806 
Journal of Agricultural Research 
Vol. XXX, No. 9 
and 29.8° was so marked as to indicate 
that the latter temperature is near the 
upper limit. 
Rhizopus artocarpi caused slight, if any, 
infection at 32° C., considerable at 28.1°, 
but none at 33° (Table III and fig. 8); 
32° therefore is apparently near the 
upper limit. It is possible that in case 
of the last three species the maximum 
might be raised some if a longer time 
were employed; but this seems im¬ 
probable, however, for at these high 
temperatures if infection does not occur 
during the first two days the potatoes 
remain uninfected. Table VI contains 
a summary of cardinal temperatures 
Table VI.— Summary of the cardinal temperatures of the six species of Rhizopus 
studied 
Species 
Minimum 
Optimum 
Maximum 
Absent Present 
! 
Absent Present 
R. tritici____ 
0 c. ° c. 
3. 4 
°C. 
32 to 34. 5 
33 
32 to 34 
18. 5 to 23 
22 to 23 
18. 5 to 23 
23 to 24 
0 C. °C. 
44 42 
44 42 
44 42 
28.8 24.5 
34.0 30.0 
34.5 29.8 
33.0 ! 32.0 
1 
R. oryzae__ _ . __ 
5 9.0 
5 
R. maydis.. _____ . _ . 
R. nigricans (strain a)__ _ ... . 
_s 3.4 
R. nigricans (strain b )_ _ . 
5.0 i 7.0 
_ 3.4 
R. reflexus_ . _ __ _ 
R. artocarpi_ .... 
5 | 12.0 
1 
Table VII.— Lower temperature limits for infection of sweet potatoes hy Rhizopus 
tritici, R. oryzae, R. maydis , R. nigricans (strain a), R. reflexus and R. artocarpi 
Organisms isolated 
Organism with 
which potatoes 
were inoculated 
Time 
in days 
after 
inocu¬ 
lation 
Tem¬ 
pera¬ 
ture 
Num¬ 
ber of 
pota- 
j toes 
inocu¬ 
lated 
Num¬ 
ber of 
pota¬ 
toes de¬ 
cayed 
Num¬ 
ber of 
isola¬ 
tions 
made 
Num¬ 
ber of 
times 
organ¬ 
ism 
used in 
inocu¬ 
lation 
was 
isolated 
Other organisms isolated 
Rhizopus tritici... 
25 
0 c. 
5.0 
20 
20 
19 
19 
Do_ 
51 
5.0 
21 
21 
21 
19 
1 Botrytis, 1 Mucor. 
Do_ 
52 
3.4 
18 
18 
14 
5 
Botrytis and R. tritici mixed, 6; 
R. nigricans 
25 
5.0 
22 
10 
9 
6 
Botrytis, 1; bacterium, 2. 
1 Rhizopus sp. and bacterium; 
(strain a). 
Do_ 
51 
5.0 
20 
20 
20 
20 
2 Mucor. 
Do.. 
52 
3.4 
18 
18 
9 
3 
6 Botrytis and Mucor mixed. 
R. reflexus.. 
25 
5.0 
21 
21 
16 
12 
4 Rhizopus sp. and bacteria. Rhi¬ 
Do.. 
51 
5.0 
18 
18 
0 
0 
zopus here probably reflexus. 
Decay too far advanced for isola¬ 
Do_ 
52 
3.4 
18 
18 
18 
18 
tion. 
R. artocarpi_ 
25 
5.0 
20 
(°) 
0 
0 
Do__ 
51 
5.0 
20 
20 
15 
0 
1 Mucor; 1 unknown organism; 
R. maydis_ 
51 
5.0 
14 
14 
12 
0 
10 Botrytis; 2 Penicillium; 1 
bacterium. 
7 Botrytis; 1 R. nigricans; 2 Mucor; 
Do_ 
52 
3.4 
18 
18 
12 
0 
2 Mucor and Botrytis. 
8 Botrytis; 1 bacterium; 3 Mucor. 
R. oryzae_ 
51 
5.0 
18 
17 
15 
0 
9 Botrytis; 1 Mucor; 3 Pencillium. 
Control.. 
Do.. 
Do_ 
25 
51 
52 
5.0 
5.0 
3.4 
21 
18 
18 
0 
18 
13 
0 
13 
13 
2 unaccounted for. 
4 R. nigricans; 6 Botrytis; 3 Peni¬ 
cillium. 
2 R. nigricans; 7 Botrytis; 2 Mucor. 
Decay just started but dried up. 
