94 



ELEMENTARY BOTANY. 



central protoplasmic mass, and suspended by extensions to 

 the parietal layer (Fig. 119). The filaments elongate by the 

 growth and transverse division of the cells ; the protoplasm 

 divides, a cellulose wall is at the same time secreted, and the 



^Z 



Fig. 119. 



Fig. 120. 



two resultant cells then elongate to the normal length. Some- 

 times the filaments break up spontaneously, and each part 

 gives rise to a new filament. A form of reproduction (which 

 may be denominated sexual, the methods mentioned pre- 

 viously being called vegetative), takes place by the process 

 called conjugation (Fig. 120). From each of the cells of two 

 filaments lying parallel to each other, slight protrusions arise 

 and these grow toward each other until they come in contact 

 and unite. The partition between them becomes absorbed ; in 

 the meantime the protoplasm in each of the two cells con- 

 tracts, rounds itself, and one mass passes gradually through 

 the channel over into the other cell, where the two unite and 

 form the spore. Tlie old cell-walls decay and the spore fells 

 to the bottom of the water, there remaining till the process of 

 germination commences. 



