i88 
E. B. MAINS 
ments. Three pots of corn were kept at a temperature averaging 20° C. 
and three at a temperature averaging 13° C. The incubation period 
of the rust at 20° C. was 7 days while that at 13° C. had an incubation 
period of 13 days, showing that low temperatures retard the develop- 
ment of Puccinia Sorghi in its host. 
Experiment 4. — Six pots of corn were inoculated with uredospores 
of Puccinia Sorghi and kept under a bell jar at a temperature of 18° C. 
for 12 hours. Two of the pots were placed under bell jars in an Eberbach 
electric incubator at 40° C. The outer door of the incubator was left 
open, allowing light to enter, and the incubator was placed in an east 
window. In a similar manner two pots were kept in an incubator at 
30° C. Even with the outer doors open these incubators maintained 
a temperature varying only a few degrees. The other two pots of 
corn were placed under belljars in a box about the size of the incubators 
with the open side facing the window. These two pots were at room 
temperature, which according to a thermograph averaged 18° C. The 
belljars were removed once a day from all the plants in order to renew 
the oxygen supply. 
At the end of the fourth day, the two pots of corn at 40° C. were 
dead. Pustules appeared on the plants at 18° C. in seven days. 
The only sign of rust on those at 30° C. at this time was the greenish 
spots mentioned before as remaining in infected areas when the rest 
of the leaf is yellowing. Sections through these areas showed a my- 
celium which was only sparingly developed. At the end of fourteen 
days, no pustules had formed on the plants at 30° C. At this time, 
most of the leaves were dead, only the upper still retaining a green 
appearance. 
These results show that a temperature of 30° C. or higher prevents 
the development of Puccinia Sorghi in its host. 
Effect of Humidity upon Development 
The work, as far as carried out, was done with Puccinia Sorghi. 
Experiment 5. — Fourteen plants of maize were inoculated with the 
uredospores of Puccinia Sorghi and kept under belljars at 18° C. for 
twelve hours. Four plants were then placed in a south window under 
belljars, by which means they were kept in a nearly saturated atmos- 
phere. The remaining ten plants were placed without belljars on the 
table beside the other four. The earth in the pots of five of these ten 
