Wilson: Studies in North American Peronosporales 203 
that the fungus is similar to Botrytis parasitica. It would appear 
that he had a species of Peronospora, but it is impossible to say 
which one without seeing material of his collection. In the 
course of his remarks he refers to the remarkable phenomenon of 
the same plants also harboring a species of Erysiphe, and, to judge 
from the comments of his contemporaries, the material which he 
disturbed among them contained only the later fungus. 
In 1863 Fuckel issued in his Fungi Rhen. 40 a Peronospora on 
Euphorbia platyphylla, naming it P. Euphorbiae, and in his mono- 
graph of the same year De Bary described another species from 
Euphorbia Syparissias as P. Cyparissiae. 10 Through the kindness 
of Doctor Tranzschel it has been possible to examine material 
from Fuckel’s exsiccati. A comparison of this with authentic 
material of P. Cyparissiae shows them to be distinct from each 
other as well as from the species to be mentioned later. P. Eu- 
phorbiae has hyaline conidia, while P. Cyparissiae has violet ones. 
P. Euporbiae has slender conidiophores which are 6-8 times 
branches, the ultimate branchlets rather widely divergent, the 
branches straightish, and forming a rather close head. P. Cypar- 
issiae has a stouter conidiophore with more erect habit, and a 
closer head, the ultimate branchlets also widely divergent. As 
the oospores of P. Cpyarissiae are unknown no comparison on 
this point can be made. 
. The next species to be described was P. andina Speg. 11 from 
Argentina, which is much smaller than the preceding. The coni- 
diophores are rather small, branching 3-5 times, the branches 
spreading, the ultimate branchlets rather flexuose, and forming an 
open head. The conidia are hyaline. The oospores are unknown. 
The North American species of Peronospora on hosts of this 
family has been variously recorded as P. Euphorbiae and P. 
Cyparissiae. A close study of the American fungus and a com- 
parison with these European species shows it to differ in' several 
respects from either of them. As our species has violet conidia 
we can dismiss P. Euphorbiae with the remark that its oospores 
are more wrinkled than those of our species. Its conidia, while 
of the same color as those of P. Cyparissiae are slightly more 
10 Ann. Sci. Nat. IV. 20: 124. . 
11 Ann. Mus. Nac. Buenos Aires III. 12: 282. f. 3 . 1909. 
