named are consequently indicators of a cold, the last of a sultry clime.

(310.) Besides the general features characteristic of these great zones, which have been made out satisfactorily in their main points by Lamouroux, Bory St. Vincent has endeavoured to trace the differences of marine vegetation in subordinate oceanic regions, similar to the geographical regions of terrestrial plants.

For not only does "the polar atlantic basin to the fortieth degree of north latitude present a well marked vegetation, but the same may be said of the West Indian sea, including the Gulf of Mexico, of the eastern coast of South America, of the Indian ocean and its gulfs, and of the shores of New Holland and the neighbouring islands. The Mediterranean possesses a vegetation peculiar to itself, extending as far as the Black Sea; and, notwithstanding the geographical proximity of the port of Alexandria and the coasts of Syria to those of Suez and the Red Sea, the marine plants of the former, in regard to species, differ almost entirely from those of the latter. Bory St. Vincent characterizes each of his Mediterranean seas by a vegetation different from that of the Arctic, Atlantic, Antarctic, Indian and Pacific Oceans; and to a certain extent, (says Greville,) he is probably correct, as such seas are of less depth, often of a higher temperature, and more directly influenced by the countries which more or less surround them. The seas which he considers Mediterranean are, besides the Mediterranean commonly so called, the Baltic Sea, the Red Sea, the Persian Gulf, the Chinese Sea, the seas of Ochotsk and Behring, and the West Indian Sea, along with the Gulf of Mexico, denominated by him the Columbian Mediterranean."

(311.) The topographical range of the several groups of the Fucales has been already in part given when treating of the individual types and sections; little, therefore, on this point, now remains to be done, but to generalize the distribution of the large groups; the smaller types do not afford sufficient materials for generalization.

(312.) Lamouroux states it as his belief, that about 1600 species of Fucales are known, and have been collected and preserved in herbaria; he further calculates, though not on unexceptionable data, that between 5000 and 6000 exist in the various regions he points out. Our present knowledge of these plants must be, therefore, if his calculations approach the truth, very rudimentary and imperfect, for not many more than 500 species have as yet been fully described and absolutely determined to belong to the order. [§ 294.]

These have been associated to form three sections and fifteen types.

(313.) Greville observes, in his Algologia, when treating on this

subject, that "it is very clear and well known to the practical botanist, that marine plants are much influenced by the nature of the soil, not merely in regard to species, but in luxuriance and rapidity of development. A few yards is, in some instances, sufficient to create a change; and the space of three or four miles, a very striking one. Thus, calcareous rock favors the production of some species; sandstone and basalt that of others; and it would appear that soil has an effect even upon those algae which grow parasitically upon larger species. But, sometimes, to all appearance independent of this cause, peculiar forms predominate in certain localities, both in regard to genera and species, which, as we approach their boundaries, gradually disappear, and often give place to others equally characteristic."

(314.) The very confined range of such plants gives the account of their distribution, a topographical, rather than a geographical, aspect. Others, however, though more widely spread, have been shewn to affect peculiar regions, and only to abound in certain latitudes; while others, again, are scattered over every part of the world.

(315.) "Amongst the Siphonacea, Codium tomentosum is found in the Atlantic, from the shores of England and Scotland to the Cape of Good Hope; in the Pacific, from Nootka Sound to the southern coast of New Holland. It abounds also in the Mediterranean, on the shores of France, Spain, and Africa, and is common in the Adriatic. It has, likewise, been recently brought from the coasts of Chili and Peru. This plant, however, is not a social one; it grows even in the same locality, in a solitary and scattered manner. The Ulvacea, on the contrary, are strictly social, and preserve this character in every part of the world. They appear, however, to attain to greatest perfection in the polar and temperate zones, although very fine Porphyræ have been brought from the Cape of Good Hope; and that they are capable of sustaining severe cold is proved by the fact, that fine specimens of Enteromorpha compressa, [§ 241], were picked up in high latitudes by some of the gentlemen who accompanied Captain Parry in his second voyage of discovery."-Greville.

(316.) Of the Lemaniaceæ, Furcellaceæ, Chordariaceæ, Lichinaceae, Spongiocarpaceae, Gastrocarpacea, Caulerpaceæ, and Thaumasiaceæ, several of which types consist of single genera, it may suffice to repeat that Lemania is the only fresh-water genus known; it inhabits mountain-torrents and impetuous streams in

the temperate regions both of Europe and North America. The Gastrocarpaces are indigenous to the temperate zone; Furcellaria, Chordaria, and Lichina, are also found upon our shores; and the Spongiocarpaceæ, both in the British seas and in those of Chili and New Holland. Caulerpa is confined to the southern hemisphere; and the extraordinary Thaumasia is a native of Ceylon.

