1891.] Notes upon Peronosporece. 339 



white felt and developed a premature reddening of the affected 

 foliage. In midsummer it disappeared only to appear again 

 upon the seedling plants in autumn ready for its hibernation 

 in the substance of its hosts. It was taken also upon G. mac- 

 ulatum but not upon G. Robcrtianum. 



B RE MIA Lactuc.e Reg. has only been met with upon gar- 

 den lettuce and principally in green-houses where it did some 



damage. 



PERONOSPORA PARASITICA D. By. is one of the most wide- 

 spread and common of all the mildews. It has been observed 

 on nearly all the ordinary hosts, as Cardamine hirsuta and 

 C. laciniata in early spring, and radish and cabbage later in 

 the season. A new host apparently in Alyssum maritimum 

 was found affected, growing in a green-house with radishes 

 near by, likewise infested. The CrucifercX in general are subject 

 to the attacks of this mildew. 



PERONOSPORA CUBKNSIS B. & C has been the most in- 

 teresting species this season. It will be recalled that this 

 mildew, in the spring of 1889, was known only in Japan, Cuba 

 and this state. During that year it was found in the southern 

 states. Last year it was only rarely met with, but almost 

 daily looked for. Until midsummer of the present season it 

 had not been found, but since then it has appeared, literally 

 almost everywhere in this region, and through correspondence 

 it is learned that it is very wide spread and general. From 

 Professor Galloway I learn that it is abundant in Washington, 

 and Dr. Sturgis sent specimens from New Haven, where it 

 was common upon watermelon. Upon the same host it 

 seems accountable for the failure of the crop to some extent 

 in this vicinity. No oospores have been met with, but the 

 rapid germination of the violet conidia by zoospores is easily 

 demonstrated. The wild species of Cucurbitaceae, namely, 

 Sicyos angulata and Echinocystis lobata, have been examined 

 with the hope of finding the mildew, but without success. 



PERONOSPORA EFFUSA Rabh. has been much more abund- 

 ant this season than formerly. The crop of spinach now 

 standing in some places is badly spotted with the mildew, 



which will materially shorten the crop. 



PERONOSPORA POTENTILI ,.i: D. By. has been taken occa- 

 sionally upon the common host 

 most interest is the finding of it upon P. grandifi 



No 



