ELECTRIC RESPONSE IN PLANTS 



29 



block method which has just been described, there is 

 no injury, the plant is normal throughout, and any 

 physiological change (which in plants will be exceedingly 

 small during the time of the experi- 

 ment) will affect it as a whole. 



Plant response a physiological or 

 vital response. I now proceed to a 

 demonstration of the fact that what- 

 ever be the mechanism by which 

 they are brought about, these plant 

 responses are physiological in their 

 character. As the investigations 



, FIG. 15. BESPONSE IN 



described in the next few chapters PLANT (FKOM THE 



.,, , , . ^ STIMULATED A TO UN- 



Will show, they lurnisn an accurate STIMULATED B) COM- 



index of physiological activity. For T Wi "" 

 it will be found that, other things The leaf-staik is damped 



securely in the middle 



being equal, whatever tends to exalt 

 or depress the vitality of the plant 

 tends also to increase or diminish 

 its electric response. These E.M. 

 effects are well marked, and attain 

 considerable value, rising sometimes, 

 as has been said before, to as much 

 as *1 volt or more. They are pro- 

 portional to the intensity of stimulus. 

 It need hardly be added that 

 special precautions are taken to 

 avoid shifting of contacts. Variation 

 of contact, however, could not in any case account for 

 repeated transient responses to repeated stimuli, when 

 contact is made on iso-electric surfaces. Nor could it 



with the cork C, inside 

 the tube T, which is 

 filled with water, the 

 plant being completely- 

 immersed. Moistened 

 threads in connection 

 with the two non-polar- 

 isable electrodes are 

 led to the side tubes 

 tt'. One end of the 

 stalk is held in ebonite 

 forceps and vibrated. 

 A current of response is 

 found to flow in the 

 stalk from the excited 

 A to the unexcited B r 

 and outside, through 

 the liquid, from B to A. 

 A portion of this cur- 

 rent, flowing through 

 the side tubes 1 1', pro- 

 duces deflection in the 

 galvanometer. 



