20 Mindeskrift for J. Steenstrup. XXXII. 



In respect to the second, coarser form which I have found in the Sargasso Sea 

 this reminds very much of Sargassum Hystrix which is said to be widely dispersed 

 along the shores of the West Indies and America. As I have pointed out above, 

 the figure of the sterile plant in J. Agardh's "Species Sargassorum Austr.", pi. 1, 

 fig. 1 agrees very well with the floating form; only the leaves in the floating form 

 are commonly somewhat smaller, and proportionally more serrate, and so along their 

 whole length, moreover the vesicles are very numerous. In the collections of the 

 Botanical Museum, Copenhagen, some specimens were found, collected floating by 

 Capt. Andrea in the Old Bahama Channel, '/Vm 1870 and by J. Agardh referred to 

 this species. These specimens agree also very much with my specimens from the 

 Sargasso Sea. Therefore I feel quite convinced that this form has its origin from 

 Sargassum Hystrix being a floating form to which I have proposed the name 

 var. fluitans. 



The results of the present investigation are in brief: 



1) The floating Sargassum in the Sargasso Sea consists of two species: Sargassum 

 natans (L.) (the most common) and S. Hystrix J. Ag. var. fluitans. 



2) The Gulfweed is a true pelagic alga; it is a perennial, lives and dies out at 

 the sea. 



3) As to the origin of the Gulfweed, I presume, it most probably has descended 

 from forms living at the shores of the West Indies and surrounding coast of America. 



It is, thus, of great interest that we have before us an instance of floating, 

 pelagic species of such a high alga-type as Sargassum. Because, as is well-known, 

 the higher types of algæ are as a rule attached, at least normally, and if detached 

 they perish sooner or later. 



Finally I wish to point out that the amount of organic detritus which the 

 floating pelagic Sargassum produces surely may be of high importance to the 

 economy of the sea, and so much the more to the tropical sea, where the Plankton 

 is more scant ^). 



Since the printing of this paper was nearly ended Mr. Winge has published a small note 

 on the Gulfweed in the last number of the "Botanisk Tidsskrift", vol. 33, Heft. 4, p. 269. 

 Having not seen the Sargasso Sea himself, Mr. Winge's observation is not based upon material 

 collected by himself. His results are: 1) The Gulfweed essentially consists of two species: 

 Sargassum bacciferum and S. vulgare, 2) The Sargassum can surely float for some time and 

 reproduce vegetatively. Finally some information is given about the location of the Sangasso Sea. 



') Compare H. H. Gran, 1. c. p. 366. 



