1. Aniansia: " Reticulations hexagonal, regular and elongated, with the points acute."—The species are fo reign.
2. Dietyoptcris: " Capsules forming masses slightly elevated ; scattered over the leaves, which are divided by a single nerve." All the species are natives of warm cli mates.
3. Dietyota: " Capsules collected in masses, forming lines having various directions."—This is divided into two sections: a. Fortino, with the fructification in transverse, incurvated, and coneeLtrie lines : b. Dictyota proper, with the fructification in longitudinal lines, rarely transverse and never concentric, often entirely or partially scattered. The padina are analogous to the fuci corallini of Gmeliu, and include those species which the late M. Draparnaud proposed to associate as a genus, under the title of Zo naria.
4. Flabellaria : " Fructification unknown; reticulations very fine it.n1 intermixed, so as to produce an appearance of felt."—This includes only one species, found in the Me diterranean.
The fourth order, Unynenx, is distinguished by the " organization being herbaceous and uniform, the colour green, becoming yellowish or whitish in drying.''—This order comprises four genera, Asperocoecus, Ulva, Bryop sis, and Caulerpa. It includes most of the species of the genus Ulva of Limmus and others. The organization re sembles that of the seminal leaves of many land plants, a herbaceous tissue, destitute of fibres and vessels. The plants of this order abound with a mucilaginous matter, in which the colouring principle resides. The nature of the fructification is not yet accurately known. It is apparent ly very simple, seeming to consist of naked seeds imbed ded in the frond at its surface. The bodies which liav . been taken for seeds, however, may in reality prove to be capsules, containing granules or seeds.
1. Asperococcus : " Seeds solitary, scattered, at first in- nate, but afterwards prominent ; stems this genus, Ulva rugosa, Lin. may be considered as an example.
2. Ulva : " Seeds solitary, innate in the substance. of the plant, scattered, never prominent."—This genus is divided into two sections: a. With flat leaves ; as U. lactuca, latissima, all very common on our shores.
b. With fistular leaves ; as U. compressa, which covers with its fine green colour almost all rocks where brackish water occurs.
3. Bryopsis : " Seeds globular, green, contained in the stem, or the branches, which are always fistular."—All the species are foreign.
4. Caulerpa : cc Fructification unknown ; stem cylindri cal, horizontal, creeping, and branched."—This is a curi ous genus, first described and figured in the French Annals of Botany for by M. Lamouroux. It is not clearly ascertained whether some, or perhaps e all the species, should not rather be considered as belonging to the animal than to the vegetable kingdom. The organization certainly
differs from that of marine plants in general, and is more ana logous to that of some zoophytes. Weber and Mohr right ly remark, that the stiff straw-coloured stem of a caulerpa exhibits few traces of vegetable organization. Even with the aid of a microscope, neither fibres nor reticulations can be detected ; an epidermis is observable, and a cellular tis sue, the cells of which are so extremely minute, that it is impossible to determine their form. The caulerpze are des titute of any gelatinous or viscid property. Their mem branaceous substance, and their uniformly green colour, have induced Lamouroux to place them among the Ulva cex. Sometimes the leaves of a particular species, Can lerpa prolifera, are partly covered with small opake points ; such leaves have not the brilliancy nor half the transparen cy of the others ; they are of a dull earthy green colour. If these points prove to be seed-vessels, then is Caulerpa properly placed among the Ulvacex ; but the fructification is at present completely unknown. The roots are entirely fibrous, like those of many of the flexible zoophytes. The Caulerpx grow, not on rocks, but on sandy shores, gene rally near high water mark, creeping in the loose sand and sail ; and no other sea-weeds possess a similar mode of at tachment. Viewed as plants, they may be considered (as formerly stated) as connecting sea-weeds with the vegeta bles of the earth. All tile species are foreign, most of them tropical. When fresh, they are of a line grass-green co lour, which is liable to pass to a transparent horny white. Several of them are figured by Turner, under the names of F. pinnatus, taxifolius, clavifer, (Hist. Atte. t. 53,5.1,57)V and lie has added some, entirely unknown to Lamouroux. Among these may be mentioned, F. cactoides, (t. 171.) brought by Mr Brown from the south coast of New !Tol land ; and F. hypnoides, (t. 173.) brought from Kent's Islands by the same naturalist. This last is not only sin gular for its beauty, but is very remarkable for the exte rior of the stem being closely beset with small scales, like some of the fern tribe : to this there is nothing analogous among the rest of the foci ; the scales in F. squamulosus (Turn. t. 128.) being occasioned merely by the remains of old ramuli. The other new species of Cau lerpa published by 'Fume') were brought from the Red Sea by Mr Salt, and are likewise very curious. The Caulerpa appear to be perennials, or at least to endure for more than one year. We may remark, that the sea-weed of a fine green colour, described by Humboldt as found growing in the sea at the great depth of 192 feet, and by him named Fucus vitifolius, belongs to this genus.