CHAPTER III 
PHYSIOLOGICAL EFFECTS ON PLANTS 
Al NOTED in a previous chapter, early experi- 
menters had observed the burning effects of 
the gas upon foliage when used under certain 
conditions and overcome the difficulty by 
night fumigation. It remained for Dr. Albert F. Woods, 
now Chief of the Division of Vegetable Physiology and 
Pathology, United States Department of Agriculture, 
and an assistant, P. H. Dorsett, to solve this problem 
in connection with certain greenhouse plants. In1894 
they began a series of experiments, and proved con- 
clusively that plants are less injured by a short ex- 
posure to a relatively large amount of gas than by a 
long exposure to a relatively small amount, and also 
that a stronger dose a short time was more destructive 
to the insects affecting the plant. They further de- 
monstrated the physiological effect of the gas upon 
the plants by subsequent experiments. They summed 
up the resisting power of the plant as dependent largely 
upon the open and closed condition of the breathing 
pores of the leaf, the peculiarities of the cell contents, 
and the temperature of the inclosure. 
I found the same variations in the field, where we 
used the gas largely in the control of San José scale 
and other insects. ‘The first problem taken up in this 
connection was the physiological effect of the gas 
upon deciduous trees in the East. The conditions in 
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