430 
Journal of Agricultural Research 
Vol. XXIX, No. 9 
graphs shows the temperature in 
degrees centigrade; the perpendicular 
shows the diameter of the mycelial 
disks. The first graph shows the 
diameter of the mycelial disks at differ¬ 
ent temperatures at the end of 2 days, 
while the other graphs show their 
comparative diameters after 4, 6, 8, 
10, and 15 days, respectively. 
same throughout the experiment. No 
growth took place at 30.5° during 
the first two days, although ia fair 
growth was made at 30°. There was 
some visible growth in four days at 
33.5°, but none until the eighth day 
at the maximum temperature, at 
which a visible growth took place (36°). 
There was no growth even after 15 
T£MP£&?TZ//Z£: °C. 
O S /O /& 20 25 30 35 40 4# 
Fig 1 —Curve showing the time in hours required for the spores to produce germ tubes equal in 
length to the diameter of the spores when incubated in sweet-potato decoction at different tem¬ 
peratures 
No sharp optimum was noticeable 
for the first four days, but it became 
more pronounced thereafter. The.op¬ 
timum temperature tried was 26.8° C., 
although growth was only slightly less 
rapid at 22.5°, the next lower tempera¬ 
ture. Above 26.8° the growth rate 
dropped abruptly. The optimum for 
mycelial growth lies somewhere be¬ 
tween 25° and 27°, which is several de¬ 
grees lower than that for spore germi¬ 
nation. The optimum remained the 
days at 38°, but a fair growth was 
made at 36°. Weimer and Harter (18) 
found that the more rapid-growing 
species of Rhizopus reached the highest 
thermal point of growth in the first 24 
hours. Edson and Shapovalov (6) also 
found this to be the case with the 
fungi which they studied. However, as 
already pointed out, the brownrot 
fungus did not make a measurable 
amount of growth at the maximum 
temperature for several days. Never- 
