vi ELECTROMOTIVE ACTION IX VEGETABLE CELLS 



and tiexion on the development of differences of potential. On 

 leading oft' from two points of a green stern which is in itself 

 isoelectric, a P.D. always appears when the vicinity of one 

 electrode is injured (by cutting or squeezing), that electrode 

 being invariably negative to the other. The same occurs on 

 bending the stalk, if this is effected by a sudden jerk. Slow, 

 regular liexion, on the contrary, produces no effect on the 

 galvanometer. The electrodes were prevented, by threads, from 

 shifting along the stalk. 



The theoretical conclusion from these experiments (which were 

 subsequently confirmed by 0. Haake, 5) was, like Griinhagen's 

 theory of the manifestations of animal electricity, referred to the 

 so-called diaphragmatic currents, nor did it obtain longer than the 

 former once more proving that it is not sufficient, in explana- 

 tion of a physiological phenomenon, to bring forward a single, 

 purely physical, symptom, but that we are in presence of a vital 

 manifestation, the intrinsic character of which is determined by 

 a complex interaction of physical and chemical forces. 



In the " migration of water " Kunkel believed that he had 

 discovered an infallible, and universally applicable, key to the 

 electrical phenomena which may at times be observed in vegetable 

 organs. In the case of his fundamental experiment with green 

 leaves, he ascribes the observed differences in potential to the 

 differing resistance presented by the tissues, at the leading-off 

 contacts, to the water, which diffuses inwards from the moist 

 electrodes, thus bringing about the requisite movement of water. 

 And indeed the unequal moisture of the ribs and mesophyll is 

 an easily-verified fact in many leaves. But, as Haake points 

 out, the leaf may be sponged over, or covered permanently with 

 water, without alteration of the electromotive reaction. Even 

 more convincing is the reaction of permanently submerged 

 leaves ( Vallisneria, Nitella), " from -which regular currents can 

 be led off even when they lie under water (to the depth of -| 1 

 mm.)." Haake further remarks " that a normal electrical reaction 

 is exhibited only in the living leaf. A leaf killed by momentary 

 immersion in boiling water gives no more reaction if left one to 

 two days in the moist chamber, than a leaf that has died 

 naturally, and yet the conditions for quantitative differences in 

 the migration of water are still present." 



And against the validity of the " drop experiment " Haake 



