DEVELOPMENT OF PLANTS 



187 



sionally be noted, such as the development of gametospores in 

 either filament or the fusion of the adjacent cells of a filament by 

 means of lateral tubular outgrowth. In other genera, there is a 

 considerable modification in the process, as in some species of 

 Zygnema, where the fusion is effected in the middle of the tube. 



FIG. 107. Sexual reproduction of Spirogyra: A, in lower portion of figure 

 the formation of the tubes between the opposite cells of the filaments is shown. 

 Above the contents of two cells have united with two cells of another filament, 

 forming two gametospores. B, germination of a gametospore. 



This is only a different form of the sexual process with which 

 you are familiar, the difference being, that but one gamete is 

 formed in each cell and these bodies are motionless or at least 

 not provided with cilia and do not escape from the mother plant. 

 When the fusion of the gametes has been effected the resulting 



