The Macrocystis pyrifera and the Laminaria radiata are the most remarkable of marine plants, for their gigantic size and the extent of their range. They are met with on the antarctic coasts two degrees nearer the pole than any other vegetable, except the Diatomaceæ. The stem of the Macrocystis is slender, smooth, round, and slimy, rising from a fibrous root, like other Laminariæ, and bearing at its tip a lanceolate or oblong lanceolate frond. This frond divides at the base; the fissures extend upwards so as to form two petioles, each of which swells into an oblong or pyriform air-vessel. Another fissure is formed in a similar way a little above, and so on, till a single frond may at the same time have eight or ten fissures, each of which will ultimately gain the common apex. The margins of the fissures are at first perfectly smooth, but they soon become ciliated like the outer edge. The continuity with the fibrous base is at last broken, and the divisions of the leaves going on indefinitely, the whole reaches the length of some hundred feet, forming enormous floating masses which are wafted by the waves hundreds of miles from their origin. Fructification only takes place in young plants; consequently in such as are still attached to their native rocks. Even in that youthful state, Mr. Darwin mentions that such is the buoyancy of this powerful weed, that there is scarcely a loose block of stone on the coasts of Cape Horn that is not buoyed up by it.[47] The Macrocystis is native on the shores of the Atlantic, from Cape Horn to 43° S. latitude; but on the Pacific coast, according to Dr. Hooker, it extends to the river San Francisco in California, and perhaps to Kamschatka. The plant is reproduced by pyriform cells, full of endochrome, in nearly parallel rows imbedded in the fronds. The rocky coasts of the Falkland Islands are covered with a vast growth of the gigantic Macrocystis mixed with forests of the arborescent Lessonia, which forms large dichotomous trees with a stem from eight to ten feet high and a foot in diameter. The leaves are two or three feet long, drooping from the forked branches like weeping willows. In the Lessonia nigrescens the quadripartite endochrome, ultimately resolved into spores, is contained in thickened club-shaped cells springing vertically between the surfaces of the frond.