HOW TO KNOW THE FRESH-WATER ALGAE 



438b Cells not densely crowded but evenly spaced or regularly ar- 

 ranged 439 



°&® o ( 



439a Cells in one layer at the periphery of the mucilage. Fig. 319. 

 COELOSPHAERIUM 



Fig. 319. a, Coelosphaerium Naegeli- 

 anum Unger; b, C. Kuetzingianum 

 Naeg. 



There are 2 common species of this 

 genus which are members of the 

 open water plankton. As the name 

 suggests, the cells are arranged so 

 as to form a hollow colony. C. Nae- 

 gelianum has cells which contain 

 pseudovacuoles which are light re- 

 fractive and the colony appears 

 brownish-purple or even black rather 

 than blue-green when seen micro- 

 scopically. 



Figure 319 



439b Cells distributed throughout the colonial mucilage. Fig. 320 .... 



APHANOCAPSA 





Q 



03 





-•'• o o 

 n ° P) o '• 



% ° ft o° 



8o\° oo 



n O ^ OO- 



Oq O C9 

 . o<b o 



Fig. 320. a, Aphanocapsa Gie- 

 villei (Hass.) Rab.; b, A. elach- 

 ista West & West. 



Whereas Microsystis has 

 cells compactly arranged, in 

 this genus they are rather even- 

 ly spaced throughout the colo- 

 nial mucilage. The cells are 

 spherical and vary in size in 

 different species, some being 

 not much larger than bacteria 



and can be mistaken for them. Cells often appear in pairs. There are 



several species reported from the United States. 



Figure 320 



440a (437) Cells crowded, usually with refractive false vacuoles. See 

 Fig. 318 MICROCYSTIS 



440b Cells evenly spaced within the mucilage; false vacuoles lacking. 

 See Fig. 320 APHANOCAPSA 



182 



