FUMIGATION OF CITRUS PLANTS. 17 



in experiments 14, 15, and 18, which were fumigated at temperatures 

 ranging from 86° to 92° F. This would appear to indicate that the 

 temperature of fumigation within the limits of those experiments, 60° 

 and 92° F.,. has little if any modifyhig influence on the resulting 

 degree of injury to plants subjected to the sunshine after treatment. 

 It happens, however, that the prefumigation or postfumigation 

 conditions in experiments 14, 15, and 18 were exactly comparable to 

 those in none of the other experiments mentioned. Although section 

 1 of experiment 15 approximates experiment 10 as to prefumigation 

 and postfumigation conditions, it is seen that the maximum sun tem- 

 perature for the day in experiment 15 was 77° F., whereas in experi- 

 ment 10 it was 102° F. Therefore, definite conclusions regarding the 

 influence of the temperature of fumigation on plants subsequently 

 placed in sunshine can not be drawn until there is further experi- 

 mental evidence bearing on this subject. 



The effect of postfumigation sunshine on plant injury appears to be 

 modified to a certain degree by the prefumigation light condition. 

 This is well shown by experiments 2 and 14, in which the damage to 

 the plants under postfumigation sunshine is greater in the case of 

 plants exposed to prefumigation sunshine than to plants in prefumi- 

 gation shade at a comparable temperature. It is probable that the 

 prefumigation temperature modifies to some degree the effect of 

 postfumigation sunshine, but this point is not conclusively proved 

 in this paper. 



TEMPERATURE. 



The importance of the temperature to which plants are subjected 

 after fumigation as a factor bearing on plant injury is brought out by 

 the experimental data presented in experiments 1, and 10 to 19. It 

 is shown in experiment 12 that fumigated plants placed immediate 1 y 

 after treatment under a shade temperature of 88° F. or a darkness tem- 

 perature of 90° F. are slightly more injured than those placed at a 

 temperature of 60° F. A like condition is presented in experiment 

 15 between postfumigation temperatures of 63° F. and 89° or 91° F. 

 Experiments 1, 14, and 18 also show slightly increased injury due to 

 higher postfumigation temperatures in the shade or darkness. On 

 the other hand, each experiment of numbers 2, 10, 13, 16, .and 17 

 shows the same degree of injury for plants subjected to different 

 temperatures- of shade and darkness following fumigation. An 

 examination of the details of these experiments, however, brings out 

 a significant difference between the two groups. In the set of experi- 

 ments (2, 10, 13, 16, and 17) in which there was no apparent difference 

 in injury due to the different postfumigation temperatures it is seen 

 that the difference between the high and low temperatures in any one 

 experiment varies from 9° in experiment 16 to a maximum of 16° in 

 experiment 17; furthermore, that the maximum postfumigation 

 4533°— Bull. 907—20 3 



