DEVELOPMENT OF PLANTS 



187 



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 

 usually formed in pairs in small cells and are similar to but 

 smaller than the zoospores, while the female gametes are de- 

 veloped singly in the ordinary cells of a filament which become 

 greatly enlarged and spherical or ovoid in form (Fig. 116, A, B). 

 The female gamete is motionless but the colorless region on one 

 side of the gamete certainly suggests the idea that this body is 

 related to the zoospores and male gametes, but that it has lost 



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. 



its cilia. At maturity, openings of various kinds appear in the 

 oogonium through which the male gametes enter and one fuses 

 with the female (Fig. 116, A, 0). The thick-walled gametospore 

 that results from this union is set free by the decay of the oogonial 



