﻿1903] OOGENESIS IN SAPROLEGNIA 335 



etc.) that presents to the writer's mind conditions most nearly 

 like the ancestry of the Mucorales, Saprolegniales, and Pcrono- 

 sporales, that is, an ancestry whose sexual organs were cocnoga- 

 metes. Perhaps, however, further studies on the oogonium of 

 Vauchcria may bring this structure into harmony with coenoga- 

 metes. 



The coenogamete among the fungi must have come through 

 the homologous structure among the algae, the gametangium. 

 We cannot suppose that such gametangia w'ere highly specialized. 

 It is hardly possible that they were heterogamous, for a highly 

 differentiated oogonium wQuld not be likely to return to condi- 

 tions as simple as the primitive coenogamete. The gametangia 

 of such isogamous algae as Cladophora and Codium present 

 most nearly the structure demanded of the progenitors of the 

 primitive coenogamete, but, of course, these forms are mentioned 

 only as illustrations of conditions undoubtedly present in many 

 groups of algae at various periods in their evolutionary history. 



We can only speculate as to the manner in which a game- 

 tangium might become a coenogamete. The writer has already 

 offered some suggestions on this point (Davis, 1900, p. 308), 

 and he is more inclined to- them since the recent studies of 

 Harper (1900) and Stevens (1901) and the present investiga- 

 tion of Saprolegnia. We can readily conceive the derivation 

 from isogamous algae of groups of aquatic fungi with terminal 

 sporangia discharging motile gametes after the manner of Cla- 

 dophora. Should such fungi leave the water and adopt terres- 

 trial habits either as saprophytes (Mucorales) or as parasites 

 (Peronosporales), certain changes in the sexual processes would 

 be very likely to result. The gametangia could not form and 

 discharge motile gametes excepting when wet, and would be 

 ■compelled to adapt themselves to the aerial environment. They 

 would be very likely to develop such unity of structure and 

 behavior as is displayed in Pythium and Peronospora by those 

 sporangia (conidia) which have given up the habit of forming 

 -zoospores and now germinate by a tube. The gametangium would 

 become a coenocytic unit, with the chemotactic qualities and pos- 

 sibilities associated with sexuality. These chemotactic influences 



