HOW TO KNOW THE FRESH-WATER ALGAE 



21b Cells of 2 sizes within the same colony, the smaller arranged at 

 one pole of the envelope. Fig. 18 PLEODORINA 



Fig. 18. Pleodorina illinoisensis Kofoid. 

 Another common species (P. califoi- 

 nica Shaw) has about one-half of the 

 cells larger and with reproductive 

 capacity, the smaller cells being 

 strictly vegetative. 



®k< 





Colonies are perfectly spherical like 

 most Volvox (Fig. 15) but have many 

 fewer cells (usually 128). Although PJeo- 

 dorina often occurs in the same habitat 



with Voivox it can be distinguished quickly by the two sizes of cells 



in the colony. 



Figure 18 



22a (12) — Protoplast at a considerable distance within the cell wall 

 and connected to it by fine, radiating processes; cells with a mass 

 of red pigment often present in the center of the protoplast (some- 

 times masking the green color); usually encysted, forming rust- 

 colored encrusting growths in bird baths and cemented pools. 

 Fig. 19 HAEMATOCOCCUS 



Fig. 19. Haematococcus lacustris (Girod.) 

 Rostaf. a, swimming cell showing pro- 

 toplast with radiating processes; b, 

 cysts (which usually are brick-red in 

 color). 



The wide gelatinous wall with fibrils 

 of protoplasm extending out from the 

 cell membrane identify this motile or- 

 ganism. It is widely distributed and a 

 common inhabitor of garden pools and 

 catch basins in rocks. 



Figure 19 



22b Cells not as above; free-swimming 23 



23a Cells with a definite (although sometimes thin) wall, often with a 

 gelatinous sheath 24 



23b Cells without a definite wall; chloroplasts lying against the cell 

 membrane; gelatinous sheath wanting 32 



30 



