144 Wisconsin Academy of Sciences, Arts, and Letters. 
With the mildew on these two host plants, a series of infec¬ 
tion experiments was carried on to test their power of passing 
over to and growing upon other grains and grasses. Most of 
the experiments were performed by placing one and one-half 
inch flower pots, containing the seedlings used, under a bell jar. 
The bell jar was left over them from twenty-four to forty-eight 
hours and, in many cases, during the course of the experiment. 
All the seedlings in one half of the pot were inoculated, those 
in the other half serving as controls. An ordinary wooden label 
bearing the name of the plant, the date when the seed was 
planted, and the date of the inoculation, was placed in the pot 
in such a way as to separate the inoculated seedlings from the 
controls. The cereals were grown in the pots used in the ex¬ 
periments. The other grasses were grown in larger pots and a 
few seedlings transferred to the small ones for the experiments. 
Four or five pots, containing usually as many different 
grasses, were placed under the same bell jar. In every experi¬ 
ment, one pot contained uninfected seedlings of the host plant 
used as a source of conidia for inoculation. In this way it was 
always possible to tell whether good, viable spores had been used 
in inoculating the seedlings for, if the conidia infected seedlings 
of their own host plant, their viability was demonstrated. 
For most of the experiments in which rye seedlings were in¬ 
oculated, the Sehlamslead variety of rye was used. In a few 
experiments another variety, the Petkus, was taken. The mil¬ 
dew appeared to infect the two varieties with equal readiness. 
The young seedlings of the cereals appeared in from four to 
six days after sowing the seed. The oat seed was longer in ger¬ 
minating than the others. The grasses came up in from ten 
days to two weeks after the seed was sown. The age of the 
seedlings as stated in the tables is reckoned from the time of 
sowing the seed. In most cases, the first leaf of the seedlings 
of the grains was inoculated, although in older seedlings other 
leaves were also inoculated. 
In some cases, another method of experimentation, suggested 
by Salmon (10) was employed. Green, vigorous leaves of grasses 
or grains were placed on a moist filter paper in a Petri dish. 
Some of the leaves were inoculated, the rest being kept as con- 
