314 BOTANICAL GAZETTE. 



cabbages and Cardamine it is less dense. The oospores are not very frequent, 

 considering how common the species is. Although subject to considerable va- 

 riation, the species is comparatively easily recognized by the stout conidio- 

 phores which are abruptly dichotomous above, the divisions being slender and 

 densely ramified. The haustoria are especially large and easily studied. The 

 form on Dentaria from Kentucky corresponds precisely with Rabenhorst's orig- 

 inal specimens of P. Dentarice. 



10. P. Potentill^e De Bary. 



De Bary 1. c. p. 120: Bull. Buss. Inst. 233: Cat. Pacif. Fung. 29. 

 Exs. Ellis N. Am. Fung. 217. 



Conidiophores slender, several times dichotomous, divisions 

 distinctly flexuous. Tips attenuate, approximate in pairs, curved. 

 Conidia violet colored, ellipsoidal, 20-26 p- by 15-19 (i. Oospores 

 yellow, thin-walled, smooth, 22-24 ft in diameter. 



On P. Norvegica. 



Mass. (Farlow), California (Harkness). Europe. 



As far as I am aware the oospores af this species have never been described. 

 I found them on P. Norvegica in October, 1877. The oogonium is very thick- 

 walled and rigid, and is almost completely filled by the oospore, which is al- 

 most exactly spherical and has a thin, smooth wall. In fact, at first sight, one 

 would mistake the oogonium and its contents for a single thick-walled oospore 

 so completely does the oospore fill the oogonium in most cases. In consequence 

 of the structure of the oogonium, the present species must be placed in the same 

 section as P. parasitica if we follow De Bary's classification. The species is 

 common in Massachusetts from June to October. I have no specimens from 

 the Western States, although I have heard that the fungus grows in that region' 



In July, 1882, I found a Peronospora on Geum album at Wood's Holl, Mass., 

 but it was not fully developed, and no oospores were seen. It formed ill-defined 

 spots on the under side of the leaves, which showed a yellowish discoloration 

 on the upper side. I presume that the form on Geum must be included in P. 

 Potentillcr, although the conidiophores were more slender and less branched. At 

 any rate, without more material, I should not venture to separate it as a dis- 

 tinct species. 



11. P. Claytonije n. sp. 



Conidiophores long, naked below, several times dichotomous 

 above, divisions short, flexuous. Tips short, subulate, widely 

 spreading. Conidia broadly obovate, violet-colored, 22-24/7. by 

 15-20/7. Oospores large, 38-45//. in diameter, brown, exospore 

 more or less rugose. 



On Claytonia Virgin int. 



Kentucky. Conim. J. B. Ellis. 



The only specimens of this species which I have seen were those sent by 

 Mr. Ellis. The leaves of the Claytonia were wrinkled and blackened, but no 

 definite spots were found. The conidiophores were rather diffusely scattered, 

 and the oogonia were large and did not contract around the spherical oospores, 



