ULOTHRIX. 33 



gives the plant advantage over the plants heretofore con- 

 sidered, because it provides for more certain and rapid 

 multiplication and wider distribution. 



Sometimes bodies like zoospores, but not true spores 

 at all, since they do not reproduce the kind of plant that 

 formed them, unite, thus forming a spore. When two of 

 these bodies unite (whence called gametes) they form a spore 

 which can reproduce the kind of plant that formed them. 

 Such a spore is sexual since it is formed by the union 

 of cells, and this one being formed by the conjugation 

 (yoking together) of similar gametes is called a zygospore 

 (to yoke; spore). Observe that gametes from widely 

 separate individuals may unite, thus bringing into the 

 sexual spore protoplasm widely separated in origin. 

 It is evident that reproduction by zoospores involves no 

 opportunity of introducing new vigor from a second plant 

 as does reproduction by sexual spores- But it must be 

 kept in mind that sexuality in plants originated from 

 the non-sexual processes of zoospore formation, and that 

 zoospores are the cells that begin to function as gametes. 

 From the condition illustrated by Ulothrix there begins a 

 highly important series of differentiations of gametes 

 looking toward the formation of the sexual spore. 



