198 



HIGHER TYPES OF REPRODUCTION 



orders of the Chlorophyceae, some of which are marine, that 

 cannot be considered at this time. Two genera, however, de- 

 serve attention because they show significant advances in the 

 evolution of plant life. In Oedogonium, a member of a small 

 order, the Oedogoniales, we find a still higher form of the sexual 

 reproductive process. These plants are of very common occur- 

 rence in ditches, streams and springs where their filaments form 

 for a time greenish masses and coatings upon various objects, 

 but finally become detached and free-floating (Fig. 115, A). 

 Any of the cells of a filament, save the basal one, may form a 

 single zoospore, which are large pear-shaped bodies with a narrow 



Fig. 116. Sexual reproduction of Oedogonium: A, portion of a filament 

 in which a female gamete has been formed — 0, opening in cell wall for en- 

 trance of male gamete. B, portion of filament showing formation and es- 

 cape of male gametes. C, gametospore free from mother cell. The germi- 

 nation of this spore results in the rupture of its outer wall and the protrusion 

 of the contents of the spore as four cells which are for a time retained by the 

 delicate inner wall of the spore, as shown in D. E, the four cells have become 

 mobile zoospores and the delicate inner wall of the gametospore is greatly dis- 

 tended and about to rupture. F, G, stages in the germination of the zoospore. 

 — ^After Hirn. 



colorless end around the base of which arise a circle of numerous 

 cilia (Fig. 115, B, C). These zoospores develop into new plants 

 (Fig. 115, D, E) as in previous cases. The sexual reproduction 

 presents a high degree of specialization. The male gametes are 



