92 BOTANICAL GAZETTE [AUGUST 
nium in Vaucheria tends to bring the Saprolegniales into a somewhat 
close relationship to Vaucheria, not directly of course, but probably 
through more generalized types of the Siphonales now extinct. 
The Peronosporales offer a more difficult problem than the Sap- 
rolegniales, yet there are fundamental features of oogonesis here in 
agreement with this group and with Vaucheria, namely a multi- 
_ nucleate oogonium and extensive nuclear degeneration. The advance 
of the process of oogenesis in the Peronosporales over that of Vaucheria 
lies in the differentiation of ooplasm and periplasm, the first being 
associated with a remarkably well-developed coenocentrum. The 
influence of this coenocentrum determines the survival of one or more 
nuclei in the ooplasm to give a uninucleate or multinucleate egg. The 
periplasm, containing numerous nuclei, becomes separated from the 
ooplasm, and although assisting in the deposition of the oospore 
wall its nuclei and cytoplasm finally become disorganized. 
The processes of oogenesis in the Saprolegniales and Perono- 
sporales seem higher than those of Vaucheria because of the remark- 
able activities of the coenocentra. But to derive the sexual organs 
of the first two groups from the last form, it would be necessary to 
postulate the suppression of two important activities in Vaucheria, 
namely, the development of motile sperms and the formation of pores 
in the gametangia for the entrance and exit of these structures. The 
suppression of the pore formation and consequent modification of 
the sexual cells, the establishment of several coenocentra in the 5ap- 
rolegniales, and the specialization of a periplasm in the Perono- 
sporales are peculiarities involving very important protoplasmic 
activities not represented in Vaucheria. ; 
We have in the Saprolegniales and Peronosporales the interesting 
association of complex female organs developing eggs, with 
organs that are much simpler. The antheridia in the first iwe 
groups are all mutinucleate and morphologically gametangia. 
certain forms (Albugo Bliti and A. Portulacae) the antheridia 4 
because 
