Wilson: Studies in North American Peronosporales 207 
from Fragaria vesca in France. This is a very large species, the 
conidiophores reaching the rather startling height of a millimeter, 
and branching more profusely than do those of other species on 
Rosaceous hosts. The conidia, as might be expected, average a 
little larger also. As the leaves of Fragaria and certain species 
of Potentilla which are infected with the fungus are not suffi- 
ciently different either in texture or hairiness to account for the 
wide variation between the fungi on them we are led to conclude 
that they represent two valid species. 
The third species with which we are concerned, P. Rubi Rab . 15 
was distributed by Rabenhorst on Rubus fruticosus from Ger- 
many. In the Rubus- inhabiting fungus the conidia and conidi- 
ophores are nearer the same size as those of P. Potentillae than 
is the case with P. Fragariae. However, the two species, similar 
as they are, are quite readily distinguishable.. P. Rubi has conidi- 
ophores more branched, with longer ultimate branchlets, and a 
denser head, while the conidia are somewhat broader and darker 
in color than those of P. Potentillae. 
From the foregoing comparison we conclude that there are in 
America three species of Peronospora on Rosaceous hosts. These 
are P. Rubi Rab. confined to the shrubby genus Rubus, P. Frag- 
ariae Roze & Cornu, collected in Iowa on Fragaria, and P. Poten- 
tillae De Bary on various species of Agritnonia, Geum, and Potcn- 
tilla. Besides these P. sparsa Berk, is found occasionally on 
Rosa. 
Peronospora Arthuri Farlow, Bot. Gaz. 8: 315. 1883 
This species, which appears to be rather widespread and some- 
what sporadic in its appearance, presents an interesting puzzle to 
those who follow Schroter and Fischer in dividing the species of 
Peronospora into two groups on the basis of oospore markings, 
placing in Calotheca all those species which have reticulate or 
tuberculate oospores and in Leiotheca those having smooth or 
wrinkled oospores. In the present species the oospores possess 
pronounced characters of both these groups, as the epispore is con- 
spicuously wrinkled, and thickly covered with short blunt tubercles. 
15 Fungi Europ. 2676 (hyponym) 1881. — Schrot. in Cohn, Krypt. FI. Schles. 
31 : 250. 1886. 
