268 



found. The tetrasporangia occur in the upper part of the fila- 

 ments and are rather scattered, being either solitary or a few 

 together, with sterile segments between. The tetrasporangia are 

 about 70 IJL broad. 



As I have previously pointed out 1 ), this species is found 

 upon the roots of the mangroves in the lagoons; but it occurs 

 also in the sea in deep water, about 8 fathoms or more. 



It has already been found at St. Croix by 0RSTED. It seems 

 to be not altogether common on the islands. 



St. Croix: Christiansted's Lagoon, Salt River. St. Thomas: Bovini 

 Lagoon. St. Jan: Off America Hill. 



Geogr. Distrib.: West Indies. Key West. 



2. Polysiphonia spec. 



Some small tufts of a quite sterile Polysiphonia were found 

 creeping upon old timber. It has four pericentral cells and its 

 branches are developed at the base of the trichoblasts. 



The basal part (Fig. 262) of the tufts is formed by decum- 

 bent, creeping filaments, composed of rather short cells, the seg- 

 ments being nearly as long as broad, about 50//. 



Often rhizoids are developed, from every segment, forming 

 in this way a long series (Fig. 262). The rhizoids have no cross 

 walls and end in a small disc fixed to the substratum. 



From these basal filaments the erect ones arise. At their base 

 these arc of nearly the same size as the basal ones, towards the 



upper part they taper 

 gradually to about one 

 half of their diameter. 

 The cells have nearly the 

 same length, being about 

 one to one and a half 

 times the breadth of the 

 filaments. In the upper 

 part of the filaments each 

 of the segments carries 

 a trichoblast placed in 

 a spiral line with a x / 

 divergency (Fig. 263). 



Fig. 262. Polysiphonia spec. 

 Base of a iilament. (About 80:1). 



*) B0RGESEN, F. The algal vegetation of the lagoons in the Danish West 

 Indies (Biologiske Arbejder tilegnede EUG. WARMING, K0benhavn 1911, 

 p. 48). 



