Apr. 7 .1923 
Temperature Relations of Eleven Species of Rhizopus 19 
try a temperature between 7.4° and 1.5°, but it is quite probable that 
growth will take place below 7.4° if sufficient time is allowed, since the 
spores germinated at 1.5°. Growth by tritici, nigricans, and nodosus at 
b.5® began after 12, 8, and 10 days, respectively. These fungi also made 
some growth at 6° to 8° in Hanzawa's experiments. Microsporus and 
refiexus are the lowest temperature forms so far as growth is concerned. 
They began to make an appreciable growth at 1,5, the lowest temperature 
tried, after 10 days. Artocarpi, a low-temperature form as indicated by 
its optimum, made some growth at 9° but none at 7°, while chinensis, 
which has a high optimum, made some growth at 10.4° but none at 7.5°; 
in other words, growth was inhibited at practically as high a temperature 
in the low-as in the high-temperature form. At 11° and 9.8® oryzae and 
delemar, two forms very closely related both morphologically and physio¬ 
logically, made some growth in 4 and 16 days, respectively. However, 
at 7.5® growth was entirely inhibited. Oryzae was not subjected to any 
temperature between and 7.5°, so it is possible that some growth 
might have taken place at a teffip^ature somewhat below 11°. Han- 
zawa found that this species made some growth at 6®, while the upper 
and lower limits for delerttarMere found to be 12® and 42°, respectively. 
It may be said, then, that the minimuin temperature for growth varies 
with the time for the fimt 5.. to 15 days; depending upon the species. 
After that time the try^ minimum—that is, the lowest temperature at 
which growth will ta^ place regmdless of ^e time—^is reached. Thus 
growth decreases as the temperature is lowered until a point is reached 
where it is entimiy inhibited. However, cultures which failed to grow 
after 30 days, at the inhibitive temperature or lower develop rapidly when 
transferred kp a more favorable temperature, showing that the proto¬ 
plasm of the spore has suffered no harmful effects. These results are in 
general accord with those of other workers with other organisms. 
It was pointed out above that there was visible growth at the 
maximum tem^rature by .the end of the first 24 hours in each species. 
It would appear from the graphs that the maximum temperature in all 
cases is fixed—tfeat is, that it does not change during the course of the 
experiments as' does the minimum. However, this is not the case. 
Delemar, for example, made a growth about 9 mm. in diameter at 41° C. 
in the first 24 hours, which reached 10.5 mm. during the following 
24-hour period and then ceased altogether, the mycelium failing to grow 
when placed at a favorable temperature. In this case the maximum 
for the first 48 hours was about 41®, after which even at 38° the growth 
was considerably retarded although not inhibited within the time limit 
of this experiment. Shifting of the maximum was noted with the other 
species. No doubt if temperatures sufficiently close were tried over a 
considerable length of time and by a method sufficiently delicate to 
determine accurately yery small increments of growth a so-called shifting 
of the maximum be found in all cases. As the temperature rises 
above the optimt^'«Ore^rding ^odh followed by an inhibiting effect 
is noted. A comparatively short exposure to the inhibiting temperatures 
results in the death of the organism, although it is possible that a tem¬ 
perature slightly below the maximum established might be found which 
would iidiibit growth for a considerable length of time and yet would 
not kill the Jungus. Fawcett (6) has found a similar shifting of the 
maximum. Shifts from 36® to 31^, 38° to 35®, 46® to 35^ were noted in 
Pythiacystis citrophthora Smith and Smith, Phytophthora ierrestria Sher- 
bakoff, and Diplodia naialensis Evans, respectively. All of these fungi 
