HOW TO KNOW THE FRESH-WATER ALGAE 

 265b Thallus not a dense tuit of yellow-green filaments 266 



266a Bearing enlarged, thick-walled akinetes (vegetative spores) among 

 the cylindrical cells of the filament, or with spores at the ends 

 of branches 267 



266b Without akinetes 268 



267a Akinetes globular. Fig. 188 CTENOCLADUS 



Figure 188 



Fig. 188. Ctenocladus circinnatus Borzi., showing a terminal series of 

 akinetes. 



This is a branched filamentous species, growing epiphytically on 

 angiospermous plants in brackish water. The chains of globular 

 akinetes at the ends of branches make it distinctive, although the 

 habit of growth is somewhat like Gongrosira (Fig. 185). 



267b Akinetes barrel-shaped or oval. Fig. 189 PITHOPHORA 



Fig. 189. a, Pithophora Mooreana Collins; b, P. Oedogonia (Mont.) 

 Wittr., showing a sample of the chloroplast. 



ek ^> 







Figure 189 



There are 3 or 4 species of this irregularly 

 branched, filamentous genus in this country, dif- 

 ferentiated by dimensions of the filament and by 

 size and shape of the much-swollen akinetes that 

 are formed intermittently throughout the plant. 

 When occurring in laboratory aquaria, having 

 been brought in on material obtained from bio- 

 logical supply houses, the filaments often fail 

 to develop akinetes, the cells becoming exceed- 

 ingly long and lose some of the appearance by 

 which they are usually identified. 



118 



