a. With a single longitudinal nerve, simple or branched. —This includes several beautiful species, common on all our shores, F. sanguineus, sinuosus, alatus and dentatus ; with F. ruscifolius, (Turn. t. 15.) found on the south coast of England. Speaking of the first of these, F. sanguineus, Mr. Turner remarks, that " in the elegance of its appear ance, and the exquisite colour of its must delicately veined leaves, this plant so much excels all its congeners, that it carries away the palm with no less justice from the vegetables of the ocean, than the rose, the flower of the poets, from its rivals in the garden." b. With the longitudinal nerves buried in the substance of the leaves. This takes in F. rube ns and laceratus, found on our shores. The former is admirably described and figured by Lightfoot, in the Flora Scolica, vol. ii. p. 949. t. 30. under the title of F. proffer. The latter is one cf the variable foci, Mr Turner (Hist. Fuc. t. 68.) describing no fewer than eight varieties. It is F. endivixfolius of the Flora Scotica, t. 32. and it is to be observed that the longi tudinal veins, not being readily perceived, have been over looked by Lightfoot and others.
c. Without any nerve or midrib. This includes the well-known F. palmatus. or dilse of Scotland, with the re markably variable F. ciliatus, (Turn. t. 70.) which is alsa eaten ; as well as F. edulis, (t. 114.) which, as implied in Ore trivial name, is considered as fit for food. F. Brodixi of Turner, t. 72. likewise falls under this section : this spe cies was found on the shores of Nairnshire, by Mr Brodie of Brodie, who likewise detected its fructification, and as certained the specific differences of the plant.
S Chondrus. "Tubercles hemispherical or oval, situa ted on the surface of the leaves, never on the edges nor the extremities ; leaves flat, branched, sometimes mamillary." —The generic name, it will be observed, is adopted from Stackhouse ; but the character is changed. The small black lichen-like fucus, F. Onus, which covers many of our sandstone and greenstone rocks at high-water mark, belongs to this genus.
4. Gelidium : "Tubercles nearly opake, oblong, situated on the branches or at their extremities." The generic name is derived from the quality which the plants possess, of being almost entirely reduced to a gelatinous substance, by boiling or maceration. The foreign species, of which the swallows in India construct the edible nests, Lamou roux considers as belonging to this genus. F. corneus (Stackh.p. 61. t. 12.) and F. coronopifolius (Turn. t. 122) rarely found on the English coast, rre likewise gelidia.
5. Laurencia: " Tubercles globular, somewhat like grape-stones, situated at the extremities of the branches and their divisions." F. pinnatifidus, the pepper-dilse of Scotland, may be mentioned as an example.
6. Hy/inea: "Tubercles subulated, almost opake." This is named from its general resemblance to the branched mosses or hypnums ; but the fructification is not readily seen without a lens. F. Wigghii, (Turn. t. 102.) belongs to this genus. All the species arc annuals.
7. Acanthophora : " Tubercles roundish, and spiny." The species of this genus arc equatorial plants, in general appearance resembling Hypnex.
8. Dumontia : " Capsules solitary, scattered, innate in the substance of the plant ; stem and branches fistular." The species are all of very delicate structure, and annuals.
9. Gigartina : "Tubercles spherical or hemispherical, sessile, like grape-stones, filled with a semitransparent mucilaginous substance ; stem uniformly cylindrical."— This includes most of the genus Ceramium of Roth. It is divided into three sections.
a. With distinct leaves ; as F. subfuscus (Turn. t. 10.) and tenuissfmus, (t. 100.) not uncommon on our shores.
b. Without leaves ; stem and branches without contrac tions ; as F. confervoides, (Turn. t. 84.) purpurascens (t. 9.) and plicatus (t. 130.) of our shores.
c. With evident contractions, as F. kaliformis, ( Turn. t. 29.), articulates (t. 106.), and opuntia (t. 107.) of the Bri tish shores.
10. P/ocaudum " Tubercles somewhat like grape stones ; stems and branches compressed, the extremities partitioned, or divided by septa."—The plants of this genus approach nearest to the truly articulated sea-weeds or ma rine confervce. They are all annual ; and many of them parasitical on the perennial species. The elegant F. plu mosus of our shores belongs to this genus ; and the disse piments in the extreme branches, or pinn2e, are beautiful ly delineated by Mr Turner, (Hist. Fuc. t. 60.) It must, however, be remarked, that though this new genus is evi dently named from F. plocamium of Gmelin (F. coccineus of Hudson and others) ; yet this species, instead of afford ing a characteristic example of the genus, exhibits no traces of dissepirnems in its branchlets.
11. Champia: " Capsules numerous, somewhat egg shaped ; situated in papilla rising ft om the stem and branches."—This consists only of one species, a native of the shores of the Cape of Good Hope.
The third order, DICTYOTE.E, is distinguished by the being reticulated and foliaceous; the colour greenish, and not liable to bccotne black on exposu1e to the air." This family consists of four genera, Amansia, Dictyopteris, Dictyota, and Flabellaria, all of them well characterized by the reticulated organization, which is vi sible with a common lens, or even by the naked eye. The fructifications are numerous, covering the surface of the leaves, on which they occur in groups of various shapes. The root consists of a fibrous callosity, furnished with very fine long whitish hairs, which become yellowish or brown in drying. In some species these hairs extend up the stem, or are continued on one side of the frond. They in crease in number with the age of the plant. They seem analagous to the tufts observable on F. serratus, vesieu losus, and natans, and are probably secreting and absorbing organs. The dictyotex, which have nerves or midribs, are perennial, and are found chiefly in equatorial latitudes: those destitute of nerves are annual, and found chiefly in the northern seas.