HOW TO KNOW THE FRESH-WATER ALGAE 



268a (266) Growing on submerged wood and stones with a prostrate 

 cushion-like mass of branches from which vertical branches arise. 

 See Fig. 185 GONGROSIRA 



268b Thallus formed differently 269 



269a Plants growing on shells of turtles; branching arising only from 

 the base of the main lilament. Fig. 190 BASICLADIA 



Fig. 190. Basicladia Chelonum (Collins) Hoffman & 

 Tilden. a, cells at base of filament; b, branch- 

 ing habit; c, series of sporangia formed in upper 

 portion of filament. 



This and 1 other species (differentiated mostly 

 by size) comprise the genus which is distinctive in 

 that the plants occur only on the shells of turtles, 

 especially the snapper. Old turtles are usually 

 "mossy" with the tufted growths of filaments which 

 characteristically branch so close to the base that 

 the branching habit is easily overlooked. Cells 

 may be as much as 120 fx in diameter but a milli- 

 meter or two in length. 



269b Plant not growing on turtles, or with other types of branching. .270 



270a Plants showing basal-distal differentiation, usually attached (float- 

 ing in age); branching arbuscular (tree-like or bush-like) 271 



270b Plants not forming bushy growths 274 



271a Cells with haematochrome (reddish color in the chloroplasts). 

 See Fig. 171 TRENTEPOHLIA 



271b Cells without haematochrome 272 



119 



