18 BULLETIN 907, U. S. DEPARTMENT OF AGRICULTURE. 
temperature for these five experiments is 80° F., a maximum only a 
few degrees higher than the limit of optimum temperatures estab- 
lished for field fumigation. On the other hand, in the set of experi- 
ments (1, 12, 14, 15, and 18) which shows a difference in injury 
between plants submitted to high and those submitted to low post- 
fumigation temperatures, the range is from a minimum of 23° in 
experiment 18 to a maximum of 34° in experiment 14. In short, the. 
minimum range in the last set of experiments is 7° higher than the 
maximum range in the first set which developed no difference of 
injury; furthermore, the maximum postfumigation temperatures are 
higher, ranging from 86° to 90° F., except in experiments 14 and 18, in 
which they are 80° and 79° F. respectively. Another consideration 
of special importance is the temperature of fumigation, which in the 
first set of experiments ranged from 60° to 69° F., whereas in three 
of the five experiments of the set which developed differences in 
injury the fumigation temperature ranged from 85° to 92° F. Two 
of the experiments in this last set, namely, 1 and 12, were performed . 
at temperatures of 60° and 64° F. In these two experiments, how- 
ever, the postfumigation temperatures were very high, 86° and 99° 
F., and the range between the cold and hot postfumigation tempera- 
tures was from 26° to 30°. | 
The general conclusion to be drawn from these experiments is that 
the postfumigation temperature exerts an influence on the degree of 
injury, especially at temperatures of 80° F. or above. The effect of 
such high temperatures is modified by the temperature of fumigation; 
for instance, a high postfumigation temperature preceded by a high 
fumigation temperature is more destructive to plant tissue than a 
high postfumigation temperature preceded by a low fumigation tem- 
perature. In fact, as is well shown in experiments 10 and 15, it is 
possible to subject plants treated at such low temperatures as 60° to 
65° F. to moderately high postfumigation temperatures (79° and 80° 
F.) without any more injury than at the lower temperatures of 64° or 
65° F. The postfumigation temperature of shade or darkness is so” 
closely related to the actual fumigation temperature in modifying 
plant injury that it is important to take cognizance of each in plant 
treatment. The influence of temperature on plants subjected to 
sunshine following treatment has been discussed under the heading 
‘Sunshine.’ To avoid injury, or at least to reduce the possibility 
of damage to the lowest degree, the data presented in this paper 
appear to indicate that after fumigation plants should be placed at 
temperatures below 80° F. The exact number of degrees the opti- 
mum falls below 80° will depend on the prefumigation and fumigation 
temperatures. When these are ideal the maximum optimum ap- 
parently approximates 80° F., but if they are not the optimum is low- 
ered a few degrees. 
