﻿1903] OOGENESIS IN SAPROLEGNIA 325 



It is the specialization of a periplasm simultaneous with the 

 reduction in the number of functional gamete nuclei that has 

 made possible the elaborately organized oogonium of Perono- 

 spora, Sclerospora, Albugo, Araiospora, and to a lesser degree 

 Pythium. And the coenocentrum is perhaps most largely 

 responsible for the highest specialization. The coenocentrum 

 largely influences and perhaps controls the position and struc- 

 ture of the eggs. The larger the coenocentrum, the more direct 

 is the effect on neighboring nuclei, and the greater is the benefit 

 to such nuclei as are so fortunate as to be within its sphere of opera- 

 tions. So in the struggle for existence among potential gamete 

 nuclei in the oogonium, the coenocentrum has a power of assist- 

 ance that, according to its degree of development, determines 

 the structure of the ^^^^ whether multinucleate or uninucleate. 

 The evolutionary trend is physiologically precisely the same as 

 is shown among the algae (Fucales, Vaucheria), when potential 

 gamete nuclei are sacrificed to provide functional nuclei with a 

 large amount of richly nourished protoplasm. 



But it should be noted that, although the evolutionary pro- 

 cesses in the Peronosporales have resulted in uninucleate eggs, 

 these structures are not strictly homologous with the eggs of 

 algae. They are homologous only in the sense that the eggs of 

 Volvox, Fucus, Vaucheria, Chara, and several other highly 

 developed algae are homologous. In these algae the eggs have 

 an ancestry from much simpler types of gametes, and relation- 

 ships must be traced through these or perhaps through older • 

 forms of asexual spores. The oogonium of the higher Perono- 

 sporales has come through a series of coenogametes of which 

 Albugo Bliti represents a certain stage, but whose earher forms 

 must have been simpler. The primitive conditions probably had 

 a structure comparable to the coenogametes of the 

 and that type of structure finds its nearest approach among the 

 algae in the gametangia that discharge numerous gametes, as 

 illustrated by Cladophora and many of the Siphonales. 



But it will immediately be asked : What are we to do with 

 such algal types as Vaucheria, Sphaeroplea, Oedogonium, etc.? 

 Have they no relation to the fungi? This will be considered 



M 



