter of sporangium 1/408.
Length of variety beta from 1/48 to 1/32; greatest breadth 1/510.
Tab. XXVII. fig. 2. a. front view of frond with endochrome; e, f , g. small states; b, d. empty fronds; h, i. conjugating fronds; k, l. perfect sporangia; m. germinated capsule?; c. frond of beta.
3. C. lanceolatum (Kütz.); frond semi-lanceolate, gradually tapering; ends subacute; fillets several; vesicles in a single series; empty frond colourless.
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Closterium tenue, Bailey, American Journal of Science and Arts, v. 41. p. 303. t. 1. f. 37 (1841)?
Closterium lanceolatum, Kützing, Phycologia Germanica, p. 130 (1845), in lit. cum icone. Brébisson, in lit.
About Lisburn; and near Belfast, Mr. D. Moore. Galway, Mr. M'Calla. Ambleside, Mr. Sidebotham. Westerham, Kent, Mr. Jenner.
West Point, New York, Bailey. Germany, Kützing. Falaise, Brébisson.
Frond semilanceolate, six to ten times longer than broad; stouter than that of Closterium acerosum; lower margin straight, but inclined upwards at each end owing to the tapering of the extremities; upper margin convex; fillets three op more; vesicles in a single longitudinal series. Empty frond usually colourless and destitute of striae.
Closterium lanceolatum is larger than C. acerosum; instead of being nearly alike, its margins, as stated above, differ considerably from each other, and its extremities are more tapering. It is distinguished from C. Lunula by having its vesicles in a single series, and its upper margin much less convex. Its ends are neither curved upwards, nor so obtuse as those of C. turgidum.
Length of frond 1/64 of an inch; greatest breadth 1/453.
Tab. XXVIII. fig. 1. a. frond with endochrome; b. empty frond.
4. C. turgidum (Ehr.); lower margin of frond slightly concave, inclined upwards at the rounded ends; upper margin with a depression near each extremity; empty frond coloured; striae numerous, fine but distinct.
Carnarvon; Dolgelley; Penzance, J. R. Sussex; Kent; Surrey; Hampshire, Mr. Jenner. Aberdeenshire, Dr. Dickie and Mr. P. Grant. Cheshire and Westmoreland, Mr. Sidebotham.
Germany, Ehrenberg. France, Brébisson.
Frond stout, visible to the naked eye, green, six to ten times longer than broad, semilanceolate; extremities curved upwards, ends broadly rounded. The lower margin is somewhat concave, but always sloped upwards at each end, where the upper margin, which is convex, has a slight depression in consequence of the inclination of the apex upwards. The vesicles form a single longitudinal series; fillets three or more.
The empty frond is reddish or straw-colour, and somewhat opake; the suture at the middle is distinct, and so are the longitudinal striae, which are numerous, close and fine.
The curved and rounded ends are characteristic of this species. Closterium decussatum, Kütz., differs in its more attenuated extremities.
Length of frond 1/39 of an inch; greatest breadth 1/370; distance between the striae 1/27200.
Tab. XXVII. fig. 3. a. frond with endochrome; b. empty fronds.
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††
Frond smooth, crescent-shaped, rapidly tapering from the middle.
5. C. Ehrenbergii (Menegh.); frond smooth, crescent-shaped, when empty colourless; lower margin inflated at the middle; ends rounded; vesicles numerous, scattered.
Common, often in streams. Henfield, Westham, Tunbridge Wells, &c., Sussex; Chertsey and Reigate, Surrey, Mr. Jenner. Penzance and Dolgelley, J. R. Bristol, Mr. Thwaites. Ambleside, Westmoreland, Mr. Sidebotham. Aberdeenshire and Banffshire, Mr. P. Grant.
Germany, Ehrenberg. Falaise, Brébisson.
Frond bright green, stout, distinctly visible to the naked eye, lunately curved, five or six times longer than broad, extremities tapering, ends rounded, lower margin very concave with an inflation at the middle; fillets several, three of them more evident; vesicles numerous, small and scattered. Empty frond colourless, without a suture at the middle, collapsing when dried.
Closterium Ehrenbergii agrees with C. Lunula and C. moniliferum in size, colour and texture: it is more curved than the former, the lower margin being concave, not straight, and its centre is protuberant. From the latter it differs in its vesicles, which are smaller, more numerous and scattered.
