The Sargassum bacciferum is often found in the Mediterranean, but only as a wanderer drifted in from the Atlantic, where masses of it, like floating meadows, occupy an area west of the Azores equal in extent to that of France, which has never changed its position since the time of Columbus, on account of the surrounding currents. Fields of it cover the seas near the Bahama Islands, and another permanent area of Sargassum of great extent occurs in the South Pacific. The Sargassum bacciferum is of a pale translucent olive colour, having branched stems, with lanceolate, midribbed, and serrated leaves, destitute of pores, and little stalked air-balls in the axils of the branches. The same individual continually produces new branches and leaves, and thus multiplies its species, but it never produces fruit; consequently its habits exactly resemble those of the Macrocystis, and as that plant becomes detached and floats after fructification, it is supposed that the Sargassum bacciferum may grow on rocks at the bottom of the Atlantic, between the parallels of forty degrees north and south of the equator, and when detached after fructification that it is uniformly drifted to particular spots which never vary. ‘Multiplication is so rapid in the floating beds of the Sargassum and Macrocystis, as to render fruit needless; and even the common Fucus vesiculosus occurs in the Mediterranean under a peculiar form consisting entirely of specimens derived from sea borne weed carried in by the current which sets in towards the Mediterranean from the Atlantic.’[51] Kelp, the ashes of sea weeds, is the commercial source of iodine. Algæ growing in deep water contain most of that substance; consequently the kelp made at Guernsey, consisting chiefly of the ashes of Laminaria digitata, is richer in iodine than that made elsewhere.