THE FRESH-WATER ALGAE 151 



121 (124) Cells spherical I2 2 



122 (123) Chromatophore single Sphaerocystis Chodat. 



Colonies large; clusters widely separated from 

 each other. Gelatinous envelop invisible without 

 reagents. Chromatophore thin, parietal, with a 

 pyrenoid on one side and an opening on the other. 

 Reproduction by internal division. 



Sphaerocystis^ is almost universally found in the 

 plankton and is one of the most conspicuous and 

 beautiful of all the plankton forms. Sometimes the 

 colonies are very large, consisting of many clusters. 



FIG. 167. Sphaerocystis schraeteri Chodat. 

 (Original.) 



X 520. 



123(122) Chromatophores many, parietal Chlorobotrys Bohlin. 



Cells spherical, in a gelatinous matrix, as in Sphaerocystis, but the 

 chlorophyll in many parietal discs. 



FIG. 168. Chlorobotrys regularis Bohlin. X 300. (After West.) 



124(121) Cells not spherical 125 



125 (126) Cells crescent-shaped Kirchneriella Schmidle. 



Cells in clusters, as in Sphaerocystis, but strongly 

 crescent-shaped. 



In reproduction internal division takes place trans- 

 versely and the four or eight daughter cells are set 

 free by the breaking of the cell wall. 



Several species occur in the plankton. They also 

 occur in ponds among water plants. 



FIG. 169. 



KirchnerMla obesa Schmidle. 

 (Original.) 



X 600. 



126 (125) Cells oval or bluntly pointed Oocystis Nageli. 



Cells oblong, single, or two, four, or eight in a gelatinous 

 envelop; in some cases many clusters in a colorless gelatinous 

 matrix. Chromatophore single, parietal, with an opening on 

 one side, or of many small discs. Pyrenoids present in some 

 species. Cells' single or in clusters, as in Sphaerocystis, but 

 ellipsoidal in shape. 



Oocystis is frequently found in the plankton where it is 

 usually in large gelatinous colonies similar to Sphaerocystis 

 and Kirchneriella. In other localities the cells are generally 

 solitary. 



FIG. 170. Oocystis solitaria Wittrock. X 600. (Original.) 



