102 



MORPHOLOG Y. 



forms two spermatozoids (sometimes only one) which are of the same form as 

 the zoogonidia but smaller, and yellowish instead of green. In some species 



a motile body intermedi- 

 ate in size and color be- 

 tween the spermatozoids 

 and zoogonidia is first 

 formed, which after 

 swimming around comes 

 to rest on the oogonium, 

 or near it, and develops 

 what is called a "dwarf 

 male plant " from which 

 the real spermatozoid is 

 produced. 



243. Oogonia. — The 



Fig. 98. 

 Portion of thread 

 o f cedogonium 

 showing antheridia 



Fig. 99. 

 Portion of thread of cedo- 



gonium showing upper half oogonia are formed di- 



to Z mdre?d?'toenter SP (ATter rectl y from one ° f *e 

 Oltmans). vegetative cells. In most 



species this cell first enlarges in diameter, so that it is easily detected. The 



protoplasm inside is the egg cell. The oogonium wall opens, a bit of the 



protoplasm is emitted, and the spermatozoid then enters and fertilizes it 



(fig. 99). Now a hard brown wall is formed around it, and, just as in spirogyra 



Fig. 100. Fig. 101. Fig. 102. 



Male nucleus just entering Male nucleus fusing with The two nuclei fused, and 

 egg at left side. femaie nucleus. fertilization complete. 



Figs. 100-102. — Fertilization in cedogonium. (After Oltmans). 



a.nd vaucheria, it passes through a resting period. At the time of germination 

 it does not produce the thread-like plant again directly, but first forms four 

 zoospores exactly like the zoogonidia (fig. 103). These zoospores then 

 germinate and form the plant. 



244. CEdogonium compared with spirogyra. — Now if we compare cedo- 

 gonium with spirogyra, as we did in the case of vaucheria, we will find here 

 also that there is an advance upon the simple condition which exists in spiro- 

 gyra. Growth and division of the thread is limited to certain portions. The 

 sexual organs are differentiated. They usually differ in form and size from 

 the vegetative cells, though the oogonium is simply a changed vegetative 



