22 . BULLETIN 907, U. S. DEPARTMENT OF AGRICULTURE. 
diately or within a few minutes after the fumigation; that the influ- 
ence of sunshine which first reaches plants 30 minutes after treatment 
is practically the same as that of sunshine which first reaches the 
plants one hour after fumigation, and in all cases is severe; that the 
effect when plants are withheld for three hours before exposure to 
sunshine is seldom greater than where they are kept in the shade or 
in darkness at equal temperatures; in short, that sunshine appears 
to affect fumigated plants little or not at all at periods exceeding 
three hours after treatment. : 
THE EFFECT ON PLANT INJURY OF TEMPERATURE, LIGHT, AND 
MOISTURE DURING FUMIGATION. 
The effect of certain weather conditions during the period when 
plants are actually exposed to hydrocyanic acid is brought out 
clearly in experiments 1 to 27. 
DARKNESS AND SHADE. 
The comparative influence on plant injury of shade to darkness 
during fumigation is shown by certain experiments, of which num- 
bers 10 and 16 are especially representative. In these experiments 
are found practically identical prefumigation and . postfumigation 
conditions, and the actual fumigation environments differ only in 
that No. 10 was performed in the dark while No. 16 was carried on 
in diffused light. The results of these experiments indicate no dif- 
ference in degree of injury between plants fumigated in the shade and 
those fumigated in darkness. Experiments 5 and 17 contain a series 
of plants which present results corroborating those shown in experi- 
ments 10 and 16. A careful comparison of other experiments given 
in this paper supports the conclusion that citrus plants are as safely 
fumigated in diffused light as in total darkness. | 
SUNSHINE. 
No experiments were performed in which plants were exposed to 
sunshine during treatment, but in consideration of the results pre- 
viously shown where plants exposed to the sunshine immediately 
after fumigation developed very much more severe injury than 
others in the shade or dark at equal temperatures, it would appear 
that at least equally severe injury would develop from sunshine dur- 
ing the actual treatment. Factors which bring about injury from 
exposure to sunshine after fumigation would appear to be present 
in at least equal force in exposure to sunshine during actual 
treatment. Sunshine exposure during actual treatment would be 
possible only under glass, and in such cases would be accompanied 
by a temperature greater than that of the outside air. 
