Feb. i2,1917 
Studies of the Genus Phytophthora 
235 
As the contributions to the genus in recent years are well reviewed in a 
paper by Guy West Wilson (37), the writer will not attempt to review 
them here. 
EXPERIMENTAL METHODS EMPLOYED 
Pure cultures were obtained from as many of the foregoing species 
and from as many sources as possible. Of the 11 species 1 described, 
nine were studied and grown in pure culture. In addition to these, 
cultures of P. fagi , which is given in Saccardo as a synonym of P. cae - 
torum , were also obtained. It was not possible to procure fresh material 
of P. thalictri or P. colocasiae. The following is a list of the cultures used 
and sources from which they were obtained: 
P. infestans, isolated from potatoes from New York and Maine by the writer, and 
received from G. P. Clinton, Connecticut, I. E. Melhus, Wisconsin, and S. Ito, Japan. 
P. cactorum, isolated by the writer from ginseng from Ohio, Michigan, New York, 
and Pennsylvania, and by D. L. Peters from a species of Phyllocactus in Germany. 
P. phaseoli , isolated by the writer from bean pods from New York, and received 
from G. P. Clinton, Connecticut. 
P . nicotianae, isolated from tobacco in Germany, received from H. H. Whetzel, 
and from tobacco in Japan, received from S. Ito. 
P. syringae, isolated from lilac in Germany, received from H. H. Whetzel, and 
from lilac in Ireland, received from George H. Pethybridge. 
P. arecae , isolated from areca palm in India, received from L. C. Coleman. 
P. parasitica , isolated from castor bean, received from J. F. Dastur, India, and 
G. W. Wilson, New Jersey, the latter culture having probably also come from Dastur. 
P.faberi, isolated from cacao in Trinidad, received from J. B. Rorer. 
P. jairophae , isolated by Jensen in Java from one of the nettles and obtained from 
the Centralstelle fur Pilzkulturen, Amsterdam, Holland. 
P. fagi , isolated by George H. Pethybridge from young plants of Fagus spp. in 
Ireland, and obtained from Centralstelle fur Pilzkulturen, Amsterdam, Holland. 
The study of the cultures was supplemented with a study of herbarium 
material of most of the species. 
The ideal method of procedure would have been to study these forms 
on the original host in each particular case, as in that way no variation 
in size or form could be attributed to an unnatural substrata relationship; 
but when the work was begun this was impossible, because the various 
hosts were not available. The aim was, however, to subject all the 
forms to identical conditions; and with this in view, a number of arti¬ 
ficial media were tried in a preliminary way in order to determine which 
was most favorable for all the forms. 
It was found that the various forms reacted differently on the different 
media both as regards rate of growth and spore forms produced. The 
greater number of species made a good growth and produced an abun¬ 
dance of spore forms on oat agar made, with slight modifications, accord- 
1 Prof. S. Ito recently informed the writer that Mr. K. Sawada, of the Formosa Agricultural Experi¬ 
ment Station, lately described in Japanese two new species of Phytophthora occurring on Allium fistu- 
losum and Solatium melogena, respectively. 
