THE PROBLEM OF SEX IN PLANTS 



345 



some of the lowest forms, cell-division always results in 

 reproduction, in the higher forms it only paves the way 



FIG. 251.- Spirogyra sp. A, terminal portion of vegetative filament; 

 B, stages of scalariform conjugation; C, preparation for lateral conjuga- 

 tion; D, zygospores formed by lateral conjugation. 



to increasing the size of the given individual, that is, to 

 growth. In other words, between cell-division and re- 



