6 
Journal of Agricultural Research 
Vol. XXIV, No. I 
this temperature was often small, and only in the case of reflexus did any 
appreciable growth take place within the time limit of these experiments 
(30 days). 
The optimum temperatures as obtained by this method are as follows: 
artocarpi, 26° to 29° C.; nigricans and microsporus^ 26° to 28®; iritici, 
delemary nodosuSy oryzae^ and arrhizus, 36° to 38°; reflexus 30° to 32®; 
chinensisy 43® to 45° C. Any attempt to determine a closer optimum 
seemed impracticable, since the rate of germination at these temperatures 
is so nearly the same. For the convenience of the reader and for the 
greater ease of comparing the effect of temperature on germination, 
growth, and fruiting these data are set forth in Table I and will be 
referred to later. 
The curves (fig. i) show that the species studied fall into three groups 
according to their response to temperature. Chinensis stQ.tids out con¬ 
spicuously as a species with a high optimum, although there is a con¬ 
siderable range through which good growth will take place. In fact, 
this species has a wider temperature range, about 30° C., through which 
the spores germinate readily, than any of the others studied, which 
indicates that it is less sensitive to heat. Artocarpi probably stands at 
the other extreme, although its spores germinate well within a range 
of 20® (10° to 30^). The drop on both sides of the curve is very abrupt. 
Owing to its sensitivity to heat considerable difficulty was at first ex¬ 
perienced in keeping this fungus alive. This species was the most 
erratic in its behavior, requiring more study to determine its temperature 
relations than any of the other species. 
Along mth artocarpi as species with comparatively low optimums and 
maximums may be placed reflexuSy nigricanSy and microsporus. The 
results seem to indicate that the two latter species have the lowest mini¬ 
mum, since their spores germinated much more quickly at the lowest 
temperature tried. 
The remaining five species are very similar in regard to their maximum 
and optimum temperatures, differing only in the time necessary for germi¬ 
nation, which varies at the optimum from 3 hours (oryzae) to 5^ hours 
(arrhizus). As pointed out above, however, these species also differ in 
their lower temperature limits in that the spores of oryzae and delemar 
failed to germinate at 7° C. while those of the other three germinated 
at 1.5°. 
The temperature relations of several species of Rhizopus have been 
studied by Hanzawa (p) and Lendner (rj, p. 111-127), The former sepa¬ 
rated nigricans from the other species studied by him by the fact that it 
was the only one which did not grow at 37° C., and the latter separated 
it from oryzae because it did not grow on potato at 39°. Hanzawa states 
that nigricans would not grow at blood temperature (35® to 37°). He 
also found that chinensis spores did not germinate at 6° and that those of 
delemar would not germinate below 12° or above 42*^. Hagem {8)y work¬ 
ing with Mucor (Rhizopus) nodosjis (Namyslowski), found that its 
spores did not germinate at 43° to 44° C. Ames (i) found that the 
spores of R. nigricans failed to germinate at 1° or at 42® but germinated 
at 3® to 4° and 41°, the optimum being from 38° to 41where germina¬ 
tion took place in 5^^ hours. Stevens and Wilcox (20) found Siat this 
fungus could mature a few sporangia on ripe strawberries at 36° to 37°. 
The difference in temperatme limits given by different investigators 
for this fungus is difficult to understand. This disagreement in results 
might be due to several causes, such as the use of different strains, to 
