63 



On the Nature of the Galvanotropic Irritability of Roots. 

 By Alfked J. Ewaet, D.Sc., Ph.D., F.L.S., and Jessie S. Bayliss, B.Sc. 



(Communicated by Francis Darwin, For. Sec. R.S. Received September 7, — 

 Bead November 23, 1905.) 



After the contradictory statements of Elfving* that roots curve towards the 

 positive electrode (anodotropic), and of Muller-Hettlingen,f that they were 

 kathodo tropic, BrunchhorstJ apparently reconciled these contradictory observa- 

 tions by finding that strong currents, like those used by Elfving, produced a 

 curvature to the positive electrode, weak ones a curvature to the negative 

 electrode. The former curvature Brunchhorst considered to be traumatropic 

 in character, on the ground that it was shown by decapitated roots, whereas 

 the negative curvature was not. The proof that the galvanotropic irritability 

 resides solely in the root tip, is, however, quite insufficient, and hence 

 Brunchhorst's conclusion does not appear to be justified by the facts. The 

 methods of the first two investigators leave much to be desired, and although 

 Brunchhorst's experiments were, in part, carried out on a klinostat, they are 

 by no- means perfect. Thus the roots were immersed in water in a closed 

 vessel, through which the current was passed by means of carbon electrodes. 

 Apart from the effects due to the gases occluded by the electrodes, and to the 

 deficiency of oxygen in the water, there would always be a tendency for the 

 current to run obliquely or longitudinally through the roots, whose tissues 

 form better conducting media than the surrounding water. This tendency 

 will be especially pronounced when the roots are not exactly at right angles 

 to the current, as is practically always the case, and when, as in Brunchhorst's 

 experiments, numerous roots are examined at the same time. Finally, 

 although Brunchhorst gives some data as to the total amount of ourrent 

 flowing in the circuit, these data afford no evidence as to the actual amount 

 of current passing through the individual roots. Evidently, therefore, the 

 supposed positive and negative parallelo-galvanotropism of roots is by no 

 means satisfactorily established, and accordingly Miss Bayliss undertook to 

 reinvestigate this subject, under more well-defined and controllable conditions, 

 and with the results given in brief below. § 



The strength of constant current required to produce a curvature is 

 incredibly small, for using a voltage of approximately 1*3 volts, a resistance 



* ' Bot. Zeit.,' 1882, p. 257. 



+ Miiller-Hettlingen, ' Pfluger's Archhy voL 31, 1883, p. 193. 

 t Brunchhorst, ' Ber. d. D. Bot. Ges.,' 1884, vol. 2, p. 204. 

 § Full details will be given by Miss Bayliss in a later paper. 



