containing two roundish masses; sporidia sub-globose, lodged in one of the filaments. Harv. l. c. p. 361. Zygnema cruciatum, gracile and decussatum, Ag. Conf. bipunctata, Dillw. t. 2, and C. decussata, Syn. p. 51.

In ditches and pools, common. This forms extensive masses of a yellow-green colour, finally rising to the surface. The articulations vary in length, and are marked by two roundish starry masses.

2. T. pectinata, Harv. ; joints shorter than their diameter, containing two linear, transverse masses; sporidia contained in the swollen, transverse tubes. Harv. l. c. p. 361. Conf. bipunctata, E. Bot. t. 1610. C. bipartita, E. Bot. t. 2302?

In stagnant water, common." This, like T. cruciata, occurs in large, yellowish, floating masses. They are often found intermixed, nor is there anything to distinguish them from each other in their usual state, but the transversely oblong shape of the internal dots, which results probably from the shortness of the articulations. In a state of junction, however, the position of the sporidia leaves no doubt that they are distinct species." Carm.

3. T. epigaa, Harv.; "filaments interwoven into a crisped stratum; articulations once and a half as long as broad; granular mass dense, scarcely bipartite; sporidia globose, lodged in one of the filaments." Carm.-Harv. l. c. p. 361. Zygnema epigæum, Carm. Alg. App. ined.

On road-sides and frequented paths. Spring to autumn. Appin, Capt. Carmichael. "Filaments an inch or more in length, as thick as those of T. cruciata, spreading to an indefinite extent in a thin, intricate, yellowish fleece over the dry, naked earth; here and there grouped and curled in a most characteristic manner. Articulations 1--3 times longer than broad, and remarkably opaque; internal mass partially separating into two square smooth portions. Sporidia sphærical, lodged in one of the filaments." Carm.

4. T.? bicolor, Harv.; "filaments simple, slender, straight, bright green; joints thrice as long as broad, white-edged, even, several of them together here and there empty, white and pellucid." Sm.-Conf. bicolor, E. Bot. t. 2288.

On stones in a rapid streamlet at Henfield, Sussex, Mr. Borrer. not acquainted with this plant.

LXXIII. ZYGNEMA. Ag.

I am

Filaments articulated, simple, finally united in pairs by numerous transverse tubes. Endochrome consisting of granules arranged in spiral rings or in a simple row, which, after conjugation, are condensed into a globule in one of the filaments, or in the transverse tubes.-Name, ʊyos, a yoke, and mua, a thread; the threads, which are at first separate, being afterwards yoked together.

1. Z. nitidum, Ag. ; filaments dark green, parallelly joined; articulations containing numerous, arched spires of granules Harv. l. c. p. 362. Conf. nitida, Dillw. t. 4, f. C, (bad).

In ditches &c. frequent. Filaments dark green, very lubricous, as thick as horse-hair, rigid, forming large masses. Articulations usually a little longer than broad, but Capt. Carmichael sometimes found them six times as long as their diameter. After conjugation the filaments, in this and the following species, become crisp, fragile, and lose much of their lubricity; the spires are soon after deranged and the contents of one articulation discharged through its tube into the opposite one, where they form a dark-coloured globule.

2. Z. deciminum, Ag.; filaments dark green, parallelly joined; spires two, crossing each other. Harv. l. c. p. 362. Conf. jugalis, Dillw. t. 5, and C. nitida, t. 4, ƒ. A, B.

In ditches &c. very common.-Forming large, glossy and slippery strata resembling the preceding. Filaments more slender, but varying much in this respect and in the length of the joints, on which characters but little dependance can be placed. Z. elongatum, Berk. Alg. t. 12, f. 2, represents one of these varieties. The spires are constantly double, crossing each other, like a continual series of the Roman numeral X, whence the specific name; in the long-jointed varieties they are very lax; in the short-jointed dense.

3. Z. quininum, Ag.; filaments pale yellow-green, parallelly joined; spires simple. Harv. l. c. p. 362. Conf. spiralis, Dillw. t. 3.

In ditches and pools, very common; forming pale, cloudy, yellow-green masses.-Filaments glossy, varying much in diameter and in the length of the joints, marked with a spiral line resembling a continual series of the Roman numeral V.

4. Z. curvatum, Ag.; "filaments green, unbranched, very slender, here and there slightly bent and combined by their angles; joints cylindrical, four times as long as broad; colouring matter in a triple, irregular series of dots." Sm.Harv. l. c. p. 362. Conf. stictica, E. Bot. t. 2463.

