PHYCOMYCETES 31 



the oosphere. It is unique also in that the terms oosphere and 

 female gamete may be apphed here with complete justification 

 to the same body. 



In many other genera of the Phycomycetcs fertilization is 

 immediately preceded or accompanied by a differentiation of 

 the contents of the female gametangium to form one or more 

 spherical masses of protoplasm. Though these are commonly 

 called oospheres they are not completely homologous with the 

 oosphere of Monohlepharis, since they are in the beginning 

 multinucleate. Phycomycetes having oospheres of this sort 

 include such genera as Achlya, Didyuchus, Pythium, Albugo, 

 and Peronospora. In no case of this type does the male game- 

 tangium form antherozoids. Instead it pushes out a branch, 

 called the fertilization tube, which pierces the wall of the female 

 gametangium and penetrates to the oosphere before rupturing 

 and discharging a part or all of its contents. When the oogonium 

 contains several oospheres the tube branches, or several anther- 

 idia may send tubes into a single oogonium. In all such cases 

 the male and female gametangia are both plurinucleate from the 

 first. In the more primitive genera (e.g., Achlya and Didyuchus) 

 the entire content of the oogonium is used in the formation 

 of the oospheres, whether there be one or more. In higher 

 forms (e.g., Albugo, Pythium, Araiospora, and Peronospora) 

 differentiation of the protoplasm into periplasm and ooplasm 

 occurs, and only the ooplasm is incorporated in the single 

 oosphere formed in these genera. The oosphere in the begin- 

 ning is plurinucleate. Later it usually becomes uninucleate, 

 through disintegration of the extra (supernumerary) nuclei, 

 before fertilization occurs. In a few species (e.g., Albugo bliii) 

 the oosphere remains plurinucleate and, when fully formed, is 

 fertilized by a number of male nuclei which are discharged 

 from the fertihzation tube and fuse in pairs with the female 

 nuclei. Even in the forms in which the plurinucleate oosphere 

 becomes uninucleate before fertihzation the body may not be 

 correctly termed a gamete except with respect to function since 

 in the morphological and phylogenetic senses several potential 

 gametes contribute to the formation of each oosphere. In 

 species in which the oosphere remains plurinucleate to maturity 

 the terms compound oosphere and coenogamete have been 

 applied by various authors. To the student of comparative 

 morphology the latter name seems especially unfortunate. The 



