A few days' sail brought us into the "Gulf stream," the influence of which is felt as high as the 43° north latitude. We saw a considerable quantity of _fucus natans_, or gulf weed, but it generally was so far from the vessel, that I could not contrive to procure a sprig. Mr. Luccock, in his Notes on Brazil, says, that "if a nodule of this weed, taken fresh from the water at night, is hung up in a small cabin, it emits phosphorescent light enough to render objects visible." He describes the leaves of this plant as springing from the joints of the branches, oblong, indented at the edges, about an inch and a half long, and a quarter of an inch broad. Humboldt's description is somewhat different: he calls it the "vine-leaved fucus;" says, "the leaves are circular, of a _tender_ green, and indented at the edges, stem brown, and three inches long."--What I saw of this weed rather agrees with that described by Humboldt--the leaves were shaped like the vine leaf, and of a rusty-green colour. That portion of the Atlantic between the 22d and 34th parallels of latitude, and 26th and 58th meridians of longitude, is generally covered with fuci, and is termed by the Portuguese, _mar do sargasso_, or grassy sea. It was supposed by many, from the large quantities of this weed seen in the Gulf stream, that it grew on the Florida rocks, and by the influence and extension of the current, was detached and carried into this part of the Atlantic. However, this position is not tenable, as a single branch of fucus has never been found on the Florida reef. Humboldt, and other scientific men, are of opinion that this weed vegetates at the bottom of the ocean--that being detached from its root, it rises to the surface; and that such portion of it as is found in the stream, is drawn thither by the sweeping of the current along the edge of the weedy sea. Moreover, the fuci that are found in the northern extremity of the Florida stream are generally decayed, while those which are seen in the southern extremity appear quite fresh--this difference would not exist if they emanated from the Gulf.