A. R. SCHRANK 133 



Effects of Applied Current on 

 Electrical Pattern and Curvature 



Perhaps the most direct way to alter the electrical field of a living 

 organism is to superimpose a field or polarity of external origin. This 

 approach has been taken by several investigators. Wilks (39), Clark 

 (12,13), duBuy and Olson (14), Cholodny and Sankewitsch (10), and 

 Kogl (15) have all studied the various aspects of applied direct current 

 on growth and auxin transport in the Avena coleoptile. Some of their 

 reports (10,15,39) indicate that the effects of applied current on growth 

 responses are dependent on the polarity of the current, but one main- 

 tains that the curvature obtained is not dependent on the polarity of 

 stimulation (14). Since the publication of these observations an additional 

 series of papers has appeared in which the effects of applied current on 

 the electrical polarity and curvature of the coleoptile were observed 

 simultaneously. In the experiments to be examined at present the current 

 was applied either transversely or longitudinally. 



Current applied transversely. — When 5 to 20 microamperes of direct 

 current are applied transversely for 2 to 10 minutes the coleoptile always 

 responds by establishing a transverse electrical polarity (28). (Control 

 experiments show that such electrical responses are obtained only from 

 living tissue.) In Figure 5 a group of average curves are shown, which 

 represent the transverse electrical polarities induced by applying a given 

 current (10 microamperes for 10 minutes) at various distances below 

 the apex. These curves show that a given quantity of current induces 

 the maximum electrical polarity when it is appHed to levels more than 

 5 millimeters below the apex. The fact that these electrical polarities 

 are established is taken to indicate that the applied current did flow 

 through the Hving tissue, a point not always clear in previous papers. 

 Also current applied transversely in the manner just described always 

 causes the coleoptile to bend. Figure 6 presents a diagrammatic account 

 of this bending process when 10 microamperes were applied for 10 

 minutes at a level 10 millimeters basal to the apex. The initial curvature, 

 in and above the contact region, is toward the positive pole of the 

 current-applying circuit; however, there is a subsequent bending, basal 

 to the contact region, in the opposite direction. The maximum angular 

 curvatures that were observed in the initial direction, resulting from 

 current (10 microamperes for 10 minutes) applied transversely to various 

 levels below the apex, are shown in Table i. 