Ditches in Henfield level, Sussex; and pools on Chy-an-Hâl Moor, near Penzance, Mr. Borrer. This species seems to be intermediate between the genera Zygnema and Mougeotia. "When young, the colour is a dull pale green, and about three imperfectly spiral lines of granules are with difficulty distinguishable: afterwards these lines become more conspicuous, the rest of the filaments being now perfectly colourless, and their component granules larger, but their arrangement is still irregular. The threads subsequently unite here and there, not by every joint, and their connecting processes are usually nearer to one end of the joints than to the other. Such filaments are divaricated at the points of connection, rather less abruptly than in M. genuflexa. In some of the combined joints, the contents appear unchanged, in others they form a mass of larger granules than in the lines; and some have a large oval seed, which often swells the joints. Traces of unchanged lines occur, now and then, in the fructifying joints." Eng. Bot.

144

ZYGNEMA-SPHÆROPLEA-APHANIZOMENON.

5. Z. ordinarium, Berk.; "articulations 4-6 times as long as broad, filled with sporaceous matter, through the centre of which runs a single series of granules; seeds globose, in the transverse tubes." Berk. Gl. Alg. t. 12, f. 1.

In ditches and pools, rare. Glapthorn, Northamptonshire, Rev. M. J. Berkeley.-Forming green masses floating freely in the water.

LXXIV. SPHÆROPLEA. Ag.

Threads at first articulated, at length filled with sporaceous globes which move freely in them. Berk.-Name, opaiça, a globe, and λ05, full; full of globes.

1. S. crispa, Berk.; "threads erect, short, green, mucous, crisp, simple, at first with articulations as broad as long, filled with minute, distinct granules, then with parallel rings, which at length become globular, and escape in moniliform threads." Berk. Gl. Alg. t. 3, f. 1.

Growing on stones, aquatic plants &c., in early spring, not uncommon ; Rev. M. J. Berkeley-Tufts half an inch to an inch in length, deep green. "Filaments at first of a uniform green, either dotted without any appearance of joints, or divided by dark lines into articulations scarcely so long as broad, which contain a few granules larger than the rest. A few threads have them scarcely broader than in some Oscillatoriæ, but as these are colourless, they are probably abortive. The sporaceous mass at length assumes the form of annular disks, which are sometimes dark, sometimes light in the centre, and the articulations are invisible. This is the most usual appearance; but occasionally the ring is formed in the centre of the joint, and there becomes globular without any rupture or absorption of the dissepiment. In general the globules float freely in the tube, and at length escape in moniliform filaments." Berk.

2. S. punctalis, Berk.; "floating, pale green; threads very slender, mucous, flexuous; articulations about as broad as long, containing a dotted, sporaceous mass." Berk. Gl. Alg. t. 3, f. 2. Conf. punctalis, Dillw. t. 51.

Floating on the surface of fresh-water pools, Rev. M. J. Berkeley.-Forming crisped masses of a light green colour. Filaments very slender, mucous, flexuons. Articulations as long as broad, at first containing a square, at length a globular coloured mass.

LXXV. APHANIZOMENON. Morren.

Filaments simple, cylindrical, flexile, membranaceous, glassy, articulated; cohering together in flat laminæ, laciniated at the apex, straight, or here and there inflated, full of green matter, oscillating, spontaneously falling to pieces. Mor.-Name, apavtoμevov, a vanishing thing.

1. A. incurvum, Morren. Mem. cum. icone.

In lakes and ditches, floating on the surface. Ballydrain Lake, near Belfast, Mr. W. Thompson. "Lamella flat, light green, incurved, composed of united threads; articulations 2-8 times longer than broad, discrete, bluish green.” Morren.--For a more detailed account of this curious little plant, I must refer to Dr. Morren's Memoir read before the Royal Academy of Brussels in December, 1837; published, I believe, in their Transactions, but to be had in a separate form. Mr. Thompson's specimens were seen by Dr. Morren.

TRIBE 18. SIPHONEÆ.

LXXVI. CODIUM. Stackh.

Frond spongy, dark green, (crustaceous, globular, cylindrical or flat), composed of an interwoven mass of tubular, continuous filaments. Fructification: opaque vesicles attached to the filaments, near the surface of the frond. Grev. -Name, zodiov, the skin of an animal; from the soft substance.

