1902] STUDIES IN THE FERTILIZATION OF PHYCOMYCETES 423 



as it matures. With zonation the regions of ooplasm and peri- 

 plasm are clearly mapped [fig^ j)^ and with the opening of the 

 antheridial tube the plasmoderma appears. The oospore wall 

 now develops rapidly, first appearing as a clear!}' defined wall 

 {fig- 5) J then rapidl}^ increasing in thickness {Jig, 6), As the 

 oospore wall thickens the oogonial wall collapses in irregular 

 folds [fig. 6), and the periplasm and periplasmic nuclei degene- 

 rate. The protection afforded by these two thick walls appears 

 to hinder seriously the penetration of killing and fixing fluids or 

 subsequent manipulation, and no good preparations showing 

 nuclei were obtained at any stage after the second wall was far 

 developed. 



GENERAL CONSIDERATIONS. 



The general bearing of the cytological evidence on the rela- 

 tionship of Sclerospora is to emphasize its affinity to the Peron- 

 osporaceae rather than to the Albuginaceae, and to indicate its 

 specialized rather than primitive character. The general course of 

 development of both antheridium and oogonium, and the behavior 

 of the periplasm are as in the whole group Peronosporales, The 

 mitosis in both of these organs has been shown by Trow 

 ('99) '01), Hartog ('95), Wager (^96, '00), Miyake ('01), Stevens 

 ('99, '01), King ('02), and others, to be characteristic of both 



Saprolegniales and Pernosporales. 



. The mode of zonation in Sclerospora is not that of the Sapro- 

 legniales (Trow 'or, Miyake '01, Hartog'95), nor of theprimitive 

 Albuginaceae (Stevens '99). It does agree closely, however, 

 with the Peronosporaceae. While the zonation of A.ca/fdida2Lgrces 

 with that of the Peronosporaceae, Sclerospora shows by the nature 

 of its coenocentrum, which in structure, history, and function is 

 clearly like that found in Peronospora, its closer relationship to 

 the Peronosporaceae than to any Albugo." 



The conclusion regarding the relationship of the genus, purely 

 from cytological standpoint, coincides with that drawn from the 

 gross study of asexual spore-bearing organs, and emphasizes the 

 relationship of this genus to Peronospora, of which genus it was 



once considered a "member. 



Sclerospora, as shown by the combined evidence of the 



