Reed—Infection Experiments. 
143 
more difficult will it be for the specialized form on the one to 
pass over to the other. 
Fifty-five species of grasses have been reported as infected by 
this one mildew, Erysiphe graminis DC (14). In fact all grass 
mildews are included in this one abundant and cosmopolitan spe¬ 
cies. Of this number only sixteen species have been reported in 
this country as being infected with the mildew: Agropyron glau- 
eum (3) (6), A. tenerum (4), Agrostis exarala (3), Arena sp. 
indet. (3), Beckmannia erucaef ormis (3), Bromus unioloides 
(4), B. breviaristatus (4), Elynius condensatus (3), Glyceria 
nervata (3), Hordeum jubatum (3), Poa pratensis (3) (4) (9) 
*(16), P. tenuifolia (3) (6), P. nemoralis (4), P. serotina (4), 
Secale cereale, Triticum vulgare (3). 
This mildew occasionally causes serious damage to forage and 
cereal crops, especially to wheat. Serious outbreaks of the mil¬ 
dew have occurred in Europe on winter sown cereal crops. An¬ 
derson (1), speaking o£ the attacks of the disease in Montana, 
says: “It affects chiefly the Poas and is especially damaging 
to P. tenuifolia, one of the most valued forage grasses.” 
During the last year, I have carried on infection experiments 
using the conidia of Erysiphe graminis from the host plants Poa 
pratensis and Secale cereale. In the latter part of September, 
1903, I brought into the greenhouse several sods of P. pratensis 
infected by the mildew. The grass grew for most of the winter 
but gradually died out. In order to keep a good supply of 
conidia on hand, seed of P. pratensis was sown and the young 
seedlings were placed beside the sods. They became infected 
and served as a source for obtaining conidia for further infec¬ 
tions. In this way, the fungus has been kept growing in the 
greenhouse from the last of September, 1903 to February 1st, 
1905. 
About the last of October, some rye which was growing in the 
greenhouse was discovered to be infected with mildew. This 
mildew was also kept growing in the greenhouse, by the methods 
noted above, from the last of October to the first of July. Dur¬ 
ing the winter, the rye seedlings lived about six weeks and, in 
order to have a supply of conidia, it was necessary to plant seed 
every four or five weeks and inoculate the young seedlings. 
