FUMIGATION OF CITRUS PLANTS. 9 
ferent conditions. In each of the five conditions the prefumigation 
sun-exposed plants developed decidedly greater injury than those 
that were in shade before treatment. ‘The results of experiment 
18, in which plants were exposed to a hot sunshine (83° F.) imme- 
diately before fumigation and fumigated at a high temperature, 
show all sun-exposed plants killed regardless of the postfumigation 
conditions; yet others in the shade at approximately the same pre- 
fumigation temperature (76° F.) and placed at a temperature of 
56° F. after the treatment had only the very tenderest foliage singed. 
The effect of prefumigation sunshine is not so conclusively brought 
out in the other experiments, but, with the exception of No. 3, it 
appears to have intensified the injury in at least a few of the trees 
treated. Experiment 3 alone shows no difference between plants 
in the shade and those in the sunshine previous to fumigation. It is 
noted in this case that the sunshine temperature was 60° I. and the 
fumigation and postfumigation conditions were equally cool, all 
three being ideal for exposure to cyanid gas. 
A comparative study of the temperature before and after treatment 
shows that the effect of prefumigation sunshine is modified by the 
degree of heat present at these different times. For instance, in 
experiment 3 where the sunshine appeared not to affect the degree 
‘of injury more than the shade, all fumigation conditions, the pre- 
fumigation, postfumigation, and actual fumigation, approximated 
60° F. On the other hand; experiment 2, which was performed 
with the same type of plants, the same dosage, and at approximately 
the same temperature, exhibited a decided difference in injury between 
the prefumigation shade and sunshine-exposed plants, the injury 
in the latter being greater than for experiment 3. It is noted that 
the sun temperature in experiment 2 was 75° F., whereas in experi- 
ment 3 it was 60° F., which shows that the degree of injury attribut- 
able to sunshine increased with the increased temperature. Thus a 
hot sunshine before fumigation is more to be avoided than a cool 
sunshine. 
In conclusion it can be stated that the experimental evidence in 
this paper appears to show that sunshine coming in contact with 
citrus plants before fumigation tends to produce greater injury than 
where plants are in the shade or darkness; that sunshine accom- 
panied by a high temperature is more injurious than if accompanied 
by a low temperature; that the degree of injury is modified by the 
postfumigation conditions, greater injury developing at high tem- 
peratures than at low temperatures; that the most critical environ- 
ment is to subject plants exposed to a hot sunshine before fumiga- 
tion to a hot sunshine after fumigation; finally, that a high tempera- 
ture during fumigation probably increases the injury of prefumiga- 
tion sunshine-exposed plants over that taking place at a low tem- 
perature. 
4533°—Bull. 907—20——2 
