1905.] Nature of the Galvanotropic Irritability of Roots. 65 



injury is produced, the curvature is usually towards the injured side, instead 

 of away from it, as in a true traumatropic curvature. 



The curvatures produced by continuous currents appear usually to be 

 accompanied or preceded by a temporary more or less pronounced retardation 

 of the average rate of growth in length. Indeed the latter may be temporarily 

 arrested for some time after strong stimulation, even when the electric current 

 produces little or no injury. In such cases negative results may be obtained 

 as regards curvature. 



Finally, using non-polarizable electrodes moistened with cell- sap diluted 

 with distilled water, no curvatures were produced, whereas similar stimulation, 

 using platinum electrodes applied to the surface of the root, and with the 

 non-polarizable electrodes still in the circuit so that the resistance was the 

 same, gave the usual curvatures according to how and where the electrodes 

 were applied. With stronger currents and more prolonged exposure, curva- 

 tures are induced, even when " non-polarizable " electrodes are used, since the 

 products of electrolysis may diffuse to the surface of the root, and it is 

 impossible to prevent the internal polarization which takes place wherever the 

 current traverses dissimilar saline solutions separated by semi-impermeable 

 membranes. There is, however, less tendency to injury than with platinum 

 electrodes. 



The irritable and responsive zone extends 4 to 5 mm. behind the apex of 

 the root of Vicia Fata and Phaseolus vulgaris. When one platinum electrode 

 was applied to the non -irritable base of a root, and the other laid flat on the 

 extreme tip, no curvature was produced in whichever direction the current 

 was passed. This is presumably due to the products of electrolysis diffusing 

 evenly and stimulating the irritable regions and cells equally on all sides, for 

 when the same current was applied transversely behind the apex, a positive 

 curvature was shown. If the roots were either truly positively or truly 

 negatively parallelogalvanotropic, they should curve in the above experiment 

 so as to place the tip parallel to the current, and either against or with its 

 direction, whenever this does not at first coincide with their tropic 

 irritability. 



The " galvanotropism " of roots is therefore due to chemotropic stimulation 

 by the products of electrolysis, of which the acid is more effective than the 

 alkali, the latter also being neutralised more or less by the respiratory carbon 

 dioxide. It is indeed possible that the curvature of the roots of Lupinus 

 alius in gelatine towards phosphates and carbonates observed by Lilienfeldt* 

 may be of similar origin, since acid phosphate and alkaline carbonates were 

 used. That the " galvanotropic " or galvanogenic curvatures are not trauma- 

 * Lilienfeldt, 'Ber. d. D. Bot. Ges.,' 1905, vol. 23, p. 91. 

 VOL. LXXV1I. B. F 



