146 Wisconsin Academy of Sciences x , Arts, and Letters. 
died, turning yellow. The cells in the infected areas of the 
rye leaf retained their green color for a longer time than the 
others. The fungus seemed to act upon the infected cells in such 
a way as to prolong their life. On the other hand the cells in 
the infected region of the leaves of the blue grass died first, the 
leaves turning yellow there, while the uninfected parts often 
remained green for several days afterward. 
My first experiments were aimed to show the possibility of 
readily infecting leaves and seedlings of blue grass with conidia 
from the same host. The first five or six experiments failed. 
This was doubtless due to the fact that the spores used were 
either weak or dead. They were taken from the plants which 
had just been brought into the greenhouse and it was evident 
that conidia were not produced at all abundantly until after the 
plants had been m the greenhouse about three weeks. The 
mildew seemed to be brought to a standstill by the change to the 
greenhouse, not growing vigorously for some time. Later an 
abundance of conidia w r as produced on the infected grass and I 
then had no more trouble in transferring the mildew. After 
these first failures, forty-one additional experiments were per¬ 
formed in which the blue grass was inoculated with conidia 
from the same host and only three were unsuccessful. 
A series of observations was next made to determine to what 
extent the mildew on the rye and blue grass had become special¬ 
ized. Spores from both of these host plants were sown on leaves 
and seedlings of various grasses which are reported as hosts of 
Erysiphe graminis. 
I have used for the most part grasses that are commonly cul¬ 
tivated and must hence have been repeatedly exposed in nature 
to infection from both rye and blue grass. Considerable diffi¬ 
culty was experienced in obtaining seed of many species of 
grasses. Seed of Glyceria fluitans was obtained from Currie 
Bros., Milwaukee, Wis.; seed of Bromus mollis from Vaughn’s 
Seed Store, Chicago, Ill.; seed of Lolium perenne, Festuca 
elatior, Daciylis glomerata and Poa nemoralis from J. M. Thor- 
bum & Co., New York; seed of Poa compressa, Phleum pratense 
and Festuca heterophylla from Peter Henderson & Co., New 
York; seed of Poa trivialis from the Bureau of Plant Industry, 
