BLECTRIC.. 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 
described in the next few chapters 
will show, they furnish an accurate 
index of physiological activity. For 
it will be found that, other things 
being equal, whatever tends to exalt 
or depress the vitality of the plant 
tends also to increase or diminish 
These E.M. 
effects are well marked, and attain 
its electric response. 
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 

Fic. 15.—REsponsE IN 
PuantT (FROM THE 
SrimuLATED A To Un- 
STIMULATED B) com- 
PLETELY IMMERSED 
UNDER WATER 
The leaf-stalk is clamped 
securely in the middle 
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 currentof response is 
found to flow in the 
stalk from the excited 
A to the unexcited B, 
and outside, through 
the liquid, from B to A. 
A portion of this cur- 
rent, flowing through 
the side tubes ¢ t’, pro- 
duces deflection in the 
galvanometer. 
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 
