HOW TO KNOW THE FRESH- WATER ALGAE 



60b Cells round or oval, not arranged in semi-opaque mucilage. See 

 Fig. 41b GLOEOCYST1S 



61a (50) Cells incised or constricted in the mid-region to form 'semi- 

 cells', the cells often interconnected by fine gelatinous strands. Fig. 

 50 COSMOCLADJUM 



GO © , 



Fig. 50. Cosmocladium tuberculatum Presc. 



This species has every appearance of a tiny 

 Cosmarium-like desmid (Fig. 113) in which the 

 cells are enveloped in a colorless, gelatinous 

 sheath. There are but few species in the genus, 

 occurring with other desmids in soft water or 

 acid bogs. Under favorable optical conditions 

 the fine intercellular connecting strands of mu- 

 cilage can be determined. 



Figure 50 



61b Cells not constricted to form 'semi-cells' 



62 



62a Chloroplast star-shaped, the radiating processes with their outer 

 ends flattened against the wall. Fig. 51 ASTEROCOCCUS 



Fig. 51. Asterococcus superbus 

 (Cienk.) Scherf. 



This species and A. limneticus 

 G. M. Smith are the only ones 

 known to occur in North America. 

 A. superbus may occur singly or 

 in colonies of 2 or 4 cells and 

 Figure 51 shows the star-shaped chloroplast 



more clearly than does the former 

 which has smaller cells, 8 to 12, rarely 16 in number within a common 

 envelope. A. limneticus, as the name suggests, is found in open water 

 plankton. 



62b Chloroplast not star-shaped 



63 



46 



