Frond simple, elongated, straight, not, or but slightly, constricted; segments entire.
The frond is cylindrical or elliptic and straight, with its opposite margins similar, its constriction none or very slight, and the suture at the junction of the segments is usually either indistinct or wanting. The segments are quite entire.
M. de Brébisson has constituted this genus for some plants which he separated from Closterium on account of their straight fronds, which have the opposite margins similar. It differs from Tetmemorus by the absence of a terminal notch, and from Cosmarium by its more elongated frond and its less marked constriction at the junction of the segments; yet the cylindrical species of Cosmarium closely approach to this genus, and Cosmarium turgidum and Cosmarium attenuatum are at least as much elongated as Penium truncatum.
Although the species in Penium are few, they present considerable differences in their characters. Some are smooth, and, like Closterium, have the endochrome arranged in longitudinal fillets, and at each extremity of it a globule containing moving granules. Other species have a granulated surface, and there are two smooth and truncate which some botanists have referred to the Palmelleae.
Penium Digitus, on account of its size, is represented as magnified only 200 diameters.
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* Empty frond either striate or granulate, generally reddish.
1. P. margaritaceum (Ehr.); frond cylindrical with rotundato-truncate ends; pearly granules in longitudinal series.
alpha. Frond fusiform, constricted at the middle; granules distinct, giving a denticulate appearance to the margin.
beta. Frond linear, scarcely constricted at the middle; granules giving a denticulate appearance to the margin, somewhat scattered near the suture.
gamma. punctatum; frond linear, neither constricted at the suture nor denticulate at the margin; granules appearing like puncta.
Closterium margaritaceum, Ehrenberg, Infus. p. 95. t. 6. f. 13 (1838). Meneghini, Synop. Desmid. p. 236. Jenner, Fl. of Tunbridge Wells, p. 196. Kützing, Phy. Germ. p. 132. Hassall, Brit. Freshwater Algae, p. 376.
alpha. Ashdown Forest, Sussex, Mr. Jenner. Penzance, J. R.
beta. Near Bristol, Mr. Thwaites. Warbleton, Sussex, Mr. Jenner.
gamma. Dolgelley, J. R. Ashdown Forest, and Henfield, Sussex; and Reigate, Surrey, Mr. Jenner. Near Aberdeen, Dr. Dickie and Mr. P. Grant. Ambleside, Mr. Sidebotham.
Berlin, Ehrenberg. Falaise, Brébisson.
Frond minute, six to twelve times longer than broad, rough with pearly granules which are arranged in longitudinal rows. The forms which I have here considered varieties differ so much, that it is probable they will prove to be distinct species. It will be seen that the variety beta. is intermediate between the extreme states, and since neither of our British forms agrees with Ehrenberg's figure and description, I shall describe each in detail.
alpha. Frond stout, rounded at the end, distinctly constricted at the middle; fillets distinct, interrupted and, as well as the endochrome, divided into four equal portions by three pale transverse bands. Near each extremity there is an obscure globule; segments somewhat fusiform. The empty frond is nearly colourless, and the pearly granules are distinct and give a denticulate appearance to the margin. Besides the middle transverse suture, there are two others corresponding with the interruptions of the endochrome. I have received this form from M. de Brébisson as his Penium margaritaceum. It differs from Ehrenberg's figure of Closterium margaritaceum in being broader, more constricted at the middle, and having more ventricose segments. The arrangement of the endochrome and the position of the globules also differ.
The variety beta. agrees in colour with the preceding, but it is shorter, and its sides are parallel. The granules are distinct, but less regular. I have only seen it after the endochrome had collapsed.
The variety gamma. is elongated, slender, linear, truncate at the ends, and scarcely constricted at the middle. The endochrome is divided into four portions by transverse pale bands; but there are no fillets or globules with moving particles. The empty frond is reddish, especially at its extremities, the last-formed segment being generally paler than the other. The pearly granules
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Penium margaritaceum, Brébisson, in lit. (1846).
are very minute, and resemble puncta; hence the margin of the frond is entire. The puncta or granules are arranged in longitudinal lines, but those in the same line are so close together that they are nearly, if not quite, confluent; in fact, unless a very high power of the microscope be used, the frond appears simply striate. Besides the central suture, several other transverse lines divide the empty frond into compartments. This form agrees best with Ehrenberg's figure of Closterium margaritaceum, but it is not denticulate at the margin.
