160 Wisconsin Academy of Sciences, Arts, and Letters. 
In connection with these experiments the seedlings of rye 
that were inoculated with conidia from rye uniformly became 
infected. The same was also true in the case of the experi¬ 
ments in which blue grass was inoculated with conidia from 
blue grass, no infection occurring in only one case. The con¬ 
trols in every case were free from mildew when the inoculated 
seedlings became infected except in experiments 87 and 89 
where some of the controls near the inoculated leaves had small 
infected areas on them. In the case of the rye many of the con¬ 
trols in several experiments when examined eight to ten days 
after the inoculations were made had numerous small infected 
areas on them. This was doubtless due to some of the spores 
that were formed on the infected leaves falling upon the con¬ 
trols. The inoculated seedlings also had several additional in¬ 
fected areas on them when the infection of the controls was ob¬ 
served. 
These experiments confirm the general conclusion that spores 
of the mildew from one grass will not infect a grass belonging 
to a different genus. Marclial, it. is true, states that the form 
on oats is the same as that on Arrhenatherum elatius. Salmon, 
however, was unable to verify this statement. 
It is entirely possible that for E. graminis at least, there is 
one, if not more, distinct physiological species for each genus of 
grasses that contains species which are hosts for this mildew. 
In many genera of grasses the specialization has undoubtedly 
gone still further so that there may be a number of physiolog¬ 
ical forms upon the various species of the same genus. This is 
Salmon’s conclusion in the case of the Brome grasses and my 
work with the various Poas leads me to the conclusion that there 
is more than one at least partially differentiated physiological 
form for this genus also. 
Further investigations will probably show that some physio¬ 
logical forms are much more fixed in their characters than oth¬ 
ers, just as is the case with morphological species. Such special 
forms will doubtless be found to grade over into each other and 
we may thus get interesting evidence as to their developmental 
history. 