1. C. tomentosum, Stackh.; frond cylindrical, dichotomous. Grev. Alg. Brit. p. 185, t. 19; Hook. Br. Fl. ii. p. 318; Wyatt, Alg. Danm. No. 35. Fucus tomentosus, E. Bot. t. 712.

On rocks in the sea; frequent. Perennial. Summer. Frond rising from a spreading spongy base, cylindrical, from a quarter to nearly half an inch in diameter, 6-12 inches long, more or less regularly divided in a dichotomous manner; sometimes regularly dichotomous; sometimes palmato-partite, the segments forked; sometimes beset with short lateral branches. Structure filamentous, the centre composed of longitudinal, interlaced, colourless fibres, the circumference of radiating, horizontal, clubshaped, deep green filaments, invested by a viscid gelatine. Fructification : dark green ovate vesicles, borne by the club-shaped filaments.

2. C. Bursa, Ag.; frond sphærical, hollow. Grev. Alg. Brit. p. 186; Hook. Br. Fl. ii. p. 318. Fucus Bursa, E. Bot. t. 2183.

On rocks in the sea, very rare. Perennial? Summer. "Coast of Sussex, plentifully, Pallas; » Turner. Shores of Cornwall, Mr. Rashleigh. Near Torquay, Mrs. Griffiths. Belfast, Mr. Templeton.-Frond a globular, spongy, hollow ball, 1-8 inches in diameter. Structure similar to the preceding.

3. C. adhærens, Ag.; frond forming a velvetty crust on the surface of rocks. Harv. in Hook. Journ. Bot. p. 305; Wyatt, Alg. Danm. No. 127.

On rocks in the sea, near low-water mark; very rare. Annual? At Torquay, Mrs. Griffiths. - Spreading over the rock in irregular patches of two feet or more in extent, resembling "fragments of beautiful green velvet." Substance gelatinous, dense, closely adhering to paper. Mrs. Griffiths, who has watched this plant from its first appearance till it had

L

considerably extended itself, remarks "that it does not show the least tendency to throw up a frond. It has an uneven surface from taking the form of the rock, or even roots of coarse weeds, over which it crosses." She considers it a true species.

LXXVII. BRYOPSIS. Lamour.

Frond membranaceous, filiform, tubular, cylindrical, glistening, branched; the branches imbricated, or distichous and pinnated, filled with a fine green, minutely granuliferous fluid. Grev.-Name, Bpvov, a moss, and wis, an appearance.

1. B. plumosa, Ag.; frond filiform, branched, naked below, the branches scattered, spreading, twice or thrice pinnated, the pinnæ pectinated. Grev. Alg. Brit. p. 187, t. 19; Hook. Br. Fl. ii. p. 318; Wyatt, Alg. Dunm. No. 128. Ulva plumosa, E. Bot. t. 2375.

On rocks &c. in the sea. Annual. Summer and autumn.--Frond 1-4 inches high, more or less branched, sometimes with a nearly simple stem, set with numerous close branches; at other times much divided in a subdichotomous or irregular manner. Branches naked at base, in the upper part closely pinnated with subopposite, slender, distichous or rarely irregular ramuli, which gradually diminish in length to the apex. Colour a fine deep green. Substance lubricous and adhering to paper. plant, whose branches resemble beautiful, glossy, bright green feathers.

A beautiful

2. B. hypnoides, Lamour.; frond slender, very much branched; the branches long; the ramuli capillary, irregularly inserted, somewhat erect, the lower ones elongated. Grev.-Hook. Br. Fl. ii. p. 318; Wyatt, Alg. Danm. No. 81.

On rocks and stones in the sea, rare. Southerness, Kirkcudbright, Sir W. Jardine, Bart. Frith of Forth, Dr. Hasell. Appin, Capt. Carmichael. Torquay, Mrs. Griffiths. Portrush, North of Ireland, Mr. D. Moore.— Frond 2-4 inches high, much branched, the branches repeatedly divided in an alternate or irregular manner; lesser branches set with irregularly scattered, somewhat pinnate, more or less dense ramuli. Colour a fine yellow green. This is a more slender, very much more branched plant than the preceding, and the ramuli are irregularly scattered, sometimes issuing from all sides of the filaments.

LXXVIII. VAUCHERIA. De Cand.

Fronds aggregated, tubular, continuous, capillary, coloured by an internal, green, pulverulent mass. Fructification: dark green, homogeneous vesicles (coniocystæ), attached to the frond. Grev.-Named in honour of M. Vaucher, a distinguished writer on fresh-water Conferva.