F. Børgesen: The Species of Sargassum. 19 



Naturally this circumstance is a serious obstacle in respect to settling the que- 

 stion of origin, or better the original home of the floating Sargassum, inasmuch 

 as there is some possibility of the Sargassum descending from forms that are in- 

 habitants of other coasts of the Atlantic ocean than just the West Indian. However, 

 in favour of the West Indies with adjoining shores being the original home of the 

 floating Sargassum, is the faet, that the importation seems more possible from there, 

 besides that certain species of Sargassum occur there, which do resemble the floating forms. 



The species which, according to my opinion, are the most obvious as to the 

 origin of S. natans are: Sargassum i^ulgare and Sargassum Filipendula; both show 

 much likeness with Sargassum natans and both are common along the shores of the 

 West Indies, and warmer parts of the American coast. 



In the following I shall try to explain my reasons for entertaining this view. 



In the collection of the Botanical Museum at Copenhagen a large specimen of a 

 Sargassum is found taken by Capt. A. Andrea in the Atlantic upon 28'' lat. N. and 

 81° lat. W., consequently quite near the shore of Florida. J. Agardh has deter- 

 mined this specimen as S. a§ine, a form belonging to S. Filipendula. This specimen 

 was interesting in several respects. Judging from its appearance it has evidently 

 been floating already for some length of time, but nevertheless it is fertile. The 

 respectacles are very thin, cylindric and much ramified ; the leaves are narrow, nearly 

 linear, with serrate margin, and have a distinct midrib, but no cryptostomata; the 

 vesicles are large, spherical. It can not be denied that this specimen resembles 

 much Sargassum natans; the shape of the leaves is proportionally a little broader 

 than in Sargassum natans, but the cryptostomata are wanting as is the case with 

 S. natans. Furthermore the vesicles are perhaps a little larger in this specimen than 

 in S. natans, but taken altogether, the differences are not great. As mentioned 

 above (p. 12) some few specimens of f ruiting floating Sargassum have been recorded; 

 upon such specimens recently detached, and yet fertile are based, I presume, these 

 statements. 



But even if this form of Capt. Andrea approaches S. natans it appears to me 

 that S. natans may also have descended from S. vulgare. Narrow leaved forms of 

 this species occur (comp. f, i. Kutzing's figure in "Tab. Phycol.", vol. XL, pi. 23, 

 fig. II) and these forms agree very much with S. natans. In some of my attached 

 specimens from the Danish West Indies, I have, now and then, found leaves without 

 cryptostomata. And in regard to the flagellate prolongation known from var. ciliata 

 of S. natans I may point out that I have often found a shorter or longer, frequently 

 leaflike prolongation upon the top of the vesicles. And taking into consideration 

 the above mentioned tendency to proliferations in loose-lying algæ the frequency of 

 these ciliate prolongations in the floating seems very natural. 



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