J2 Nebraska Experiment Station Research Bulletin 22 
tion with an increase in the time interval and that the percentage 
of germination remains small over a period of several weeks. 
Rather peculiar results were obtained at the relative hu- 
midity of 10.5 per cent at all temperatures below 25° C. For 
some unknown reason, a lower percentage of germination was 
obtained at this point than at the relative humidities of 0 and 
21.5 per cent. For example, at 10.5 per cent relative humidity, 
no spores were found capable of germinating after two weeks at 
any temperature, while the number of spores germinating at 
this relative humidity was low in all cases. On the other hand, at 
the relative humidities of 0 and 21.5 per cent a larger number of 
spores germinated over a longer period of time, the percentage 
of germination and the time interval depending somewhat on the 
temperature at which they were held. 
The results of the germination tests show that we have a very 
definite relation between the viability of urediniospores and the 
environmental factors of the temperature and relative humidity. 
No doubt, with the use of a larger number of germination tests 
and more uniformity of rust material, the results could be ex- 
pressed in mathematical ratios. 
Infection tests. — The purpose of checking up the ger- 
mination tests with infection tests was twofold. In the first 
place, it served as a check on the methods used and the re- 
sults obtained with the germination tests. Further, it afforded 
an opportunity to determine whether urediniospores still able 
to germinate were capable of entering the host and producing 
a pustule. 
The results of the infection tests showing the length 
of time, after being submitted to various temperatures and rela- 
tive humidities, that the spores were capable of producing infec- 
tion are given in Table 2. 
As a rule the results of the infection tests are in accord 
with those obtained in the germination tests. In most instances 
where 10 per cent or more of the spores were viable in the 
germination tests, infection was successful. There is also a 
definite relation between the percentage of germination and the 
number of pustules per leaf and number of leaves infected. 
Few or no infections were obtained with any inoculum 
which showed less than 10 per cent germination. Whether this 
was due to the small number of viable spores in the inoculum, or 
whether the spores upon germination were unable to produce 
infection, is not clear. However, it was observed that as the 
