ALGAE SEA WEED OCEAN LIFE The Sea-weeds belong to the cellular order of vegetables, and to the Cryptogamic class of the Linnman system. The term Algm, is applied to a vast class of aquatic plants, many of which are inhabitants of fresh water. But the highest forms are those popularly termed Sea-weeds.
" The root among the Algm is rarely much developed. They do not, in a general way, derive nourishment from the soil on which they grow. We find them growing indifferently on rocks of various mineralogical character, on floating timber, on' shells, on iron, or other metal, on each other—in fine, on any substance which is long submerged, and which affords a foothold. Into none of those substances do they emit roots, nor do we find that they cause their decay, or appropriate to themselves the consti tuents of these substances. They are nourished by the water that surrounds them, and the various substances which are dis solved in it." " On whatever substance the Algm may feed, it is rarely ob tained through the intervention of a root. Dissolved in the water that bathes the whole frond, the food is imbibed equally through all the cells of the surface, and passes from cell to cell toward those parts that are more actively assimilating, or growing more rapidly. The root, when such an organ exists, is a mere hold fast, intended to keep the plant fixed to a base, and prevent its being driven about by the action of the waves. It is ordinarily a simple disc or conical expansion of the base of the stem, strongly applied and firmly adhering to the substance on which the A lgm grows. This is the usual form among all the smaller growing kinds. When, however, as in the gigantic Oar-weeds, the frond attains a large size, offering a proportionate resistance to the waves, the central disc is strengthened by lateral hold fasts or discs formed at the bases of side roots emitted by the lower part of the stem. The only instances of penetrating roots among the Algae, with which I am acquainted, occur in certain genera of Sophonew and in the Caulerpeee, tropical and sub-tro pical forms. But neither in these cases do the roots appear to differ from the nature of holdfasts, and their ramification and extension through the sand is probably owing to the unstable nature of such a soil. It is not in search of nourishment, but of stability, that the fibres of their roots are put forth, like so many tendrils." Three principal varieties of color are generally noticed among the Algae, namely : grass-green or herbaceous, olive-green, and red. In the sub-division of Algm into three groups, the color of the frond is employed as a convenient diagnostic character. The sea, in all explored latitudes, has a vegetation of Algae. To wards the poles this is restricted to microscopic kinds, but almost as soon as the coast rock ceases to be coated with ice, it begins to be clothed with Fuci. Climate has an effect on the Algee as upon all other organic bodies, though its influence is less percep tible in them than in the terrestrial plants, because the tempera ture of the sea is much less variable than that of the air. Still,
as the temperature of the ocean varies with the latitude, we find in the marine vegetation a corresponding change ; certain groups being confined to the colder regions of the sea, and others only vegetating where the mean temperature is considerable. The uses of the Algae may be considered under two points of view, namely : the general office which this great class of plants, as a class, discharges in the economy of nature ; and those minor use ful applications of separate species which man selects on dis covering that they can yield materials to supply his various wants. The part committed to the Algm in the household of nature, though humble when we regard them as the lowest organic members in that great family, is not only highly important to the general welfare of the organic world, but, indeed, indispens able. This we shall at once admit, when we reflect on the vast preponderance of the ocean over the land on the surface of the earth, and bear in mind that almost the whole submarine vegeta tion consists of It is one of the laws of nature, that animals shall feed on organized matter, and vegetables on unorganized. For the sup port of animal life, therefore, we require vegetables to change the mineral constituents of the surrounding media into suitable nutriment. In the sea this office of vegetation is almost exclu sively committed to the Algm, and we may judge of the complete ness with which they execute their mission by the fecundity of the animal world which depends upon them. Not that I would assert that all, or nearly all, the marine animals are directly dependent on the Algm for their food ; for the reverse is noto riously the case. But in every class we find species which derive the whole or a part of their nourishment from the Algm ; and there are myriads of the lower in organization which do depend upon them altogether. Among the higher orders of Algm feeders I may mention the Turtles, whose green fat, so prized by Alder manic palate, may possibly be colored by the unctuous green juices of the Caulerpm, on which they browse. But without further notice of those that directly depend on the Algm, it is manifest that all must ultimately, though indirectly, depend on whatever agency in the first instance seizes on inorganic matter, and converts it into living substance suitable to enter into the composition of animal nerve and muscle. And this agency is assuredly the office of the vegetable kingdom, here confined in the main to Algm ; proving that they are indispensable to the con tinuance of organic life in the sea. They also keep pure the water in which they vegetate, and yield a considerable portion of oxygen gas to the atmosphere.
The Algae have served as food both for man and cattle; and have been much employed in agriculture and the arts. But they have proved most valuable to man, in affording substances which prove highly beneficial in the treatment of disease.