Length of frond 1/68 of an inch; greatest breadth 1/400.
Tab. XXVIII. fig. 2. frond with endochrome.
6. C. moniliferum (Bory); frond smooth, crescent-shaped, when empty colourless; lower margin inflated at the middle; ends rounded; vesicles in a single row.
Common. Penzance and Dolgelley, J. R. Framfield and Hastings, Sussex; and Reigate, Surrey, Mr. Jenner. Kerry, Mr. Andrews. Cheshunt, Mr. Hassall. Near Bristol, Mr. Thwaites. Yate, near Bristol, Mr. Broome. Aberdeenshire, Dr. Dickie and Mr. P. Grant. Banffshire, Mr. P. Grant. Cheshire and Westmoreland, Mr. Sidebotham. Manchester, Mr. Williamson.
Germany, Ehrenberg, Kützing, Corda, &c. Falaise, Brébisson. Common in New York and New England, Bailey.
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Frond bright green, stout, distinctly visible to the naked eye, lunately curved, five or six times longer than broad, extremities tapering, ends rounded; lower margin very concave, inflated at the middle; fillets several, one to three more distinct than the rest; vesicles few, large, and disposed in a single longitudinal series. The empty frond, colourless and without a suture at the middle, collapsing when dried.
Closterium moniliferum is smaller than C. Lunula and more curved, and it may always be distinguished by the inflation at the middle of its lower margin; its vesicles form a single series character which separates it also from C. Ehrenbergii.
Length of frond from 1/75 to 1/60 of an inch; greatest breadth from 1/510 to 1/466.
Tab. XXVIII. fig. 3. a. frond with endochrome; b. empty frond.
7. C. Jenneri --- ; frond crescent-shaped, generally slightly constricted at the suture, when empty colourless, rapidly tapering; ends very obtuse; vesicles in a single series.
Sussex; Surrey; and Hampshire, Mr. Jenner. Penzance, J. R.
Frond smaller than that of Closterium moniliferum, much curved; extremities tapering; ends rounded. There is generally a slight constriction at the suture. Fillets two or three. The empty frond colourless and without markings.
Closterium Jenneri is more curved than C. moniliferum, and there is no inflation of its lower margin. It is more curved than C. Leibleinii and C. Dianae, and its ends are far more obtuse than theirs.
Length between ends of frond 1/281 of an inch; breadth at suture 1/1730.
Tab. XXVIII. fig. 6. a, b. fronds with endochrome; c. empty frond.
8. C. Leibleinii (Kütz.); frond smooth, crescent-shaped; extremities much attenuated and subacute at the apex; lower margin slightly inflated at the middle; vesicles in a single row.
beta. More slender, the central inflation less evident; empty frond of a deeper colour and its central suture distinct.
Closterium Lunula, Leibl. Fl. 1827, p. 259. according to Kütz.
Closterium Leibleinii, Kützing, Synop. Diatom. in Linnaea 1833, p. 596; Phycol. Germ. p. 130. Brébisson, Alg. Fal. p. 58. t. 8. Meneghini, Synop. Desmid. in Linnaea 1840, p. 232.
Cheshire, Mr. Sidebotham. Albourn, Framfield, and Hastings, Sussex; and Reigate, Surrey, Mr. Jenner. Penzance and Dolgelley, J. R. Rochdale, Mr. Coates. Aberdeen, Mr. P. Grant. Shirehampton near Bristol, Mr. Thwaites.
Germany, Kützing. Falaise, Brébisson.
Frond small, crescent-shaped, stout, about four to eight times as long as
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broad; extremities tapering to a subacute apex. At the centre of the lower margin is a slight protuberance, which however is often nearly obsolete. Fillets frequently obscure; vesicles few, large, and disposed in a single series. The empty frond has generally a pale straw-colour tinge, and a transverse suture is usually visible at the centre.
Closterium Leibleinii much resembles a young specimen of C. moniliferum; but it is smaller and more curved, the ends are more acute, and the empty frond is usually coloured.
The variety beta. is nearly intermidiate between this and the following species.
I have gathered the sporangia at Penzance and Dolgelley; Mr. Jenner has found them in Sussex, and Mr. Thwaites near Bristol. They are orbicular, and but loosely connected with the empty segments of the fronds.
