268 
Journal of Agricultural Research 
Vol. I, No. 3 
While no absolute limits have been established, Table II shows that 
only a very slight germination of spores took place in thermostat VI 
(i i .5 to 12 0 C.) at the end of 24 hours. As the temperature was increased, 
germination became better until the optimum was reached in thermo¬ 
stats X (25.0 0 to 26.0° C.) and XII (35.5 0 to 36.0° C.). Germination 
was somewhat reduced in thermostat XIII (37.4 0 to 37.5 0 C.) and com¬ 
pletely prohibited in thermostat XIV (40.0° to 40.5 0 C.). Of the tem¬ 
peratures tried the minimum for germination would be found in ther¬ 
mostat VI (n.5 0 to 12.0 0 C.), the optimum in thermostats X (25.0 0 to 
26.0° C.) and XII (35.5 0 to 36.0° C.), and the maximum in thermostat 
XIV (40.0° to 40.5 0 C.). 
VIABILITY OP PYCNOSPORES 
Just how long the spores will retain their viability in a dried condition 
is not known. The pycnospores on material collected on August 22, 
1912, and kept in an envelope in the laboratory would not germinate 
in plates of beef agar made on November 27. Hanging-drop cultures 
were made with hydrant water in Van Tieghem cells from the same 
material on December 11, with similarly negative results. On the other 
hand, pure cultures made on August 15, 1912, on corn meal retained 
their viability to June 18, 1913. These results are not directly com¬ 
parable, since there is always a certain amount of moisture present in 
the medium when the culture is started. Furthermore, as was previ¬ 
ously pointed out, this organism produces a considerable amount of 
liquid on corn meal, even though there is no surplus water present in 
the culture when inoculated. 
INFLUENCE OF TEMPERATURE ON GROWTH 
The influence of temperature on the growth of Plenodomus destruens 
in cultures was determined by the use of 10 thermostats ranging in 
average temperatures from 1.09 0 to 37.3 0 C., and in the laboratory 
with an average temperature of 21.9 0 C. These temperatures varied 
somewhat, as will be seen by referring to Table III, where the average 
maximum and minimum temperature for each thermostat is recorded. 
Cultures were made on January 15, 1913, on sterilized rice (1085) in 
test tubes, it having been previously ascertained that this was a favor¬ 
able medium for the growth of the fungus. Five tubes were placed in 
each of the 10 thermostats and one set in the culture room in the labo¬ 
ratory as a check. The cultures were kept in the incubators and under 
observation for 21 days. Table III contains a record of the growth of 
the organism in each thermostat and in the laboratory room on the 
different dates covered by the experiment. 
