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



23 



Fronds tufted up to 20 cms high ; mostly nearly cylindrical, 

 sometimes somewhat compressed, the surface being more or less 

 uneven. It is irregularly ramified 

 (Fig. 14) ; the ramification is mono- 

 podia!, but the lateral branches are 

 often vigorously developed in this 

 way being more orlesspseudodicho- 

 tomious and the apices of the bran- 

 ches in the same time getting an 

 antler-like appearance (Fig. 15 a, b, c). 



The thallus is hollow (Fig. 16) 

 with the exception of the lower- 

 most part where the interior of the 

 tubular frond is filled with hyphal 

 filaments growing downwards from 

 the innermost cells (Fig. 15 d). These 

 filaments together with numerous 

 rhizoids growing out from the 

 peripheral cells in the basal part 

 of the frond form a small disc by 

 means of which the plant is fastened 

 to the substratum. 



The growth takes place by 

 intercalary division through the 

 whole thallus ; yet we may conclude 

 that a vigorous division of cells also 

 takes place in the ends of the 

 branches though any true apical 

 cell division is out of the question. 



The diameter of the thallus 

 reaches about 2 mm. The branches 

 taper somewhat towards their apices 

 and also sometimes towards their 

 bases. 



In a transverse section (Fig. 

 16) the thallus is seen to consist 

 of 3 — 4 layers of cells; these are 

 small, epidermal-like with rather 

 thick walls at the surface, large, 

 irregularly roundish-polygonal with 

 thin walls against the hollow interior. Seen from above the surface 

 cells are irregularly polygonal (Fig. 15 /) ; the cells in the interior, 



Fig. 14. Rosenvingea Sanctæ Crucis 



nov. spec. Habit of plant. 



(About natural size). 



