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 smishine 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 

 smishine 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 hr 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. 



