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TEXTBOOK OF BOTANY 



reduction division occurs; and, except for mutations, all the cells of 

 Pleurococctis have the same chromosome complement. It is a non- 

 motile one-celled plant, though several plants may remain attached 

 temporarily as an unorganized colony. 



Fig. 278. Forms of cells of a Pleurococcus. Species of this genus of green algae 

 are non-motile and mostly aerial. The individuals are usually one-celled, though 

 they may remain united in colonies temporarily as indicated in the drawing. 

 Species of this group are the algae most frequently found in lichens. 



Chlamydomonas. In contrast to the one-celled non-motile Pleuro- 

 coccus is the one-celled motile Chla7mjdomonas (Fig. 279). It is often 

 found as a part of the plankton, sometimes occurring in large numbers in 

 small pools or even in indoor aquaria. The cell is spherical, ovoid, or 

 elongate, and often flattened. Two flagella project from the anterior end. 

 Both spore formation and sexual reproduction occur. 



Fig. 279. Forms of vegetative and reproductive cells of a Chlamydomonas. 

 Species of this genus of green algae are one-celled and motile. They reproduce 

 vegetatively by motile spores and sexually by the union of gametes as indicated 

 in the drawing. 



Cells with flagella similar to Chlamijdomonas may remain attached 

 and thus form definite colonies of several to many cells. Examples of such 

 colonial algae are Pandorina, Eudorina, and Volvox (Fig. 280). All of 

 these algae are termed flagellate organisms. 



Ulothrix. In the spring one may see bright green slimy filamentous 

 growths of Ulothrix on the stones and rocks of the shores of streams, 

 lakes, and ponds. Since the cylindrical cells of this alga are joined end 