Length of frond from 1/291 to 1/165 of an inch; greatest breadth from 1/1632 to 1/582; length of sporangium from 1/1360 to 1/942; breadth from 1/2040 to 1/1275.
Tab. XXVIII. fig. 4. a, c, f, i, k. different states of frond with endochrome; h, d, e. empty fronds; g, h, l. sporangia.
9. C. Dianae (Ehr.); fronds smooth, slender-crescent-shaped; extremities tapering; apex subacute; lower margin not inflated; vesicles in a single series.
Sussex, Mr. Jenner, Dolgelley, J. R. Aberdeenshire, Dr. Dickie and Mr. P. Grant. Cheshire and Ambleside, Mr. Sidebotham.
Germany, Ehrenberg. Falaise, Brébisson.
Frond slender, six to eight times longer than broad, curved; extremities tapering to a subacute point. The lower margin is concave and not inflated at the centre. Fillets obscure; vesicles disposed in a single longitudinal series.
The empty frond has a pale straw-colour tint, and a transverse suture at the centre, where, as in C. Leibleinii, the segments easily separate.
This plant differs from C. Leibleinii in being longer, more slender and less curved, and in having no projection at the centre of the lower margin; yet I have doubts whether they are really distinct, as I have seen some specimens apparently intermediate.
Length between ends of frond 1/143 of an inch; greatest breadth 1/1275.
Tab. XXVIII. fig. 5. a, b. fronds with endochrome; c. empty frond.
†††
Closterium Dianae, Ehr. Infus. p. 92. t. 5. f. 17 (1838). Kützing, Phy. Germ. p. 130. Hassall, Brit. Freshwater Alg. p. 371.
10. C. didymotocum (Corda); frond nearly straight, broadly linear; extremities slightly tapering; ends truncate, reddish; fillets obscure.
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beta. Baillyanum (Bréb.); frond smaller with a suture only at the middle.
alpha. Rare. Dolgelley, J. R.
beta. Common. Dolgelley and Penzance, J. R. Sussex; Surrey; and Hampshire, Mr. Jenner. Aberdeenshire, Mr. P. Grant. Ambleside, Mr. Sidebotham.
Germany, Corda, Kützing. alpha. et beta . Falaise, Brébisson.
Frond six to ten times longer than broad, stout, nearly straight, equal except at the extremities, which taper more or less; ends truncate, fillets obscure; vesicles in a single longitudinal series; terminal globules and moving granules distinct.
Empty frond reddish, especially at the ends, where the colour is conspicuous even before the endochrome has collapsed. Faint striae may generally be detected in old specimens.
The variety beta. is by M. de Brébisson considered a distinct species. The only difference I can discover is in the number of sutures, and I doubt whether any dependence can be placed on this character. Closterium Baillyanum is also usually smaller than alpha, but not invariably, and before the escape of the endochrome I am unable to distinguish them even as varieties.
Closterium didymotocum may be known from all the preceding species by its straight frond combined with truncate ends. It differs from C. striolatum, C. intermedium, and C. angustatum, in the absence or indistinctness of its striae and the upward inclination of the lower margin at the extremities.
Length of frond in beta. 1/65 of an inch; breadth 1/813.
Tab. XXVIII. fig. 7. a. frond of alpha. with endochrome; b. empty frond; c. frond of beta. with endochrome; d. empty frond.
11. C. attenuatum (Ehr.); frond curved, attenuated, suddenly contracted at the end into a conical point; empty frond reddish, faintly striated.
Chiltington Common near Pulborough; Midhurst; Ashdown Forest; near Tunbridge Wells, &c. Sussex; Reigate, Surrey, Mr. Jenner. Dolgelley and Penzance, J. R. Ambleside, Mr. Sidebotham.
Berlin, Ehrenberg. Falaise, Brébisson.
Frond rather larger than that of Closterium striolatum, eight to twelve
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times longer than broad, curved, gradually attenuated, and at the end suddenly contracted into an obtuse, conical or subcylindrical point. Fillets obscure; vesicles in a single longitudinal series. Empty frond reddish, especially at the ends, transverse suture distinct. Longitudinal striae numerous, close, generally faint, but sometimes very distinct.
