322 LECTURE XIV. 



tricity, or whether they are due to purely physical causes. 

 Buff considers them to be quite independent of the vital 

 processes of the plant, and in this opinion Jiirgensen, Heiden- 

 hain, and Ranke agree. Kunkel offers the following expla- 

 nation of the phenomena. He ascertained, by a number of 

 experiments of different kinds, that whenever a current of 

 water is set up between one part of an organ and another, it 

 is accompanied by a disturbance of electrical equilibrium of 

 such a nature that a current travels (through the galvanometer) 

 in the same direction as that in which the current of water is 

 travelling. Let us consider one case from this point of view. 

 In speaking of Munk's experiments it was mentioned that all 

 points on the mid-rib of the leaf of Dionsea are positive as 

 compared with all points on the lamina, and Kunkel found 

 this relation to hold in the considerable number of leaves of 

 dicotyledonous plants which he investigated. Now it is well 

 known that the nervature of leaves is more easily wetted by 

 water than the rest of the surface. When, then, a moist 

 non-polarisable electrode is placed on a nerve and another on 

 the surface of the lamina, the point of the nerve touched by 

 the electrode will become moist more rapidly than the point 

 of the surface, and diffusion-currents will be set up which are 

 more active at the one point than at the other: these diffusion- . 

 currents are accompanied by electrical disturbances, as is 

 well known in Physics, and the result is a difference of elec- 

 trical potential at the two points which is indicated by a 

 current passing from the former to the latter through the 

 galvanometer with which the electrodes are connected. We 

 can apply this explanation to the above-mentioned results of 

 Buff, Jiirgensen, Heidenhain, and Ranke. The greater the 

 amount of water present in a mass of tissue the less active 

 will be the diffusion-currents when water is placed on its 

 surface, and the less considerable will be the accompanying 

 electrical disturbance. In the experiments with roots, the 

 root had been previously well washed in water, so that it was 

 saturated ; hence, when the moist electrode was laid upon it, 

 or when, as in Buff's method, the root was dipped in water, 

 the diffusion-currents set up were less active than those set 



