42 2 BOTANICAL GAZETTE [December 



dense cytoplasm in the center of the oogonium, differentiated 

 into two portions of varying density. In history and structure 

 the coenocentrum agrees well with that of A. Blid, with the 

 exception that the central globule has not yet been demon- 

 strated. 



In function the coenocentrum serves to attract and to retain 

 the female pronucleus, as in A. Tragopogonis and A. caiidida 

 (Stevens 'oi), and in Pero?iospora parasitica (Wager 'oo). No 

 evidence of nutritive function was apparent as in the case of the 

 forms of Albugo just mentioned. 



The mitosis in Sclerospora is in general of the type described 

 for A, Bliti (Stevens '99). The spindle is intranuclear, the mem- 

 brane persisting until metasphase. No centrosomes or polar 

 radiations were seen. Chromosomes were not counted with 

 accuracy, but they are few in number, probably four. 



The antheridium in Sclerospora is usually very small, and is 

 closely appressed to the oogonial wall {Jig- 4)^ Usually it is 

 impossible to distinguish the antheridial wall from the oogonial^ 

 and very frequently the thinning of the oogonial wall gives the 

 antheridium the appearance of being imbedded in it. The 

 antheridial nuclei enlarge simultaneously with those of the 

 oogonium, and undergo mitosis. No receptive papilla was seen^ 

 and this peculiar structure may be lacking in the genus. 



Communication is opened between the antheridium and the 

 oogonium by the bulging and eventual rupturing of the oogonial 

 wall at the thin point between these organs. The edges of the 

 ruptured wall thus extend inward. The antheridial tube, which 

 is soft and gelatinous, penetrates the oosphere, discharging its 

 contents before it reaches the center {^fig. 4). The track of the 

 antheridial tube remains in evidence for some time as a denser 

 region in the cytoplasm. 



The male pronucleus is slightly smaller than the female and 

 is more ovoid in form (Jig, y). It migrates to the female and 

 fuses with it, but the fusion was not studied critically owing to 

 the smallness of the nuclei. 



The oogonial wall, as stated above, is much thickened even 

 in the youngest oogonia, and it does not change in dimensions 



