-Conidiophores, but in other respects they are quite similar. 
Witson : NorTH AMERICAN PERONOSPORALES 389 
Conidiophores Berpy, aa Dake freely branching ; odspores free 
from the walls o ogon 
Branches of the fee ea apically obtuse. 4. Rhysoth 
Branches of the conidiophore apically acute. 5. SEEN 
“ove gem dichotomously branched, the branches arising at right angles to the 
n axis, successively shorter; conidia germinating by a germ-tube. 
PERONOSPOREAF. 
1. PHYTOPHTHORA de Bary, Jour. Roy. Agr. Soc. 
England II. 12: 240. 1876 
Mycelium much-branched, hyaline; conidiophores arising 
singly or in groups from the stomata, or breaking through the 
epidermis, branched or apparently simple, with irregular thicken- 
ings below the conidia, which are borne apically in a scorpoid 
cyme ; conidia oval, papillate ; zoospores oval, biciliate, escaping 
by the rupture of the papilla ; oospores intramycelial, the epispore 
more or less ridge 
Type species, Peronospora infestans Casp. 
Herbarium material of the species of this genus is very unsatis- 
factory for study, as the conidiophores form a very dense covering 
to the host, and being quite flaccid and often very long they form 
at maturity a dense felt in which the individual conidiophores are 
effectively obscured. This is especially true of P. infestans, while 
Some of the foreign species are not difficult to study. 
Key to the species 
Conidia usually only one, rarely two, borne at the apex of an aborted cyme; conidio- 
phore simple or branched below. 
Host Fabaceae. 1. P. Phaseoli. 
2. P. Colocasiae. 
Conidia numerous in a simple or compound 
Conidia sessile or long-stalked in a shple cyme. 
3. P. Nicottanae. 
onidia large, 50u, or more. 4. #. Coctarnce: 
Conidia sessile in a compound cyme. 
ost Solanaceae 
Host Ranunculaceae. 
5. P. infestans. 
6. P. Thalictri. 
I. Pay a PuasEott Thaxter, Bot. Gaz. 
14: 274. 1889 
The present species differs rather markedly from the other 
American species of the genus in the method of branching of the 
The 
Conidiophores are very long, simple, or more commonly branched 
