PERONOSPORALES 191 



bordering the ooplasm. A section through the oogonium at 

 this stage shows the vacuoUite periplasm at the periphery, a circle 

 of nuclei next within in the later stages of mitosis, and at the 

 center the sphere of homogeneous ooplasm. Stevens calls this 

 the stage of zonation. The division figures of certain of the 

 nuclei in this division lie across the hne of demarcation between 

 the periplasm and the ooplasm, and in the completion of these 

 divisions, one daughter nucleus in each case enters the ooplasm. 

 Thus approximately fifty nuclei enter the oosphere. It becomes 

 consequently a coenocytic structure and is termed by Stevens 

 the compound oosphere. The nuclei in the antheridium divide 

 simultaneously with those in the oogonium, resulting there in 

 about seventy at this stage. The receptive papilla ruptures or 

 is withdrawn, and the fertihzation tube enters the oogonium 

 and penetrates to the oosphere. A relatively small and incon- 

 spicuous coenocentrum is developed, but fails to function in 

 attracting the sex nuclei, and disappears before fertilization 

 occurs. A second division of all the nuclei in the antheridium 

 and oosphere now takes place. Those in the periplasm fail to 

 divide and soon disintegrate. This division results in the 

 presence of about one hundred nuclei in the oosphere and one 

 hundred and forty in the antheridium. The fertihzation tube 

 then ruptures, and the majority of the antheridial nuclei pass 

 into the oosphere where the male and female nuclei fuse in pairs, 

 approximately one hundred fusion nuclei resulting. The super- 

 numerary male nuclei disintegrate, and the oospore wall is 

 formed, the epispore being strongly reticulate. The multi- 

 nucleate oospore then hibernates, the fusion nuclei passing the 

 winter without change. 



Reviewing the situation we see that in A. Candida a single 

 male nucleus fuses with a single female nucleus in a uninucleate 

 oosphere, the receptive papilla is small, the coenocentrum is 

 highly developed, the fusion nucleus divides rapidly to form 

 about thirty nuclei before hibernation, and the epispore is tuber- 

 culate. In A. bliti many male nuclei fuse in pairs with female 

 nuclei in a multinucleate oosphere, the receptive papilla is long 

 and prominent, the coenocentrum is relatively inconspicuous 

 and functionless, the fusion nuclei do not divide before the period 

 of rest, and the epispore is reticulate. 



The sexual process in A. portulacae is very similar to that in 

 A. bliti, while that in A. lepigoni (Ruhland, 1903) is practically 



