108 WISCONSIN PETTOPLANETON 



Family PROTOCOCCACEAE. 



Cells solitary and spherical; or in colonies containing an indefinite 

 number of cells that are spherical and mutually compressed or in very 

 short irregular filaments. Cell wall delicate to heavy, smooth or vari- 

 ously sculptured. Chloroplast single, parietal and disciform, with or 

 without pyrenoids. Cells capable of vegetative division. 



Reproduction, aside from vegetative division of cells, by zoospores or 

 aplanospores. 



KEY JO THE GENERA. 



Cell wall thin, smooth CHLOBELLA 



Cell wall thick, sculptured TBOCHISCIA 



CHLORELLA Beyerinck 1890. 



Cells small, spherical ; solitary or in small colonies of indefinite shape. 

 Chloroplast disciform to cup-shaped, with or without a pyrenoid. 



Reproduction by the division of cell contents into 2-4-8 daughter 

 cells. Resting akinetes known. 



CHLORELLA VULGARIS Beyerinck. PI. 22, Fig. 1. 



Bot Ztg. 48: 758, pi. 7, figs. 2^-2\ 18&0. 



Cells spherical, generally solitary. Chloroplast parietal, cup-shaped, 

 with or without a pyrenoid. Cell wall smooth and delicate. (Faculta- 

 tive Planktont). 



Diam. cells 5-10 /u, 



Mendota (rr). 



C. vulgaris is a minute alga and one that is easily overlooked. The 

 record of its occurrence in Lake Mendota is based upon its isolation by 

 pure culture methods from a plankton catch. It is very probable that 

 it is present in other lakes but has been overlooked. 



i 



TROCHISCIA. Kiitznig 1845. 



Cells spherical to sub-spherical, solitary or in small clumps. Cell 

 wall fairly heavy, areolate or ornamented with spines, denticulations, 

 ridges, or other projections. Cells generally containing several parietal 

 disciform chloroplasts each with a pyrenoid. 



Reproduction by vegetative cell division or the formation of 4-16 

 aplanospores that are liberated by the dissolution of the old mother 

 cell wall. 



