808 
Journal of Agricultural Research 
Vol. XXXI, No. 9 
there was a gradual increase in growth from the minimum tempera¬ 
ture to the optimum, then a more rapid decrease as the maximum 
temperature was approached. A temperature of 36° C. was avail¬ 
able in only the first four experiments, but growth of all cultures kept 
at tliis temperature in these experiments was entirely checked. The 
lowest temperature employed was 4° C., at which growth was ex¬ 
ceedingly slight. Measurements of diameter of colonies of the differ¬ 
ent strains grown at the different temperatures are given in Table I 
and the averages are shown graphically in Figure 3. 
Table I .—Effects of air temperatures on the growth of the mycelium of three strains 
of Ophiobolus graminis on potato-dextrose agar, as shown by measurements of 
diameter of colonies 
Strain of fungus 
Oregon 
Average 
New York __ 
Average 
Arkansas_ 
Average 
Diameter of colonies grown at the different temperatures 
h *. 
o 
p 
7 ° C . 
9 ° C . 
10 ° c. 
15 ° C . 
19 ° C . 
& 
o 
p 
24 ° C . 
28 ° C . 
Q 
O 
CO 
33° C. 
Cm. 
0.5 
.5 
.5 
Cm. 
0.5 
.5 
.5 
Cm. 
2.0 
2.0 
1.5 
Cm. 
2.0 
2.0 
1.5 
Cm. 
6.5 
7.0 
7.0 
6.5 
Cm. 
6.0 
6.0 
6.0 
6.0 
Cm. 
9.0 
9.0 
9.0 
9.0 
Cm. 
9.0 
9.0 
9.0 
9.0 
Cm. 
Cm. 
2.5 
2.5 
4.0 
4.5 
Cm. 
1.0 
— 
. 
.5 
.5 
1.8 
1.8 
6.8 
6.0 
9.0 
9.0 
3.4 
1.0 
.5 
.5 
.5 
1.0 
1.0 
.5 
1.5 
1.5 
1.0 
2.0 
2.0 
1.5 
8.0 
8.0 
8.0 
7.0 
9.0 
9.0 
9.0 
9.0 
9.0 
9.0 
9.0 
9.0 
9.0 
9.0 
9.0 
9.0 
6.5 
4.0 
3.5 
2.5 
2.5 
2.5 
2.0 
.5 
.5 
1.0 
.5 
.8 
1.3 | 
1.8 
7.8 
9.0 
9.0 
9.0 
4.7 
2.4 
.7 
.5 
.5 
.5 
1.0 
1.0 
1.0 
1.0 
1.0 
1.0 
2.0 
2.0 
2.0 
5.0 
5.0 
4.0 
4.0 
8.0 
8.0 
8.0 
8.0 
9.0 
9.0 
9.0 
9.0 
9.0 
9.0 
9.0 
9.0 
4.0 
4.5 
2.0 
2.0 
.5 
.5 
1.0 
1.0 
1.0 
.5 
.5 
1.0 
1.0 
2.0 
4.5 
8.0 
9.0 
9.0 
4.3 
!. 3 
.9 
A typical complete series of cultures is shown in Plate 3. It is 
evident that Ophiobolus graminis will grow at temperatures ranging 
from 4° to 33 d C., with a maximum growth at 23° to 24°. This 
range of temperature for the growth of the fungus is almost as wide 
as the range for growth of the wheat plant, and even though wheat 
will grow at a Sightly higher temperature, it can not be grown 
economically under such conditions. The optimum temperatures 
for the growth of both are about the same, as shown by McKinney 
and the writer (11) but it can not be assumed from this that the 
fungus is most destructive to wheat plants at those temperatures. 
INFLUENCE OF HYDROGEN-ION CONCENTRATION ON GROWTH 
OF THE FUNGUS 
Growth for the three strains of the organism as related to hydrogen- 
ion concentration was studied in potato-dextrose agar, nutrient 
broth, and Czapek’s full nutrient solution. In the solid medium, 
growth rates were determined by measuring the diameter of the 
colonies. In the liquid media, the dry-weight method was used. 
The hydrogen-ion concentrations of the media were determined by 
the Clark and Lubs (2) colorimetric method. The determinations 
were made at room temperature, following adjustment of the media 
to a desired reaction, and such values represent the initial hydrogen- 
