Sentence:  It is well known to seamen, and others who have crossed the Atlantic ocean, that a certain part of that sea is generally covered more or less with a particular species of weed, called gulf-weed, but the reason of its accumulating there, and its origin, have given rise to much difference of opinion. [...] [T]he part of the ocean in which it is found is usually called the <WSD>Sargasso</WSD> sea. The <WSD>Sargasso</WSD> weed is also familiarly called tropical grapes, from being found in the vicinity of the northern tropic, but it is most generally known by the name of <WSD>Sargasso</WSD> or gulf-weed. 
Meaning of the word marked with <WSD> tags:  A brown alga, of the genus "Sargassum", that forms large, floating masses.