F. Borgesen: Phæophyceæ of the Danish W. Indies. 



35 



nearly always stalked, having a single basal cell, very seldom I 

 have found sporangia without this cell. They are oblong-pyri- 

 form; but as to the form and size some differences occur. In 

 one specimen from the reef between the Hurricane Island and 

 St. Thomas they were nearly oval-pyriform, 75 p long and 30 p. 

 broad and the assimilating filaments about 100 p long (Fig. 22 a); 

 in another specimen collected at the French wharf in the harbour 

 of St. Thomas they were much longer, oval-pyriform to clavate 



Fig. 22. Ralfsia expansa J. Ag. 

 a and b, unilocular sporangia ; c, plurilocular sporangia. 



(About 300 : 1) 



until 120 p long without the basal cell and 30 p broad and the 

 assimilating fdaments up to 170 p long (Fig. 22 b). 



The assimilating filaments consisting of from 8 to 14 cells are 

 thinnest (about 3 p.) and the cells of which they are composed 

 longest somewhat below their middle, the cells growing thicker 

 and shorter towards their base and especially towards their top, 

 the filaments assuming herewith a clavate appearance. 



The plurilocular sporangia (Fig. 22 c) are formed by the 

 assimilating filaments, the cells in their uppermost part being 



