A. R. SCHRANK 



131 



when the curvature starts toward the stimulated side. (A good guess 

 would be that curvature due to growth starts as the coleoptile tip passes 

 its prestimulation position.) Thus it is impossible to state in this situation 

 whether or not the electrical polarity is established before the curvature 

 starts. Logically it would seem that it is, because the rate and magnitude 

 of the curvature can be approximately predicted from the magnitude of 

 the electrical response and its rate of change. 



MILLIVOLTS 



-10 

 -20 

 -30 



' I 

 1 / 



ns.- / 



■^ 



DURATION OF STIMULUS 



€ 4 seconds 

 • 6 seconds 

 o 8 seconds 



J L_J L_J L— L 



CURVATURE 



20 MINUTES 



Figure 4. A. Transverse electrical polarities established by Avena coleoptiles 

 1.67 millimeters below the apex in response to mechanical stimulation of one 

 side of the apical 10 millimeters. Each curve is an average of 10 experiments. 

 B. Corresponding average curvatures in scale divisions of 18 per millimeter. 



