POLAR EFFECTS UNDER STRONG CURRENTS 259 



kathode was placed on the injured point, and the anode 

 at or near the pulvinus ; the exciting effect was again 

 obtained at the make of anode. The only difference in this 

 case lay in the fact that, owing to the partial loss of sensi- 

 bility at the pulvinus, the intensity of current for inducing 

 one of the higher types of response had to be increased. 



From these experiments the new types of effects. Type 

 III. and Type IV., appear to be normal. A further con- 

 sideration of this question will be postponed till I have given 

 in detail the reactions of strong currents with other species 

 of sensitive plants. 



Leaflets of Mimosa 



I have already mentioned the misgiving I at first enter- 

 tained that the somewhat unexpected appearance of excita- 

 tion at anode-make should in reality be due to transmission 

 from the distant kathodic-point. I have also described 

 the several means by which these doubts were finally set at 

 rest, one of those being previous injury of the kathodal-point 

 by scorching, in order to eliminate it as a possible source of 

 excitation. I was still desirous, however, of finding some 

 independent means of demonstrating conclusively the 

 independent character of the excitation under a strong 

 current at anode-make. 



For this purpose I found the leaflets of Mimosa eminently 

 suitable. The two bi-polar connections are made at about 

 the middle points of two different sub-petioles, care being 

 taken that the contact of each electrode is made on the 

 midrib at the insertion-points of two opposite pulvinules. 

 With this arrangement the character of excitation at anode- 

 make, whether independent or transmitted effect from the 

 distant kathode, can quite easily be discriminated, for it is 

 impossible that any excitation should be transmitted along 

 one sub-petiole to another without causing the fall of the 

 intervening leaflets. In the case of independent excita- 

 tions the fact will be displayed by the immediate fall of 



s 2 