Closterium attenuatum might be supposed an incomplete state of another species, especially when its ends are dissimilar; but the sudden contraction of the extremities is a sufficient distinction.
Length of frond 1/57 of an inch; greatest breadth 1/669; distance between the striae 1/26315.
Tab. XXIX. fig. 5. a. frond with endochrome; b. empty frond.
12. C. costatum (Corda); frond stout, semilunate or crescent-shaped, tapering from the middle; ends obtuse; striae few and conspicuous; suture solitary.
Dolgelley; and Penzance, J. R. Sussex; Surrey; and Hampshire, Mr. Jenner. Aberdeenshire, Dr. Dickie and Mr. P. Grant. Ambleside, Mr. Sidebotham. Near Bristol, Mr. Broome.
Carlsbad; and Prague, Corda. Falaise, Brébisson.
Frond stout, five or six times longer than broad, crescent-shaped or nearly semilunate, rapidly attenuated from the centre; end obtuse or somewhat truncate. Fillets obscure; vesicles in a single series.
The empty frond is reddish, with a single transverse suture generally of two or more lines. The longitudinal striae, which are few compared to the breadth of the frond, are so very distinct that they may be counted without difficulty.
I have gathered a single sporangium at Dolgelley; it was orbicular, and resembled that of Closterium striolatum.
This species agrees with Closterium angustatum in its distinct, subdistant striae; but their forms are widely different. It is stouter in proportion to its length than either C. turgidum or C. striolatum, and its striae are much fewer than theirs.
Length of frond 1/75 of m inch; greatest breadth 1/384; distance of striae apart 1/5319.
Tab. XXIX. fig. 1. a. frond with endochrome; b. empty frond.
13. C. striolatum (Ehr.); frond closely but distinctly striated, semilunate or crescent-shaped, tapering from the middle; sutures generally three, never more.
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Common. Carnarvon; Dolgelley; Tal Sam near Lampeter; near Carmarthen; and Penzance, J. R. Sussex; Surrey; Kent; and Hampshire, Mr. Jenner. Kerry, Mr. Andrews. Galway, Mr. M'Calla. Hertfordshire, Mr. Hassall. Aberdeenshire, Dr. Dickie and Mr. P. Grant. Cheshire and Westmoreland, Mr. Sidebotham. Manchester, Mr. Gray and Mr. Williamson.
Germany, Ehrenberg. New York; and New England, Bailey. Falaise, Brébisson.
Frond six to twelve times longer than broad, very variable in both length and breadth, curved, tapering from the middle; ends very obtuse; upper margin convex; lower concave or straight, but never inclined upwards at the ends. Vesicles in a single series; fillets often obscure. This species forms yellowish-brown masses in the water.
The empty frond is reddish and darkest at the ends. Striae numerous, crowded, and easily detected. Sutures usually three, but sometimes only two: specimens with a single suture are very rare.
The sporangia, which are not uncommonly met with, are orbicular and placed between the deciduous fronds.
Closterium striolatum is shorter than C. turgidum, and the ends do not turn up; its striae are much more numerous and close than those of C. costatum; and both C. turgidum and C. costatum have constantly but a single suture. It is more closely striated than either C. intermedium or C. angustatum, and stouter also in proportion to its length. With this species C. didymotocum in some respects agrees as to its size and form, but it is straighter and less tapering, and its ends are more truncate, and the striae, if present, are detected with the greatest difficulty.
Length of frond from 1/80 to 1/68 of an inch; greatest breadth from 1/625 to 1/535; distance between the striae l/10000.
Tab. XXIX. fig. 2. a, b, c. fronds with endochrome; d, e, f . empty fronds; g, h. sporangia.
14. C. intermedium --- ; frond slender slightly curved, tapering; striae distinct, not crowded; sutures usually more than three.
Dolgelley, J. R.
Frond slender, nearly straight, many times longer than broad, very gradually tapering, ends truncate. Fillets obscure; vesicles in a single series. This species forms in the water large masses of a yellow-brown colour.
The empty frond is straw-colour; its striae are distinct and can be counted without difficulty. Sutures, though occasionally but three, are usually from four to seven in number. The central suture often forms a peliucid line resembling a dissepiment.
