32 THE LOWER FUNGI— PHYCOMYCETES 



nuclei which fuse here are clearly in their homologies the gametic 

 nuclei, and it may well be said that here fusion of undifferenti- 

 ated gametes occurs. The oosphere in such cases is thus not 

 comparable morphologically to the gamete in Monohlepharis 

 but is instead an aggregation of non-individualized gametes 

 functioning in its entirety as a single gamete. 



The same situation exists in the case of the antheridium. In 

 species in which the oosphere remains plurinucleate to maturity 

 numerous antheridial nuclei function. In species in which the 

 mature oosphere is uninucleate conditions are various. In some 

 cases only a single male nucleus passes through the fertilization 

 tube. In others supernumerary antheridial nuclei enter the 

 oosphere, and, on failing to find mates, disintegrate. In some 

 of the higher genera (Peronosporales) the content of the anther- 

 idium is differentiated into a central mass of functional gonoplasm 

 which passes through the tube, and a layer of periplasm which 

 remains in the antheridium. In these various cases, the anther- 

 idial nuclei, whether functional or not, are termed gametes or 

 gametic nuclei by many writers. The term coenogamete is 

 used by other authors, and is applied to the content of the anther- 

 idium considered as a unit. After fertilization has been effected, 

 the antheridium tends to collapse, and is of no further significance 

 in the Ufe cycle. Meanwhile in the oogonium, the oosphere 

 assumes a wall, and thereby becomes the oospore. The oospore 

 functions as a resting spore, and finally germinates to form the 

 thallus of the succeeding generation. 



The fungi which form oospheres were called Oomycetes (egg- 

 forming moulds) by early students. The name has persisted, 

 and, in most modern classifications, is appHed to one of 

 the primary subdivisions of the Phycomycetes. The type of 

 sexual reproduction characterized by oosphere formation is 

 termed oomycetous. The term oospore is used correctly only 

 for the spore which results directly from the maturation of the 

 oosphere. 



Though the delimitation of the oosphere and its transforma- 

 tion into the oospore are the most essential characteristics of 

 oomycetous reproduction several other features of this type of 

 sexuality are commonly present and should be indicated. The 

 sexual identity of the male and female gametangia is evident. 

 They differ in size and shape, the female being the larger and 

 typically the more nearly globose. They differ also in function, 



