A. R. SCHRANK 139 



some of its effects by inhibiting the movement of the active auxin (32). 

 This explanation, however, is inadequate to account for the inhibition 

 of the phototropic bending by current appHed longitudinally to the 

 illuminated side. Furthermore, the data that are available (14) indicate 

 that the inhibition of streaming is independent of the polarity of the 

 applied current, while many of the experiments which have been re- 

 viewed in this paper show that the magnitude and temporal sequence of 

 the curvature of the coleoptile in response to current are dependent on 

 both the polarity and strength of the electrical stimulation. It is obvious 

 that protoplasmic streaming, at best, can play only a limited role in 

 these electrically induced growth phenomena. 



A number of experimental observations that have been presented 

 would permit the possibiHty of accepting the inherent electrical field 

 as the primary integrating mechanism of the Avena coleoptile. 1) In 

 stimulation by light, gravity, or mechanical means the electrical polarity 

 changes apparently precede the hormone redistribution and curvature. 



2) The orientation of the transverse polarity with reference to the 

 direction of the subsequent bending is consistent in all of these instances. 



3) Experimental evidence has been presented to show that the inherent 

 electrical field of the coleoptile is not dependent on the same auxin- 

 controlled process that is required for elongation. 4) Cells of the 

 coleoptile are capable of absorbing electrical energy; this is demonstrated 

 by the fact that curvature can be induced by either transversely or 

 longitudinally appHed current. These growth responses in every instance 

 are dependent on the polarity of the applied current. 5) Additional 

 evidence indicates that applied current induces its effect on growth via 

 the same mechanism that unilateral illumination does; at least both are 

 limited by a common factor. 



Obviously the summarized facts are still inadequate to prove con- 

 clusively that the inherent electrical field functions as the primary 

 correlating mechanism in the Avena coleoptile. It Is now certain that an 

 externally imposed electrical field does affect the growth of the coleoptile 

 in a polar fashion, but much more Information is needed to clarify the 

 details of this relationship. Additional data are also necessary to account 

 for the fact that the coleoptile bends toward the electropositive pole of 

 the current-applying circuit, while in the remainder of the troplsms the 

 curvature is away from the positive side of the plant. 



