Jan. 22, 1917 
Temperature Relations of Apple-Rot Fungi 
161 
DISCUSSION OF RESULTS 
A comparison of the different tables and figures shows that the tem¬ 
perature response of a particular organism is modified by the medium 
upon which it is grown. The contrasts have been particularly striking 
between the behavior of the fungi on the living fruit and on dead organic 
matter. On corn-meal agar most of the fungi have grown from the first* 
day even at rather low temperatures, while on apples there has usually 
been an initial incubation period of very slow growth which gradually 
passed over into a later one in which decay proceeded rapidly. In the 
initial stages of growth on the fruit the fungus must live almost entirely 
as a parasite and has not had time to build up reserve food material or 
secrete enzymes in quantity, while in the later stages it has a continually 
increasing mass of mycelium and the possibility of obtaining much of 
its food saprophytically from the tissue already broken down. The 
initial incubation stages of decay have been much more inhibited by 
low temperatures than the later stages, leading in some cases to a delayed 
development of rot and in others to a total prevention of it at a tem¬ 
perature at which the fungus was capable of making a rapid saprophytic 
growth. The inhibition at low temperatures was more pronounced with 
immature fruit than with mature specimens and with weak parasites than 
with strong ones. 
Glomerella cingulata was unable to make any growth at 5 0 or io° and 
Fusarium radicicola at 15 0 on Yellow Newtown or Winesap apples, but 
both fungi grew well on corn-meal agar at all three of these temperatures. 
Neofabraea malicorticis and PenicUlium expansum had produced no evi¬ 
dent rot on Winesap apples at o°, 5 0 , or io° at the end of two weeks, but 
they finally caused fruit decay at all these temperatures. Both g'rew from 
the first day at 5 0 and io° when inoculated into corn-meal agar, and both 
had made a measurable growth on this medium at o° by the end of the 
second day. Similar contrasts were found with several of the other fungi, 
but were not evident with Sclerotinia cinerea and Sphaeropsis malorum , 
two of the more distinctly parasitic fungi tested. The former was com¬ 
paratively little delayed at low temperatures on either fruit or corn-meal 
agar; the latter was greatly delayed at o°, 5 0 , and io° on both food 
materials. 
The early stages of the rots were not only partially inhibited by low 
temperatures but sometimes entirely prevented at temperatures at which 
the later stages could develop. In the commercial cold-storage experi-j 
ments it was found that PenicUlium expansum was able to make a good 1 
growth at o° on fruit on which it was entirely unable to make a start at 
that temperature. This could not have been a question of germination, 
as the fruit was in the center of the barrel, and there would have been 
ample time for this to have taken place before the cooling was completed. 
This fact is very significant in showing the value of immediate as com- 
