HOW TO KNOW THE FRESH-WATER ALGAE 



48b Chloroplast covering almost the entire wall; cells variable in size 

 within the colonial mucilage. Fig. 42 CHLOROCOCCUM 



Fig. 42. Chlorococcum humicola (Naeg.) Rab. Cells 

 occasionally are seen to be inclosed in a mucila- 

 ginous sheath. 



Although this plant occurs on soil it reproduces 

 by swimming reproductive cells (zoospores). An- 

 other species, Chlorococcum infusionum (Schrank) 

 Menegh. is aquatic and is differentiated from C. 

 humicola by the fact that its cells are all uniform 

 Figure 42 in size and shape. Old, wet bones, and rocks un- 



der dripping water are favorable places for both 

 species. Unless it is Pieurococcus CProfococcusJ, Fig. 66, Chlorococcum 

 humicola is probably the most widely distributed algal species in the 

 world. 



49a (39) — Colony fusiform, definite in shape. See Fig. 38 



ELAKATOTHRIX 



49b Colony not fusiform, but cubical, globular quadrate, or irregular 

 in shape 50 



50a Colony regularly spherical, oval, or a rectangular plate 



61 



50b Colony irregular or some other shape (but young stages of Tetra- 

 spora. (Fig. 35), may be somewhat spherical) 51 



51a Colony of 4 cells in one plane interconnected by strands, the cells 



bearing a scale-like fragment of mother-cell wall. Fig. 43 



CORONASTRUM 



Fig. 43. Coronastrum aestivale Thompson. 

 (Redrawn from Thompson.) 



This is a very rare alga and the only one 

 of three species in the genus which has been 

 reported from America. The arrangement 

 of the cells and their distinctive wing-like 

 scale make it easy of identification. 



Figure 43 



42 



