EFFECTS OF CERTAIN INSECTICIDES AND INERT MATERIALS UPON THE TRANSPIRATION RATE OF BEAN PLANTS

The changes in physiological processes of plants brought about by the application of spray materials are not well understood, nor have they been investigated in detail. That such changes do occur is evidenced by both the beneficial and the harmful effects of these compounds quite apart from their value as fungicides or insecticides. The increased growth and greater yield of potatoes sprayed with Bordeaux, the shot-hole effect of copper fungicides on peach leaves, the russeting of fruit and burning of foliage by arsenicals all point to profound changes in the physiology of the sprayed tissues. In an attempt to determine the basis for the relative "safeness" of certain arsenates as compared with others, investigations into the effects of both kinds of sprays on the physiological processes in plants have been made. The process most widely studied in this connection has been transpirationi. Some writers have suggested that the phytocidal action of certain sprays might be attributed, at least in part, to the sudden increase in the rate of water loss from the sprayed plants. Thus it was thought that perhaps a so-called "safe" compound which did not cause the typical burning of sprayed leaves, was innocuous because it did not bring about the inierease in water loss which resulted when the injurious sprays were applied to the leaves. Not all investigators are agreed as to the effect of sprays on transpiration. Many have recorded results in which there was no increase, but a decrease, or no change at all in the rate of water loss. In fact, it has been suggested that the stimulatory effect of Bordeaux on potatoes may be attributed to a conservation of the water supply. The earlier workers investigated the effect of Bordeaux oni crop planits. In general, their results showed a decrease in the transpiration rate of the sprayed plants as compared with that of the controls. Many of the data, however, were not very quantitative. Some time later, DUGGAR and COOLEY (3), in studies of cut planits in potometers, found that Bordeaux increased the transpiration rate of castor bean, squash, Phytolacca, potato, and Iresine. They also studied the rates