In its form and in the number of its striae Closterium intermedium is intermediate between C. striolatum and C. angustatum. According to M. de Brébisson, C. striolatum has about forty striae, C. intermedium twenty, and C.an-
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gustatum ten or twelve. The most remarkable feature in this plant is the number of its sutures exceeding that of any other species; it is more slender and tapers more gradually than C. striolatum. Its more numerous striae and tapering form distinguish it from C. angustatum.
Length of frond from 1/77 to 1/54 of an inch; greatest breadth 1/1073; distance between the striae 1/14571.
Tab. XXIX. fig. 3. a. frond with endochrome; b, c. empty fronds.
15. C. angustatum (Kütz.); frond sublinear, curved, scarcely attenuated; ends truncate; striae few, very distinct and prominent; sutures usually three.
Closterium angustatum, Kützing, Phycologia Germanica, p. 132 (1845); in lit. cum icone.
Closterium sulcatum, Brébisson, in lit. cum icone (1845).
Dolgelley, J. R. Waterdown Forest, &c., Sussex; Reigate, Surrey, Mr. Jenner. Aberdeenshire, Mr. P. Grant. Ambleside, Mr. Sidebotham.
Germany, Kützing. Falaise, Brébisson.
Frond curved, eight or more times longer than broad, nearly equal in breadth except towards the extremities which are somewhat attenuated, their ends however being truncate. The vesicles are arranged in a single longitudinal series; fillets obscure.
The empty frond is of a pale reddish colour and darkest at the ends. Transverse sutures usually three, the central one of two or more lines. The longitudinal striae, of which seldom more than three or four can be seen at one view, are few in number, very distinct and prominent, and not unfrequently somewhat spiral. The frond, I believe, has several angles or ridges, which under the glass have the effect of striae.
Its linear form and scarcely attenuated extremities distinguish this species from Closterium intermedium. The striae also are fewer in number, less crowded, and more distinct. C. angustatum differs from C. juncidum by its stouter form and more distinct striae; its upper margin also is convex, and not straight as in that species.
Length of frond 1/60 of an inch; greatest breadth 1/1142; distance between the striae 1/5000.
Tab. XXIX. fig. 4. a. frond with endochrome; b, c. empty fronds.
16. C. juncidum --- ; frond elongated, very slender, linear, straight except at the extremities, which are slightly attenuated and curved downwards.
alpha. Dolgelley and Penzance, J. R. Chiltington Common near Pulborough, Sussex, Mr. Jenner. Aberdeenshire, Dr. Dickie and Mr. P. Grant. Ambleside, Westmoreland; and Congleton, Cheshire, Mr. Sidebotham.
beta. Dolgelley, J. R. Midhurst, Sussex, Mr. Jenner.
Falaise, Brébisson.
Frond many times longer, than broad, very slender, linear, straight except
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at the extremities, which are slightly attenuated and curved downwards; ends obtuse. Fillets and vesicles none or obscure.
In alpha. the empty frond is nearly colourless, and the longitudinal striae are faint. In beta. the colour is deeper and the striae more conspicuous. Transverse sutures usually three.
I have gathered sporangia at Dolgelley and Penzance; they are orbicular and placed between the deciduous fronds.
The slender linear frond distinguishes this species.
Length of frond from 1/111 to 1/69 of an inch; breadth 1/5000; diameter of sporangium 1/672; distance between the striae 1/40000.
Length of beta. 1/144; breadth 1/2040; length of sporangium 1/625; breadth 1/688; breadth between the striae 1/27777.
Tab. XXIX. fig. 6. a. frond of alpha. with endochrome; b. empty frond; c, d. sporangia. Fig. 7. a. frond of beta. with endochrome; b. empty frond; c, d. sporangia.
17. C. lineatum (Ehr.); frond striated, slender, long, curved, gradually tapering into the conico-rostrate extremities; lower margin slightly inflated at its centre.
beta. Longitudinal striae spiral.
Closterium lineatum, Ehrenberg, Abhandl. der Berlin. Akademie 1833, p. 238; Infusor. p. 95. t. 6. f. 8. Meneghini, Synop. Desmid. in Linnaea 1840, p. 234. Kützing, Phycologia Germanica, p. 131. Jenner, Fl. of Tunbridge Wells, p. 196. Hassall, British Freshwater Algae, p. 372.
