1901.] on the Response of Inorganic Matter to Stimulus. 623 



3. Or, taking again an unblocked stalk, let one contact be made 

 in the usual manner at the end A, and the other at the end B, which 

 is now injured by a cut (see Fig. 7). There will now be a per- 

 manent difference of electric level between the two ends, and a cur- 

 rent of injury will be found to flow through the stalk from the 

 injured to the uninjured. This contact at the injured end may be 

 made in a very simple manner by passing a strip of moistened cloth 

 through a slit in the stalk at B. Or, better still, instead of the cut 



Fig. 6. — Response in plants by block 

 method and response curves. C, clamp or 

 block. Stimulation of A end produces 

 current in one direction, that of B end in 

 opposite direction, as shown by curves 

 given in (a). In (b) is shown abolition of 

 response in B half when killed. 



Fig. 7. — Response in plants — 

 negative variation. There is a 

 resting current owing to injury at B. 

 Stimulation produces a diminution 

 of this resting current, as shown iu 

 (c). The dotted line represents 

 the galvanometer zero. 



we may use a few drops of strong KH.0 solution, to injure the B end. 

 If now the stalk be subjected to mechanical stimulus, it will be 

 found that there is a responsive negative variation, or a diminution 

 in the original current of rest (c, Fig. 7). 



Thus we see that under stimulation the plant, like muscle or nerve, 

 is thrown into an excitatory state of which the electrical change is 

 the concomitant, this electric response being regarded by physiolo- 

 gists as proof of the living condition of the substance. 



4. But how can we be certain that this electrical indication is 

 peculiar, sui generis, to the physiological or living state ? The crucial 