Sporangia of gamma. have been gathered by myself near Dolgelley, and those of beta. by Mr. Thwaites near Bristol. Both are orbicular, and situate between the deciduous fronds.
Length of frond in alpha . 1/156 of an inch; breadth 1/961; breadth at constriction 1/1234; length of frond in gamma. 1/169; breadth 1/1515; diameter of sporangium 1/543.
Tab. XXV. fig. 1. a. frond of alpha. with endochrome; b, c. empty fronds; d. empty frond of gamma. as seen under a low power; e, f. fronds with endochrome; g, h. sporangia.
Tab. XXXIII. fig. 3. sporangium of beta
2. P. Cylindrus (Ehr.); frond cylindrical with rotundato-truncate ends, rough with scattered pearly granules.
Closterium? Cylindrus, Ehrenberg, Infus. p. 95. t. 6. f. 6 (1838). Meneghini, Synop. Desmid. p. 236. Kützing, Phy. Germ. p. 132.
Penium Cylindrus, Brébisson, in lit. (1846).
Dolgelley, J. R. Ambleside, Mr. Sidebotham. Henfield; Ashdown Forest, and Piltdown Common near Uckfield, Sussex, Mr. Jenner.
Berlin, Ehrenberg. Falaise, Brébisson.
Frond very minute, smaller than that of Penium margaritaceum, two or three times longer than broad, cylindrical with truncate ends, and rough with minute scattered granules or apiculi. As the covering is usually of a deep rusty red, it obscures the view of the endochrome. I have not observed any terminal globules.
Penium Cylindrus resembles P. margaritaceum in form, but is much smaller, and its pearly granules are scattered and not arranged in lines. The red colour of the empty frond is darker than that of any other plant in the family.
I have little hesitation in referring the British specimens to Ehrenberg's Closterium Cylindrus, although in their scattered granules they differ from his and Meneghini's descriptions.
Length of frond 1/492 of an inch; breadth 1/1760.
Tab. XXV. fig. 2. a. frond with endochrome; b. dividing frond; c. empty frond.
†
Sporangium situated between the deciduous cells.
3. P. Digitus ( Ehr.); frond smooth, elliptic-oblong with rounded ends; fillets obscure, undulated, interrupted only by a transverse band at the suture.
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Closterium Digitus, Ehr. Abh. der Berl. Ak.. (1831), p. 68; Infus. p. 94. t. 6. f. 3 ? Meneghini, Synop. Desmid. in Linnaea 1840, p. 236. Bailey, Amer. Bacil. in Amer. Journ. of Science and Arts, v. 41. p. 302. t. 1. f. 33. Jenner, Fl. of Tunbridge Wells, p. 196. Hassall, Brit. Alg. p. 376. Kützing, Phy. Germ. p. 132.
Closterium lamellosum, Brébisson, Alg. Fal. p. 59. t. 8 (1835).
Pleurosicyos myriopodus, Corda, Alm. de Carlsb. 1835, p. 125. t. 5. f. 68.
Penium Digitus, Brébisson, in lit. (1847).
Polysolenia Closterium, Ehr. MS. Bailey, in lit.
Very common. Wales and Penzance, J. R. Sussex, Surrey, Kent and Hants, Mr. Jenner. Kerry, Mr. Andrews. Near Bristol, Mr. Thwaites. Aberdeenshire, Dr. Dickie and Mr. P. Grant. Banffshire, Mr. P. Grant. Ambleside, Mr. Sidebotham.
Germany, Ehrenberg, Kützing, Corda. Falaise, Brébisson. Maine to Virginia, Bailey.
Frond smooth, stout, three to five times longer than broad, elliptic or elliptic-oblong; not unfrequently however the frond is dilated at one end and becomes ovato-oblong; the ends are broadly rounded. The endochrome is yellow-green with a pale transverse band at the middle; there are no regular fillets, but longitudinal undulations are more or less perceptible. Terminal globules wanting, or very indistinct, in British specimens. The end view is circular, and the endochrorne radiate. The empty frond is colourless, flexible, and without markings.
Ehrenberg's description and figure of his Closterium Digitus is unlike the plant here described, and Brébisson formerly supposed it was intended for the next species; but the whole outline and the description of the rounded ends are certainly more suitable to this. I have never seen any terminal vesicles, yet they are depicted by Ehrenberg and also by Professor Bailey in a figure in his 'American Bacillaria.'
