64 Dr. A. J. Ewart and Miss J. S. Bayliss. On the [Sept. 7, 



of 100,000 to 150,000 ohms was required in the circuit, so that the current 

 passing through the 1 to 3 sq. mm. of cross-section lay between O'OOOOlSo 

 and 0-000009 of an ampere. Even then it was difficult to produce a curva- 

 ture without serious injury, or even fatal effects in the case of sensitive roots. 

 When the platinum electrodes were on opposite sides of the apex, the curva- 

 ture was always towards the positive electrode. If, however, one electrode 

 was placed on the non-irritable base of the root and the other to one side 

 of the apex, the curvature always took place towards the current side, inde- 

 pendently of which electrode was on the apex. These results were obtained 

 upon a klinostat into which the current was led by mercury contacts, and 

 transmitted by platinum electrodes to the stimulated region of the root. 

 The seedling and wires within the rotating glass cylinder were insulated on a 

 slab of paraffin wax. 



The facts observed suggested that the curvatures were not the result of 

 any parallelo-galvanotropic irritability, but were due to the accumulation of 

 the products of electrolysis at the points of application of the electrodes. 

 Confirmation was obtained by exposing the roots to strong currents (voltage 

 1 to 4) for short periods (five to eight minutes), and then rotating on a 

 klinostat, when exactly similar results to the above were given. Furthermore, 

 if the anodal region was cut out of an electrolysed root and applied to one 

 side of the apex of another, a curvature was shown to this side. In addition, 

 the application of minute squares of absorbent paper, moistened with 

 decinormal acid or alkali, caused curvatures towards the stimulated side, 

 whereas ordinary neutral paper produced no effect in air saturated with 

 moisture. When the acid and alkali were applied simultaneously on opposite 

 sides, the curvature always took place towards the acid side. This corresponds 

 to the curvature towards the positive (acid) electrode produced by moderately 

 strong currents. The weakest currents used produced similar positive curva- 

 tures, and hence Brunchhorst's negative curvatures cannot be explained 

 by Weber's law, as being due to the normal acidity of the root tissues 

 preventing the stronger stimulating action of the acid coming fully into play 

 until it accumulates beyond a certain limit. 



The curvatures are usually completed in from 6 to 24 hours after exposure 

 to the current, but they may be distinctly perceptible within four to six 

 hours, and may begin in one to two hours, under optimal conditions. Hence 

 it is not surprising that if the roots are fixed in a plaster east after stimula- 

 tion, and rotated on a klinostat for one or two days, a rapid sharp curvature 

 is produced on freeing the root from the cast, whereas after two to four days 

 the effect of the stimulation has passed away. All of these curvatures can be 

 produced without any of the cells of the root being killed, and even when an 



