228 ESSENTIALS OF BOTANY 



(h) The shape and size of the larger organ. It is an oogonium, 

 containing many nuclei. Within the oogonium is developed an egg, 

 which after fertilization becomes an oospore. 



(c) The shape, size, and thick cell-walls of the mature oospores. 



293. Discussion. — Vaucheria differs greatly from Spiro- 

 gyra and from most of the green algse. The filaments are 

 not composed of separate cells, but the long branching tube 

 is a complex cell with many nuclei. The spore-cases of 

 the zoospores, the antheridia, and the archegonia are of 

 course additional cells or cell groups growing from the 

 filament. 



The process of sexual reproduction in Vaucheria consists 

 of the union of the protoplasm of a sperm with that of an 

 egg. This union is quickly followed by the development 

 of a heavy cell-wall about the fertilized egg. The oospore 

 thus formed can resist unfavorable conditions much longer 

 than the mature plants could do so. After a resting period 

 the spore germinates and produces a new individual. 



Vaucheria belongs to a considerably higher stage of de- 

 velopment in the plant world than Spirogyra does. This 

 is shown especially by two important points of difference.^ 



1. Vaucheria has one kind of cell for doing the vegeta- 

 tive work of the plant (photosynthesis, etc.) and other kinds 

 for reproduction. In Spirogyra all the cells appear alike. 



2. In Vaucheria the gametes are unlike. The sperms 

 and the eggs are not only very unequal in size, but they 

 differ much in structure and in power of movement, the 

 sperms being freely motile while the eggs are stationary. 

 In Spirogyra any gamete appears to be like all the others. 



1 These have already been stated in Sect. 28S, but as (Edoffonium is more- 

 likely to he omitted Irom a brief course than Vaucheria it seems best to repeat 

 the statement. 



