Semi-Centennial Volume. 157 



CLASS IV. 



CHLOROPHYCEJE are algae characterized by true grass-green color; 

 single or united into threads, plates or masses; pyrenoids mostly present; 

 reproduction by zoospores, akinetes and aplanospores. 



Key to Orders of Chlorophyceas. 



Frond of one or moi'e cells. 



* Vegetative cells ciliate and motile, always or except during 

 resting periods, or easily passing into a motile condition, 



II. Volvocales. 



* * Vegetative cells motionless; reproductive cells motile or not. 



o. Reproduction by zygospores formed by the union of 2 



non-ciliated gametes I. Conjugales. 



b. Reproduction by zoospores, not by zygospores. 



1. Cells solitary or in a spherical or netlike combina- 

 tion III. Protococcales. 



2. Cells forming simple or branched filaments. 



* Cells uninucleate, chromatophore usually single, 



disk-, net-, or star-shaped IV. Ulotrichales. 



* * Cells multinucleate, chromatophore net-shaped, 

 as of numerous small disks in a cell. 



V. SiphonocUtdiales. 

 Order I. CONJUGALES. 



Key to Families of Conjugales. 



I. Cell wall mostly constricted into symmetrical halves with a differ- 

 entiated outer layer; solitary or in filaments; cell division follows 

 a fixed type, with interpolation of the younger halves between the 

 old ones 1. Desmidiacese, 



II. Cells cylindrical, without constrictions, always united in filaments; 

 the new filament always formed directly from the zygospore. 



■^ The entire protoplasmic contents of the conjugating cells 

 uniting to form the spore 2. Zygnemacese. 



* * Only a part of the contents of the conjugating cells used 



for the spore 3. Mesocarpaceae. 



Family I. Desmidiace.^:. 

 Key to Genera of Desmidiacese. 



I. Cells not united into filaments, more or less crescentic. 



1. Closterium. 

 II. Cells constricted in middle, dumb-bell shaped; end view not angular, 

 margins smooth, dentate or crenate but no spines. . . .2. Cosmarinm. 

 1. Closterium. 



Key to Species. 



I. Cells slightly curved; ends not contracted, but tapering, acute with 

 40-50 mic. length 5-12 times the width; chlorophyll bands, several 



granules in one row C. lanceolatum. 



II. Cells conspicuously curved, often subsemicircular; width 16-25 mic, 



cytioderm smooth C. Dianse. 



US. C. lanceolatum Kuetzing. 



Kansas: Burlingame, August, 1915; Horton, October, 



1916. 

 Colorado (15); Iowa (4); Nebraska (25). 

 U- C. Diana; Ehrbg. Plate III, fig. 14. 



Kansas: Neodesha, November, 1915; Horton, June, 



1916. 

 Iowa (4); Nebraska (25). 



