FUMIGATION OF CITRUS PLANTS. Sen! 
under shade temperatures of 79° and 90° F. immediately after the 
exposure, although plants exposed to the sunshine (76° F.) at the 
same time had almost all foliage, both tender and resistant, destroyed. 
Plants held in the shade for 30 minutes and one hour, respectively, 
after treatment and then subjected to sunshine at temperatures of 79° 
and 80° F. were about equally affected and this amounted to having 
a large part of the old resistant foliage destroyed. The injury, how- 
ever, was noticeably less than where the plants had been exposed 
immediately after the treatment. Plants withheld for a period of 
two hours before placement in the direct sunshine had the tender 
erowth destroyed and a few old leaves slightly affected, while plants 
held three hours before placement in the sunshine were no more 
HOURS 
Fic. 1.—Graph showing relation of plant injury toesposute to sunshine at different periods after fumiga- 
10n, 
injured than those placed in the shade, only the tenderest growth 
being burned in either case. 
The results of this experiment are fully corroborated by both 
experiments 22 and 23, and in part by experiment 21. In number 
21, however, although the results agree with those in the other three 
experiments in showing that sunshine increases the toxic action of 
hydrocyanic-acid gas to the plant for a period of fully one hour after 
exposure, it differs somewhat in that the full effect of the sun is shown 
for one hour after which its influence quickly disappears. 
The evidence presented in these four experiments shows that 
sunshine affects the degree of injury to fumigated citrus trees usuaily 
for a period of at least two hours after treatment where dosages 
equivalent to those used in these experiments are given to growing 
plants; that the greatest injury follows-exposure to sunshine imme- 