Closterium elongatum, Brébisson, Meneghini, Synopsis Desmid. p. 234 (1840).
Carnarvon; Dolgelley; and Penzance, J. R. Ashdown Forest, and Waterdown Forest, Sussex, Mr. Jenner. Aberdeenshire; and Banffshire, Mr. P. Grant. Manchester, Mr. Sidebotham.
Germany, Ehrenberg, Kützing. Falaise, Brébisson. Mexico, Bailey.
Frond large, twelve or more times longer than broad, slightly curved, lanceolate, gradually tapering into the slender extremities, which are curved downwards and obtuse at the end. The upper margin is slightly but uninterruptedly convex, so as to form an arc; the lower margin is concave, owing to the curved extremities, but it is slightly protuberant at the centre. Endochrome reaching nearly to the ends; fillets three or more, frequently obscure; vesicles in a single longitudinal series.
Empty frond of a pale straw-colour, with numerous but distinct longitudinal striae, and one or more transverse lines at the centre. Specimens occasionally are met with having the striae spirally arranged. This state, which is very beautiful, I can only regard as an accidental variety, as I have observed such a frond conjugated with one of the common kind.
Closterium lineatum connects the rostrate with the other striated species, as in general aspect it agrees with some of the latter, and in its inflated centre and tapering extremities with the former. It is liable to be mistaken for C. Ralfsii, but it is longer, more slender, less inflated at the centre, and more
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gradually attenuated; the colour too of its empty frond is paler, and its striae are not quite so crowded.
I have frequently gathered the sporangium near Dolgelley, and Mr. Jenner has gathered it in Sussex. It is very remarkable, being the only known example of a geminate or bilobed sporangium. The fronds approach and couple in the usual manner; but instead of the contents of both fronds uniting in the ordinary manner into a single body, a bilobed body is produced not unlike a species of Cosmarium in form. A distinct line is perceptible between the lobes or portions, and each resembles a globular or oval body flattened at the junction, and is formed by the contents of the adjacent segments. The sporangium is more closely connected with the conjugated fronds than is the case in species belonging to the first section, but the fronds are not permanently united to it as in Closterium rostratum. Although I have here called it bilobed, I regard the sporangium as binate, rather than bilobed, because it readily separates at the junction, each portion retaining the segments of the frond belonging to it.
Length of frond 1/48 of an inch; greatest breadth 1/909; length of the bilobed sporangium 1/173; greatest breadth 1/370; distance between the striae 1/26315.
Tab. XXX. fig. 1. a. frond with endochrome; b. empty frond; c. sporangium.
18. C. Ralfsii (Bréb.); frond stout, striated, curved, rapidly attenuated into linear beaks which are shorter than the ventricose body.
Closterium rostratum, Ralfs, in Jenner, Fl. of Tunbridge Wells, p. 196 (1845) (not of Ehrenberg according to Brébisson).
Closterium Ralfsii, Brébisson, in lit. (1845).
Stauroceras Ralfsii, Brébisson, in lit. (1846).
Carnarvon and Dolgelley, J. R. Midhurst; near Tunbridge Wells, &c., Mr. Jenner. Aberdeenshire, Dr. Dickie. Near Manchester; and Ambleside, Mr. Sidebotham.
Falaise, Brébisson.
Frond yellowish-brown, stout, six to eight times longer than broad; the upper margin convex, the lower concave, but ventricose at the centre; extremities tapering into a narrow linear beak, which is curved downwards, shorter than the body, and obtuse at the apex. Vesicles disposed rather irregularly in a single longitudinal series. Fillets generally obscure.
The empty frond, which is firm, is reddish, especially at the ends. Striae numerous, close, and distinct; transverse suture solitary.
This and the two following plants differ considerably from the other striated species (Closterium lineatum in some respects excepted). The body of the frond is somewhat lanceolate, being equally convex on both margins, and tapering at each end into a linear or setaceous beak, which is curved down-
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ward and thus gives the frond a curved appearance. The green endochrome is nearly confined to the inflated body.
Closterium Ralfsii may be known from C. rostratum and C. setaceum by its larger size, the deeper colour of its empty frond, the shortness of its beaks, its firmer texture, and by the upper margin, which, inclusive of the beaks, forms an uninterrupted convexity or arc.
