126 PLANT GROWTH SUBSTANCES 



that the Inside Is electropositive to the outside. In the more basal regions 

 the radial polarity is reversed. This would Indicate that for the Internal 

 longitudinal polarity the basal region Is electronegative to the apex 

 (27,39). ^^^ ^1^ of the data in the literature are in agreement on this 

 point (12). Finally, Figure i shows that no transverse polarity (circuits 

 A, B, C, D, and E) Is manifested by the nonstimulated coleoptile when 

 it Is kept In the vertical position. 



The possibUity of a definite system of electrical currents within the 

 coleoptile becomes apparent from the figure. The implication is that the 

 electromotive forces of the cells would supply the energy required for 

 continuous cell correlation. This concept of electrical correlation natu- 

 rally assumes that some cells of the system are capable of absorbing the 

 electrical energy that is generated by other cells some distance away. 

 Whether or not coleoptile cells can absorb electrical energy will be 

 Indicated by experiments included later In this paper. 



One additional statement about the direction of auxin movement 

 must be made at this time. It Is known that the transport is from the 

 apex toward the base In the coleoptile in the vertical position. In terms 

 of the external longitudinal electrical polarity this means that the 

 transport Is toward the electropositive region of the system. 



Transverse Electrical Responses to 

 Various Types of Stimulation 



Stimulation by gravity. — The effect of stimulation by gravity on the 

 electrical field of the Avena coleoptile has been investigated extensively 

 by Schrank (23,27). His data disclose a number of changes In the various 

 electrical polarities when a plant is shifted from the vertical to the 

 horizontal position. Of these several changes only the transverse com- 

 ponent will be included in the present treatment. Figure 2 was selected 

 to show the typical results. Figure 2A shows that a transverse electrical 

 polarity in the apical portion of the coleoptile (contacts 2 millimeters 

 below the apex) Is nonexistent as long as the seedling remains In the 

 upright position. When it Is placed in the horizontal position the under 

 side becomes positive to the upper side; even the first reading, which 

 was taken one minute after the change of position, Indicates the beginning 

 of the polarity. It is worth while to note that this transverse electrical 

 change occurs all along the longitudinal axis of the coleoptile, but 

 smaller potential differences are established In the more basal regions 



