HOW TO KNOW THE FRESH-WATER ALGAE 



13a Cells arranged in a plane, forming a plate (flat or twisted) 14 



13b Cells arranged to form a spherical, ovoid or spheroidal colony. .15 



14a Colony horseshoe-shaped, flat or twisted. Fig. 9. . .PLATYDOR1NA 



Fig. 9. Platydorina caudatum Kofoid. The fla- 

 gella of the organism in the center of the 

 colony are directed vertically to the surface. 



Although rare this plant can be easily 

 identified by the flattened, slightly twisted, 

 horseshoe-shaped colony. It is to be found 

 in the same habitats with other members of 

 the Volvocaceae, Eudorina (Fig. 17), and Pan- 

 dorina (Fig. 14). 



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u 



\ 



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Figure 9 



14b Colony a circular or subquadrangular plate. Fig. 10. . . .GONIUM 



A 





' ,A £31 U;, 



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Fig. 10. Gonium pecforaie Muell. An 18- 

 celled colony. 



The number of cells in a colony may vary. 

 Other species (with cells shaped differently) 

 may have as few as 4 or as many as 32-64 

 individuals. The rectangular plates tumble 

 over and over as the colony swims through 

 the water. 



Figure 10 



15a Colony oblong or pear-shaped, with cells densely clustered and 

 all directed anteriorly, without an enveloping colonial mucilage. . 16 



15b Colony globular or ovoid; cells inclosed in a mucilaginous sheath, 

 but not all directed one way 18 



26 



