Page:Evolution of Life (Henry Cadwalader Chapman, 1873).djvu/113

Rh from which the group takes 'its name, is the green plant which usually adorns marine aquaria. It is composed of layers of cells bound together, and its reproduction is effected by zoospores, such as we noticed in Pediastrum.

The brown or olive-colored Algae, or Fucoidae, differ not only in their color from the green Algae, of which we have just spoken, but equally as regards their size and manner of reproduction. They are confined to the sea, and are found generally on submarine rocks, which are exposed, however, at low tide, to heat, light, and atmospheric influences. This seems to be necessary for the healthy growth of the brown Algae, since the specimens that are brought up from greater depths do not exhibit so hardy a structure as those that live at the surface. The Fucoidae are commonly known as sea-wrack; but that generally picked up at the sea-shore gives no idea of the immense size which some of the brown Algae attain, the Macrocystis of the Californian coasts reaching a length of four hundred feet. Among the Fucoidae are included the Laminaria, or leathery sea-weed; the Fucus (Fig. 99), or bladder-wrack, so called from floating on the surface of the sea by means of air-bladders. This bladder-like arrangement in the Sargassum, or gulf-weed, takes the form of a bunch of berries, and is the most characteristic feature of the plant. The importance of the brown Algae may be estimated from the fact that forty thousand square miles of the Atlantic Ocean are covered with a kind of oceanic forest of Sargassum. (Fig. 100.) The presence of this plant gave Columbus vain hopes of being near land. The reproduction of the brown Algae has not as yet been perfectly made out. It is known, however, that the process is sometimes carried on by zoospores, as in Pediastrum, or by the intervention