In the recent state there can be no danger of confounding Penium digitus with P. interruptum; and even in the dried state, although the conspicuous differences dependent on the disposition of the endochrome are no longer to be found, the form of the frond appears to me a sufficient distinction.
Length of frond 1/81 of an inch; greatest breadth 1/299.
Tab. XXV. fig. 3. a, b. fronds with endochrome; c. empty frond.
4. P. interruptum (Bréb.); frond smooth, cylindrical; extremities conical with rounded apex; fillets strongly marked, interrupted by three transverse bands.
Dolgelley and Penzance, J. R. Ashdown Forest and Chiltington Common, Sussex, Mr. Jenner. Ambleside, Westmoreland, Mr. Sidebotham;
Falaise, Brébisson.
Frond stout, four to six times longer than broad, quite straight, cylindrical, so that the sides are parallel, except at the extremities, which are rather suddenly conical and rounded at the apex. Endochrome dark green; fillets straight, three or four strongly marked and a fainter one near each margin.
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Besides the central transverse band present in all the Desmidieae, Penium interruptum has two others; the fillets and endochrome are consequently divided into four portions. The ends are colourless, and each is partly occupied by a large globule, which contains moving granules like those in Closterium. The empty frond is colourless without markings, and there is no transverse line at the middle.
In a recent state this is a remarkable plant. The fillets are more strongly marked than in any other species I have met with, and the checkered appearance produced by the transverse bands essentially distinguish it. It must however be observed that this character is lost in the dried state, when its straight, cylindrical fronds have some similarity to those of Penium Digitus; but they are longer in proportion, their sides more parallel, and their extremities more conical.
Length of frond 1/116 of an inch; breadth 1/571.
Tab. XXV. fig. 4. a. frond magnified 400 times; b. frond magnified 200 times.
5. P. closterioides --- ; frond smooth, fusiform or lanceolate; longitudinal fillets and terminal globules distinct.
Penzance and Dolgelley, J. R. Ashdown Forest, and Piltdown, Sussex; Reigate, Surrey; and near Southampton, Mr. Jenner.
Frond six to ten times longer than broad, straight, lanceolate; end obtuse; fillets and terminal globules distinct; vesicles in a single longitudinal series. Empty frond colourless and without markings.
Penium closterioides in its appearance and in the arrangement of its endochrome agrees better with Closterium than with Penium, and strongly resembles the side view of some species of the former. The frond however is always straight, and the opposite margins are symmetrical.
Length of frond 1/92 of an inch; breadth 1/590.
Tab. XXXIV. fig. 4. a. frond with endochrome; b. empty frond.
6. P. truncatum (Bréb.); frond smooth, cylindrical with truncate ends; sporangia orbicular, easily detached from the conjugated fronds.
Dolgelley, J. R.
Falaise, Brébisson.
Frond very minute, two or three times longer than broad, smooth, cylindrical with truncate ends, sometimes slightly constricted at the middle. The endochrome is similar to that of Penium Brébissonii, but the transverse pale band at the middle is usually more distinct.
The empty frond is colourless, and its suture imperceptible. I believe that it is minutely dotted, but the dots are too indistinct to assist in defining the species.
I have gathered the sporangia rather abundantly in a pool near Dolgelley;
l53
they are orbicular and situated between the conjugating fronds, from which, after their formation, they soon become detached.
Penium truncatum closely resembles a small specimen of P. Brébissonii, but it is much smaller and its ends are truncate. In form it agrees with P. Cylindrus, but in that species the empty frond is coloured and distinctly granulate.
Length of frond from 1/969 to 1/555 of an inch; breadth from 1/2212 to 1/2100; diameter of sporangium 1/950.
Tab. XXV. fig. 5. a, b, c. mature fronds; d. dividing frond; e. conjugated fronds; f , g. sporangia.
7. P. Jenneri --- ; frond smooth, cylindrical with rounded ends; sporangium orbicular, situated between the conjugating fronds, which are deciduous.
Bogs at Fisher's Castle, Tunbridge Wells, Mr. Jenner.
Frond variable in length, from two to four times longer than broad, oblong or cylindrical with rounded ends.
I know no character by which to distinguish the usual state of Penium Jenneri from P. Brebissonii. They agree in size and form; In both the arrangement of the endochrome is similar, and the transverse pale band at the middle is often indistinct; the empty frond also is smooth and colourless, and no suture can be detected. Still the different forms of their sporangia compel us to consider them as distinct species.
