66 



Plant Life and Evolution 



curious free-swimming algae, the Volvocales, that 

 'hey might readily be mistaken for them. 



This frequent reversion to the free-swimming 

 condition, resembling in all respects the fully devel- 



Evolutlon of the sexual reproduction in the algae, showing 

 parallel development in the green and brown algae. Upper 

 figures, Chlorophyceae ; lower figures, Phaeophycese ; a, female 

 gamete; b, male gamete. 



i, Pandorina ; 2, Aphanochaete ; 3, CEdogonium ; 4, Ectocar- 

 pus; 5, Cutleria; 6, Fucus. 



Figs. I 5, after Oltmanns. 



oped cells of the lower organisms, is one of the 

 strongest reasons for assuming that the green algae, 

 at least, are derived from flagellate ancestors. 



Evolution of Sex in Algae. Among the algae 

 are found a number of groups in which are exhib- 



