Horsburgh, in his Directory, mentions the range of the weed, as being first seen in latitude 24° or 25° north, and extending as far as latitude 40° or 42° north, but I regard the limits of its range as depending much on the prevailing winds blowing strong for some time in a particular direction. On the 3rd of March, 1831, I first saw the weed in latitude 20° 12′ north, longitude 35° 39′ west. In latitude 24° 16′ north, and longitude 36° 55′ west, large quantities of it were passed, and in latitude 37° 53′ north, and longitude 35° 32′ west, we left it. During this voyage it was first observed, as I have previously mentioned, on the 31st of March, in latitude 22° north, and 41° west longitude; and was seen in large quantities nearly the whole distance. From the trade wind being much to the northward, we were driven as far to the westward as 44° 7′, still continuing to have a quantity of weed about the ship; indeed it rather increased than diminished, for large masses were seen even thus far beyond the usual limit assigned to it; on the 12th of April extending to 38° 32′ north latitude, and 34° 30′ west longitude. The utmost western limit I had an opportunity of observing it in being 44° 7′, and the range of the temperature of the atmosphere in its limits being maximum 76°, medium 70°, minimum 59°. Of the genus _Sargassum_[95] there are numerous species distributed over the globe; but the _S. vulgare_, or _Fucus natans_, and other species, are also described as having their _habitat_ in the particular range I have before mentioned; but I have not been able to find more than one species, some sprigs of which exhibit anomalies, but not specific differences; for although apparently differing in having the leaves broader, and not so serrated at the edges, yet many of these were growing from plants which had not such distinctions. According to Greville, this genus, the most extensive of the FUCOIDEÆ, comprising above seventy species, is nearly confined to the two tropics, and examples rarely occur beyond the forty-second degree in either hemisphere:— “Flung from the rock on ocean’s foam to sail, Where’er the surge may sweep, the tempests breath prevail;” will only now be partly applicable to this weed, as it is tolerably well ascertained to vegetate floating on the water, each sprig becoming, as detached by the violence of the waves, the contact of ships, or other causes, a perfect and large plant.[96]