In the present plant the conjugating fronds do not open and gape at the suture, as is usual in the Desmidieae, but couple by small and distinct cylindrical tubes, like many in the Conjugatae. The sporangium is orbicular and situated between the fronds, within the dilated connecting tube. The frond in Penium Jenneri is more rounded at its ends and larger than those of P. truncatum; in the latter species, moreover, the conjugating cells gape at the suture; in both they are but slightly attached to the sporangium.
Length of frond from 1/810 to 1/433 of an inch; breadth from 1/1724 to 1/1666; diameter of sporangium 1/1000.
Tab. XXXIII. fig. 2. a, b, c, e. fronds with endochrome; d. empty frond; f. dividing frond; g. conjugated fronds; h, i. mature sporangia.
††
8. P. Brebissonii (Menegh.); frond smooth, cylindrical with rounded ends, transverse central band inconspicuous; sporangium at first quadrate but finally orbicular; conjugating fronds persistent.
Palmella cylindrospora, Brébisson, Alg. Fal. p. 64 (1835).
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Very common, especially where water lodges in wet weather. Cornwall and Wales, J. R. Ayrshire, Rev. D. Landsborough. Aberdeenshire and Banffshire, Dr. Dickie and Mr. P. Grant. Northamptonshire, Rev. M. J. Berkeley. Sussex, Kent, Surrey, and near Southampton, Mr. Jenner. Ireland, Mr. Andrews. Essex, Mr. Hassall. Near Bristol, Mr. Thwaites and Mr. Broome. Westmoreland, Mr. Sidebotham. Rochdale, Mr. Coates.
Falaise, Brébisson. Germany, Kützing. Princeton, New Jersey, with sporangia, Bailey.
Frond minute, often congregated into a mucous stratum on wet mod, in the same manner as Tetmemorus granulatus, its frequent companion, which at first sight it resembles. The fronds vary much in size, from two to six times longer than broad, and are oblong or cylindrical with rounded ends. The transverse pale central band, which in the Desmidieae indicates the suture or junction of the segments, is less conspicuous here than in any other plant of the family. The endochrome being usually denser at the middle of each segment produces a resemblance to a joint of a species of Tyndaridea. The end view is circular with a central nucleus. The empty frond is smooth and colourless; no suture can be detected in it. The sporangia have been gathered by me at Dolgelley; by Mr. Jenner on Piltdown Common and near Tunbridge Wells, Sussex, and by Mr. Thwaites near Bristol. The process of conjugation in this species differs from that in the rest of this genus; for, as in Hyalotheca dissiliens, the conjugating cells enter into the formation of the containing cell and are permanently attached to the sporangium, instead of being at length detached, as commonly happens in the Desmidieae. The sporangium is at first cruciform, then quadrate, and finally orbicular.
Penium Brebissonii has been placed with the Palmelleae by Meneghini and Brébisson, because the division into two segments is but obscurely indicated, and its fronds often form a mucous stratum. I cannot however concur with them, and I consider that it has been correctly removed by Kützing to this family. Tetmemorus granulatus, Cosmarium curtum, and other undoubted Desmidieae, form similar strata, are often mingled with it, and by the naked eye cannot be distinguished from it. In its formation of sporangia this plant also agrees with the undoubted members of the family.
That this species has been referred to the Palmelleae by such distinguished algologists proves indeed how closely the families are allied. M. de Brébisson, in a recent letter, admits that it may belong to the Desmidieae, but considers that the difference in the formation of its sporangia is a sufficient reason for keeping the genus. Admitting that in strictness his view is correct, I nevertheless place this species in Penium, because the conjugated state, occurring so rarely, would seldom enable the student to distinguish between Penium and Cylindrocystis.
Length of frond from 1/637 to 1/404 of an inch; breadth from 1/1666 to 1/578; length of side of quadrate sporangium from 1/777 to 1/694; diameter of mature sporangium 1/470.
Tab. XXV. fig. 6. a, b. fronds with endochrome; c, d. empty fronds; e, f, g. imperfect sporangia; h, i. mature sporangia.
Cylindrocystis Brebissonii, Meneghini, Cenni sulla organografia e fisiol. delle Alg. pp. 5, 26 (1838); Monog. Nost. t. 12. f. 3. Hassall, Brit. Freshwater Alg. p. 361. t. 92. f. 17.
Cymbella ? laetevirens, Harvey, Man. of Brit. Alg. p. 216 (1841).
Closterium Cylindrocystis, Kützing, Phy. Germ. p. 132 (l845).
