CHAPTER III 

 PHYSIOLOGICAL EFFECTS ON PLANTS 



s 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. In 1 894 

 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 Jose 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 



12 



