FUMIGATION OF CITRUS PLANTS. a 
tain experiments already presented in this paper have shown that 
plants in a prefumigation and fumigation environment of darkness (in- 
dicating closed stomata) were severely injured by placement in sun- 
shine immediately after the exposure, while check plants placed in 
the shade at an equal temperature were little affected. In these cases 
the increased damage to the sun-exposed plant was brought about in 
spite of the fact that the stomata were apparently closed during the 
fumigation. Furthermore, data have been collected during daylight 
work, both in the morning and afternoon, showing that trees some- 
what protected from the direct sun were little affected by a strength 
of gas that severely injured trees in the direct sunshine treated at the 
same time. On the other hand, the increased injury to plants in a 
prefumigation condition of sunshine, as previously explained, and 
observation that greater injury is usually apparent during morning 
orchard fumigation than during that performed late in the afternoon 
at an equal temperature, might indicate possible stomatal influence 
when viewed in the light of Lloyd’s (9) conelusions that the morning 
sun may hasten stomatal opening, that this opening is at its maximum 
toward midday, and that closure occurs during the afternoon. 
Stone, Moore, and others conclude that a strong concentration of 
gas tends to close the stomata. This closure of the stomata from 
fumigation would reduce the rapidity of the escape of gas which 
remained in the intercellular spaces after treatment and might 
thereby modify the degree of injury, especially in plants subjected to 
_ such adverse conditions as postfumigation sunshine. 
The condition of the soil apparently influences cyanid injury from 
sunshine, as shown in the case of a 10-acre citrus orchard fumigated 
during a clear hot day in November, 1919. This orchard was so 
. irrigated that the soil nearest the head of the furrows was thoroughly 
wet to a normal depth, whereas the soil at the lower end of the furrows 
was for the most part wet only for a few inches at the surface, or 
sometimes not atall. The trees reflected this lack of required moisture 
in their general less healthy appearance. The tents were strung in 
the direction of the irrigation furrows. Severe injury resulted from 
the fumigation, amounting almost to complete defoliation on the 
sunward side of a large part of the trees. This injury was confined 
almost exclusively to the trees on the dry soil, those on the moist 
soil being very little affected. The explanation is that the trees which 
had long suffered from lack of moisture were in a weakened condition 
at the time of fumigation, whereas the others were not. 
TEMPERATURE. 
It has been clearly shown by the experimental evidence presented 
in this paper that temperature exerts one of the most important 
modifying influences on injury from fumigation. Furthermore, not 
