18 BULLETIN 907, IT. 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 90° 

 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. 



