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



281 



part of their thallus, 

 this also being the case 

 with P. ferulacea as 

 mentioned above. 



St. Thomas: The 

 reef between the Hiirri- 

 cane Island and St. Tho- 

 mas. Store Nordsidebugt. 

 St. Croix: Northside. 



Geogr. Distrib.: 

 Mexico, West Indies, Au- 

 stralia. Sandwich Islands. 



Digenia Ag. 



1. Digenia simplex 



(Wulf.) Ag. 



Agardh, C, Spec. Alg., 

 Syst. p 



p. 389 

 Agardh, Alg. 



Fig. 280. Polysiphonia ferulacea Suhr, J. Ag. 



Part of a filament with a nearly ripe cystocarp. 



(About 125:1). 



Fig. 281. Digenia 

 simplex (Wulf.) Up- 

 per end of branch 

 with tetrasporan- 

 gia. (About 125:1). 



194. J. 

 Medit., p. 



147; Spec. Alg., vol. II, pars 3, p. 845. Harvey, W. H., 

 Nereis Bor.-Am., part II. p. 30. Falkenberg, P., 

 Rhodomelaceen, p. 159, pi. 9, figs. 25- 29. 



Conferva simplex Wulf., Cryptogama Aquatica, 

 p. 17. 



Cfr. De-Toni, Sylloge Alg., vohlV, p. Ill, p. 963, 

 where more synonyms are named. 



Regarding its anatomy and morphological 

 building upon the whole I refer to Falkenberg's 

 exhaustive description 1. c. 



Digenia simplex occurs both in shallow 

 water and rather exposed places and in deep 

 water. The different localities determine to a 

 large extent the development of the plant; in 

 the first mentioned places the plant is robust, 

 of low growth, about 5 — '6 cm high and much 

 ramified, in deep water on the other hand I 

 have gathered specimens about 20 cm high and 

 nearly unbranched. 



Its stiff, tough stem is a very attractive 

 growing place for numerous small algæ which 

 commonly cover its thallus to such an extent 

 that only the quite young tips are free. 



