THE GKEEK ALGLE (CHLOROPHYCE^) 203 



to form zygospores, which constitutes the simplest kind of 

 sexual reproduction. In Spirogyra, zygospores are formed by 

 the union of similar gametes, the conjugation being brought 

 about by siphon-like tubes which unite the cells from which 

 the gametes come. In VaucJieria the gametes are differentiated 

 into an egg and a sperm, which, by fertilization, produce an 



FIG. 166. Zygnema 



A, two vegetative cells showing the central nucleus which lies between the parts of 

 the dumb-bell-like chloroplast. B, conjugation to form zygospores; a, b, c, conju- 

 gating tubes ; z, zygospore fully formed. Both greatly enlarged, but A more than B 



oospore. These differentiated gametes are found in specialized 

 sex organs made primarily for reproductive work. 



187. Other green algae. 1 The green algse are more abundant 

 than all others in inland waters, and it is not possible or de- 

 sirable to mention many of them in this connection. Some of 

 the following may be collected, however, in regions in which 

 those already discussed are found. Sphcerella, a unicellular 



1 It is more important that the student should have an impression of the 

 kinds of plants found among the algae than that he should remember names 

 of different genera. 



