138 PLANT GROWTH SUBSTANCES 



is distinctly different. These facts definitely show that the polarity of the 

 applied current has an effect on the electrical response. 



In Figure 7B the corresponding curvatures are represented by graphs 

 of the movement of the apex and by numerals indicating the angular 

 curvature at the end of the experiments. The direction of bending is 

 always toward the side on which the contacts were placed, thus confirm- 

 ing, in this part, the observations of duBuy and Olson (14). However, 

 curves I and II in Figure 7B demonstrate that a given current flowing 

 from the base toward the apex through the coleoptile induces curvature 

 more effectively than the same current flowing in the opposite direction. 

 On the basis of known effects of current on elongation (10,39) '^his can 

 be interpreted to indicate that current flowing toward the apex inhibits 

 elongation more effectively than the same current flowing in the reversed 

 direction. These observations, in contradiction to the results previously 

 published by duBuy and Olson (14), show that the magnitude and the 

 temporal sequence of the curvature are dependent on the polarity of 

 the applied current. This point very hkely will assume considerable 

 importance in the final and complete explanation of how current affects 

 growth. 



Finally, one additional group of experiments will be introduced. 

 It has recently been shown that direct current, (10 microamperes for 

 2 minutes) apphed in the manner just described, always inhibits bending 

 toward 200 meter-candle-seconds of unilateral illumination (31). The 

 extent of the curvature inhibition and the temporal sequence of events 

 are again dependent on the polarity of the apphed current and on the 

 position of the contacts with respect to the light source. Results of these 

 experiments show that current applied longitudinally on the hghted 

 side inhibits rather than accelerates curvature toward the light, while 

 current applied to the shaded side inhibits bending toward the light 

 somewhat more effectively. The polarity of the applied current which is 

 most effective on the lighted side is least effective on the shaded side. 



The results of these last experiments seem to indicate that longi- 

 tudinally applied current brings about the growth curvature by in- 

 fluencing the auxin-controlled mechanism, but it is rather difficult to 

 explain, on the basis of the available evidence, precisely how applied 

 current affects growth. It has been observed that current applied in this 

 manner reversibly inhibits protoplasmic streaming (14). If the transport 

 of auxin is dependent on the streaming, it follows that current could have 



