Polarization and Stimulation of the Onion Root by Direct Current.

Previous work has shown (1) that the passage of a constant, positive electric current through an onion root (a) increased the positivity of the observed' electric potential when the current was sent up the root (polarization) and (b) decreased the observed potential when the current was sent down the root (depolarization). This confirmeds earlier observations by MARSH (11) and was in agreement with similar experiments by WILKS (19) and CLARK (8) with the Avena coleoptile, ROSENE (17) with the Douglas fir, and REHM (15) with Phaseolus multiflorus. This effect was due to changes within the root and not at the contacts. The magnitude of the change was greater when the potential was decreased than when it was increased. Moreover, basal segments of the root exhibited smaller responses to a given current flow than apical segments. Both hydrogen cyanide and hydrogen redueed the inherent electric potential to essentially zero and at the same time produced little, if any, change in the action of applied current. These effects were reversible. The minimum current required for producing (a) or (b) was well within the range of current magnitude that could be maintained by the root in an external circuit. It was higher in basal segments than in apical segments. With constant current applied for increasing time periods, the effect reached a maximum. These results were interpreted as being due to an ionic accumulation at "phase boundaries" within the cell. This potential due to polarization was shown to be independent of inherent potential. Several "anomalous" curves (1, fig. 9) were obtained, however, in which there was a decrease with upward current in contrast to (a) above, and it was thought that the current acted as a stimulus for the root with a resultant negativity in inherent P.D. similar to an effect produced by MARSH (12) mechanically in the onion root. REHM (15) also found such a change but only when the applied current was several fold larger than that required for polarization. In a series of studies on the effect of applied direct current on the potentials of the coenocytic algae, BLINKS (4, 5, 6) found that currents opposing the inherent flow increased the P.D. while series currents decreased the P.D. He was able, however, to show that with increased opposing current a stimulated condition could be produced in which the potential decreased rather than increased. The ease with which this effect could be obtained was subject to the previous history of the cells, particularly the ionic constituents of the medium in which they were kept. ' The usual convention is to measure the electric potential of the distal contact with respect to the earthed proximal contact.