Length of frond 1/79 of an inch; greatest breadth 1/526; distance between the striae 1/17241.
Tab. XXX. fig. 2. a. frond with endochrome; b. empty frond.
19. C. rostratum (Ehr.); frond striated, tapering at each end into a setaceous curved beak which is about equal in length to the ventricose body; sporangium cruciform.
Dolgelley and Penzance, J. R. Sussex; Kent, Mr. Jenner. Durdham Down near Bristol, Mr. Thwaites. Near Congleton, Cheshire; Ambleside, Westmoreland; and near Manchester, Mr. Sidebotham. Aberdeenshire, Mr. P. Grant.
Germany, Ehrenberg, Kützing, Corda. Falaise, Brébisson.
Frond lanceolate, tapering into setaceous beaks, which are curved downwards at the extremity, obtuse at the apex, and nearly equal in length to the inflated body.
Endochrome green, confined to the inflated portion; fillets obscure; vesicles arranged in a single series; the moving granules are situated at the end of the endochrome, and apparently are not contained within a globule, as their motion has a wider range than in many other species.
The empty frond is colourless or tinged straw-colour, and the striae are numerous and close.
Mr. Jenner and myself have gathered conjugated specimens of Closterium rostratum in greater abundance than those of any other species. The cell formed for the reception of the sporangium is intimately connected with the fronds, of which indeed it seems to form a part. When viewed in front it may be described as a four-sided figure, whose angles are cut off at their union with the segments. All its sides are concave, but those between the segments of the same frond are shorter than the others and have deeper and more angular concavities, so that the sporangium has the same figure as the cell.
Length of frond 1/69 of an inch; greatest breadth 1/1068; length of sporangium 1/714; breadth 1/346; distance between the striae 1/25000.
Tab. XXX. fig. 3. a. frond with endochrome; b, d. empty fronds; c. conjugated fronds; e. sporangium.
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20. C. setaceum (Ehr.); frond very slender, finely striated, narrow-lanceolate, tapering at each extremity into a very long setaceous beak, which alone is curved; vesicles none or obscure.
Closterium setaceum, Ehrenberg, Abhandl. der Berlin. Ak. 1833, p. 239; Infus. p. 97. t. 6. f. 11. Meneghini, Synop. Desmid. p. 235. Jenner, Fl. of Tunbridge Wells, p. 196. Hassall, Brit. Freshwater Algae, p. 373.
Closterium rostratum, Bailey, Amer. Bacillaria in Amer. Journ. of Science and Arts, v. 41. p. 303. t. 1. f. 36 (1841).
Stauroceras subulatum, Kützing, Phycologia Germanica, p. 133 (1845).
Stauroceras setaceum, Brébisson, in lit. (1846).
Dolgelley, J. R. Waterdown Forest; and near Cross-in-hand, Sussex, Mr. Jenner. near Bristol, Mr. Broome. Near Aberdeen, Mr. P. Grant.
Germany, Ehrenberg. Staten Island, New York, Bailey. Falaise, Brébisson.
Frond minute, many times longer than broad, very slender; the body narrow-lanceolate, straight, attenuated at each end into a setaceous beak or awn, which is longer than the inflated portion, curved downwards at the extremity and blunt at the apex. The endochrome is pale, and does not extend beyond the inflated part. Vesicles none or indistinct; fillets none; moving granules not contained within a globule.
The empty frond is colourless, and exhibits close and faint striae.
Conjugated specimens are not uncommon. The process differs but little from that described under the preceding species. The sporangium in this species also appears like a continuation of the segments, and is quadrate or cruciform.
Closterium setaceum may be known from C. rostratum and C. gracile by its slender beaks being longer than the body of the frond.
Length of frond 1/116 of an inch; greatest breadth 1/2381; distance between the striae 1/17857.
Tab. XXX. fig. 4. a. frond with endochrome; b. empty frond; c. sporangium.
21. C. Cornu (Ehr.); frond smooth, minute, curved, very slender; extremities slightly attenuated; ends obtuse; vesicles none or indistinct.
beta. Frond more turgid.