It is evident, even from this brief recapitulation, that some of these plants have an extensive range, and that others, as far as we know, are extremely local; but, at present, too little information has been obtained to allow of further generalization.

(317.) The small groups being thus summarily disposed of, the four extensive types, Floracea, Dictyotacea, Laminacea, and Fucacea, are the only other ones remaining: and of their distribution, which is the most important, much more is known.

(318.) The Dictyotacea are rather tropical than European plants; for, although eight are found on the Scottish, and thirteen species on the English shores, they gradually and greatly increase, both in quantity and variety, in the seas nearer the equator.

(319.) The numerous genera and species of the very large type Floracea, are chiefly predominant in the north and south temperate zones. There are, however, various exceptions to this general rule. Hypnea and Acanthophora approach the type to the equatorial regions; and Amansia is exclusively found within the tropics. (320.) "The Laminacea, among which are the giants of the marine flora, exhibit, in a broad view, a tolerably decided geographical distribution. The Laminaria predominate from the fortieth to the sixty-fifth degree of latitude; while the Macrocystes seem, as far as we know, to exist from the equator to about the forty-fifth degree of south latitude."

(321.) The Fucaceae, and particularly the Fuci, are the especial sea-weeds of the temperate zones; being found in those latitudes, both in the northern and southern hemispheres, although they are absent from the intermediate equatorial regions. The Sargassum, or tropic grape, which has been already mentioned as being so abundant between the twenty-fifth and thirty-sixth degree of north latitude, may seem a serious objection to the above statement; but the Sargassa, although produced within the tropics, grow, there is little doubt, at very considerable depths, so that the temperature of their habitats is less than that of the surface of the ocean in the equatorial zone.

"In the genus Sargassum there is also observed a small group as local, and almost as peculiar, as that just mentioned of the Cystoseiræ. It occurs in the seas of China and Japan, and consists of Sargassum fulvellum, microceratium, macrocarpum, sisymbriöides, Horneri, pallidum, and hemiphyllum, distinguished from the rest by their terminal fructification, a slender habit, small nerveless leaves, and often elongated vesicles."-Grev.

GEOLOGICAL DISTRIBUTION OF THE FUCALES.

(322.) The chief difference observable in the geographical distribution of the two preceding orders is, that the Confervales are peculiarly the inhabitants of cold and temperate regions, very few being found either in warm springs or in the equatorial zone; while the Fucales are the most abundant within the tropics, and extend from the equator to the poles. Does the geological distribution of these latter plants confirm the general views which have been taken of the geographical range of the present existing species in as striking a manner as it has been found to do with respect to the Confervales? [$219, et seq.] Do the facts presented by one of these twin-branches of natural science strengthen or refute the conclusions arrived at by the other?

(323.) As was the case with the Confervales, the whole of the fossil inarticulated algæ are included in a single group, or genus; of which, according to Brongniart, the following are further distinctive characters: "Continuous fronds, usually irregular, neither symmetrical, nor subcylindrical; sometimes simple, but more frequently branched, occasionally naked, but more often leafy; either membranous, entire, or more or less lobed, with no ribs, or imperfectly marked ones, the markings being irregular, and never anastomosing.

(324.) Although Brongniart associates all the fossil remains of the Fuci in a single genus, which he calls Fucöides, he has subdivided the group into several sections, or subgenera, which will probably hereafter be esteemed genera, and the present genus a fossil order. These subgenera are known by the termination ites, instead of öides, being suffixed to the name of the modern genus, to which they seem severally to be most nearly allied. Thus Fucoides septentrionalis is called Sargassites; Fucoides strictus, Fucites; Fucoides tuberculosus, Laminarites; and so on of the rest.

(325.) Among the fossil remains of ancient plants which, from their resemblance to the Fucales, have been named Fucoides, about six and thirty species have been discovered, and satisfactorily determined to belong to the present order.

A. Fucoides encœliöides.

E. Ditto, apex of frond magnified. B. Fucoides serra. c. Fucoides Agardhianus. D. Fucoides Bertrandi. F. Ditto, portion magnified.

Of these, four species occur in the transition rocks, seven in the bituminous strata, three in the oolitic series, eleven in the chalk, and as many in the London clay formation. Thus, instead of being confined, like the Confervales, to the upper deposits of the secondary and tertiary groups, the Fucales are found in some of the most ancient strata of our globe. Geographically ranging through every latitude; geologically spread through almost every epoch; unmindful of temperature now, they seem to have been able, in like manner formerly, to endure heats, which their weaker brethren, the Confervæ, could not withstand.

(326.) The fossil species found in the transition rocks are, 1st. the F. antiquus, discovered in the neighbourhood of Christiana.

See Brongniart's History of Fossil Vegetables, page 412, et seq.; and Lindley and Hutton's Fossil Flora of Great Britain, Part iv.

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