colonials are attached to submerged vegetation. The algal cells vary 

 in abundance so that the colony may be Hght or very dark accord- 

 ingly. The protozoan inhabits mostly hard water lakes where it is 

 frequently mistaken for Nostoc, Tetraspora, or some other gelatinous 

 alga. Mich., Wis. 



CHLORELLA Beyerinck 1890, p. 758 



Unicellular, solitary or aggregated in irregular clumps; round or 

 ellipsoid; variable in size in the same habitat. Chloroplast a parietal 

 cup or merely a plate, with or without a pyrenoid. Reproduction by 

 4 or 8 daughter cells (non-motile) produced from the protoplast 

 of the mother cell. 



This small plant may be confused with species of Chlorococcum, 

 a soil or subaerial genus, from which it can be differentiated with 

 surety by a study of reproductive habits. It is very similar also to 

 many other unicellular green algae and may be confused with 

 motionless zoospores of some genera. It is necessary, therefore, to 

 study a large number of individuals, or better still to culture the 

 plants in making identification. 



Chlorella forms 4 or 8 daughter cells within the mother cell wall 

 whereas Chlorococcum produces biflagellate zoospores which escape- 

 and immediately separate from one another. In Chlorococcum the 

 chloroplast more nearly covers the cell wall than in Chlorella. 

 Chlorococcum lives almost entirely on or in soil, sometimes at con- 

 siderable depth, or on old wood and rocks. Chlorella is aquatic but 

 may share the same habitat with Chlorococcum. 



Beyerinck (1890) recommends combining Chlorella and Zoo- 

 chlorella, but for the reason mentioned above (under Zoochlorella) , 

 they are separated here. 



Key to the Species 



Cells ellipsoidal, 7-8/. in diameter, 9.5fi long C. ellipsoidea 



Cells spherical, usually 5-10/. in diameter C. vulgaris 



Chlorella ellipsoidea Gerneck 1907, p. 250 



PI. 53, Figs. 11, 12 



Cells ellipsoidal, sometimes unsymmetrical; chloroplast a folded 



plate over part of the cell wall; described as producing as many as 



32 autospores during reproduction; vegetative cells 7-8/x in diameter, 



9-9.5/A long. 



Generally distributed in many lakes and ponds. Mich., Wis. 



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