Closterium Cornu, Ehrenberg, Abhandl. der Berlin. Ak. p. 62 (1830); Infusor. p. 94. t. 6. f. 5. Meneghini, Synop. Desmid. in Linnaea 1840, p. 233. Jenner, Fl. of Tunbridge Wells, p. 196. Kützing, Phycologia Germanica, p. 131. Hassall, Brit. Freshwater Algae, p. 372.
Closterium tenue, Kützing, Synopsis Diatom. in Linnaea 1833, p. 595. f. 78; Phycologia Germanica, p. 130.
Henfield, Piltdown Common, Battle, and Backham Bogs, Sussex, Mr. Jenner.Dolgelley, J. R. Ambleside, Mr. Sidebotham.
Germany, Ehrenberg, Kützing. Falaise, Brébisson.
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Frond very minute, five to eight times longer than broad, slender, slightly curved; extremities attenuated; ends blunt, but frequently one more so than the other. The figure of the frond is variable; the upper margin is more or less convex, the lower one concave or straight; occasionally the extremities curve in opposite directions. Endochrome very pale. Vesicles wanting according to Meneghini; but Mr. Jenner informs me that they are present, although indistinct. The empty frond is colourless.
Mr. Jenner has gathered conjugated specimens at Rackham Bogs. The sporangium, which is quadrate, is large compared with the size of the plant. The empty segments of the frond remain attached to the angles of the sporangium.
Closterium Cornu differs from C. acutum in its obtuse ends.
Length of frond 1/140 of an inch; breadth 1/3709. Length of beta. 1/226; breadth 1/2142; length of sporangium 1/816 to 1/680; breadth 1/1133 to 1/906.
Tab. XXX. fig. 6. a, b. fronds of beta. with endochrome; c, d. front views of sporangia; e. side view of sporangium; f , g. fronds of alpha.
22. C. acutum (Lyngbye); frond curved, gradually tapering at each extremity; end more or less acute; empty frond colourless.
alpha. Frond six to twelve times longer than broad; ends subacute.
Echinella acuta, Lyngbye, Tent. Hydrophytologiae Danicae, p. 209. t. 69. G. (1819)
Frustulia acuta, Kützing, Synopsis Diatomearum in Linnaea 1833, p. 537.
Closterium acutum, Brébisson, in lit. cum icone (1845).
Stauroceras acutum, Brébisson, in lit. (1846).
beta. Frond ten to twenty times longer than broad, tapering at each extremity into a very fine point.
Frustulia subulata, Kützing, Synop. Diatom. p. 538. f. 3 (1833).
Stauroceras subulatum, Brébisson, in lit. cum icone (1846).
Dolgelley and Penzance, J. R. Rochdale, Mr. Coates. Brightling near Battle, Sussex, Mr. Jenner.
Germany, Kützing. Falaise, Brébisson.
Frond very minute and slender, many times longer than broad, narrow-lanceolate or acicular, slightly curved, gradually tapering; extremities hyaline, and more or less acute at the apex. Vesicles obscure; fillets none; endochrome very pale, and not extending to the extremities. The moving granules are free, and more or less remote from the ends.
The empty frond is quite colourless and free from markings.
Sporangia are not uncommon. I have frequently gathered them at Dolgelley and Penzance, and M. de Brébisson has sent me drawings of French specimens. The sporangium is cruciform in the front and oval in the side view. It is inclosed in a cell, similar to itself in form, but extending beyond it at the angles into the adjoining portion of the respective segments. In their empty state the segments have so much the colour and appearance of the water in which they are immersed that it is difficult to trace them, and the
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portions of the cell which project into the segments may be mistaken for them. The same circumstance renders it difficult to determine the exact form of the attenuated ends.
By Brébisson Closterium subulatum is regarded as a distinct species; and no doubt extreme states differ considerably, but I am unable to detect any distinctive character on which I can rely.
Closterium acutum differs from C. Cornu in its tapering frond and acute ends; its fronds are also far more closely united with the sporangium.
Length of frond 1/177 of an inch; greatest breadth 1/2550; length of sporangium 1/1131 to 1/645; breadth 1/2109.
Tab. XXX. fig. 5. a, b. fronds of alpha; c. frond of beta ; d. conjugated fronds from a drawing by Brébisson; e. front view of sporangium; f. side view of sporangium from a drawing by Brébisson.
Tab. XXXIV. fig. 5. sporangium.
