F. Børgesen: Rhodophyceæ of the danish W. Indies. 



301 



The main filaments increase by means of a large apical cell 

 from which flat segments are cut off (Fig. 301), Alternately, from 

 «ach of these, branches issue forming two opposite rows. 





p. 



Fig.300. Bostnjchia tenella{W d\\\) J. Ag. 



Transverse section of the thallus. 



(About 150:1). 



Yig.oQl.Bostrychiatenella{Wdh\)i. Ag. 



Top of a filament. 



(About 200:1). 



My specimens belong to the typical form, having the side- 

 branches arranged distichously. 



Bostrychia tenella is fastened to the substratum by means of 

 vigorous rhizoids growing out anywhere from the fdaments (Fig. 

 299). As described by Falkenberg these haptera consist of con- 

 genital outgrowths from a group of surface cells, these at first 

 forming together a vigorous stem, later becoming more or less 

 separated or broadened out to a small disc (Fig. 302). 



Upon a transverse section of the main stem it 

 is seen that the central and pericentral cells have 

 very thick and stratified walls (Fig. 300). 



Plants with tetraspores and cystocarps are found. 



The stichidia are formed in the ends of the 

 ramuli and have mostly four, sometimes fewer, verti- 

 cillated sporangia in each segment. 1 have not ob- 

 served any tendency to uniseriated stichidia. The 

 sporangia are tetrahedrically divided. 



The cystocarps (Fig. 303) are placed in the sum- 

 mits of the side-branches. Their shape is spherical- 

 urceolate. 



Bostrychia tenella was originally described by Vahl 

 from specimens from St. Croix. 



It occurs both in sheltered and in more exposed places, and 

 where it is constantly moistened by the spray it is able to grow 

 somewhat above the surface of the sea, especially when found 



Fig. 302. 

 Bostrychia 

 «eneZZa (Vahl) 

 J. Ag. End of 

 ayounghap- 

 ter. (About 

 125:1). 



