4 Journal of Agricultural Research voi. xxiv. No. i 
number of microns in length might have been employed; but the measure 
selected was easier to determine, since the spore was always present 
with the germ tube for quick comparison, while considerable time would 
have been required to bring the spore in line with the micrometer scale 
for measurement. In these studies time was a very important factor, 
since germination often occurred in three or four incubators at nearly 
the same time, often not over from 5 to 15 minutes apart. Some care 
had to be exercised, especially at the less favorable temperatures, as 
often one or a very few spores would start to germinate considerably in 
advance of the remainder. However, by examining the hanging drop 
cultures frequently it was possible to determine with a fair degree of 
accuracy the point sought. Slides were examined near the incubators 
and were kept out usually less than a minute. Only at the higher tem¬ 
peratures was there any appreciable fluctuation as a result of opening 
the doors, and in such cases the normal temperature was quickly restored. 
The results obtained from the study of the germination of the spores 
of 10 of the species is shown by the curves in figure i. The germination 
of Rhizopus maydis spores was not studied for the reason that under 
the conditions imder which the cultures were grown spores were not 
produced in sufficient quantity to carry out the experiment. 
In the curves in figure i the time in hours necessary for the germ 
tubes to reach the length of the diameter of the spores was plotted on 
the abscissa, while the temperature in degrees centigrade was plotted 
on the ordinate. The maximum temperature for germination as indi¬ 
cated by the table is that temperature at which no germination took 
place. The temperature at which germination will just take place is 
very difficult to determine, since at or 2® C. below the maximum it 
frequently starts and then stops before the germ tube reaches the diameter 
of the spore. For example, Rhizopus artocarpi spores germinated readily 
at 32.3® while at 33.4° offiy about one-half of i per cent of the spores sent 
out germ tubes, which finally reached a length equal to twice the diameter 
of the spore and then stopped. At 34.5° the spores became somewhat 
swollen, which is a condition always preceding the extrusion of the germ 
tube. After 48 hours the spores had been killed at the two higher tem¬ 
peratures, as indicated by the fact that they failed to germinate when 
placed at a temperature favorable for germination. Similar results were 
obtained with other species. No attempt was therefore made to estab¬ 
lish a definite maximum, but it may be said that in general it is some¬ 
where from I® to 2*^ lower than the temperature plotted as being the in¬ 
hibiting temperature. In every case where there was no germination 
within 24 to 48 hours the spores were found to have been killed. The 
temperatures just above the maximum which inhibited germination of 
the spores of the different species are as follows: artocarpi^ 34*5°; tritici, 
delemar, oryzae, nodosus, and arrhizus, 45.5°; chinensis, 52°; reflexus, 38®; 
nigricans and miarosporus, 34®. The lower temperature limits for germi¬ 
nation for only two of the species, nigricans and microsporus, are shown 
by the curves, since in all other cases the time for germination at the 
minimum temperature was more than 100 hours. The spores of chinensis , 
oryzae, and delemar had not germinated during 30 days* exposure at 8.5*^, 
7®, and 7®; but germination did take place in that length of time at 
temperatures of 10®, 9®, and 8.7®, respectively. On ^e other hand, 
the spores of the remaining species, reflexus^ arrhizusy triticiy nodosusy and 
artocarpiy germinated at 1.5®, the lowest temperature tried, in 5, 15, 22, 
14, and 6 days, respectively. The percentage of spore germination at 
