CHAPTER III 
ELECTRIC RESPONSE IN PLANTS—-METHOD OF 
NEGATIVE VARIATION 
Negative variation—-Response recorder—Photographic recorder—Compen- 
sator—Means of graduating intensity of stimulus—Spring-tapper and 
torsional vibrator—Intensity of stimulus dependent on amplitude of 
vibration—Eftectiveness of stimulus dependent on rapidity also. 
I swan first proceed to show that an electric response 
is evoked in plants under stimulation." 
In experiments for the exhibition of electric response 
it is preferable to use a non-electrical form of stimulus, 
for there is then a certainty that the observed response 
is entirely due to reaction from stimulus, and not, as 
might be the case with electric stimulus, to mere escape 
of stimulating current through the tissue. For this 
reason, the mechanical form of stimulation is the most 
suitable. 
I find that all parts of the living plant give electric 
response to a greater or less extent. Some, however, 
give stronger response than others. In favourable 
cases, we may have an E.M. variation as high as °1 volt. 
‘ A preliminary account of Electric Response in Plants was given at 
the end of my paper on ‘ Electric Response of Inorganic Substances * read 
before the Royal Society on June 6, 1901; also at the Friday Evening 
Discourse, Royal Institution, May 10,1901. A more complete account is 
given in my paperon ‘Electric Response in Ordinary Plants under 
Mechanical Stimulus’ read before the Linnean Society March 20, 1902. 
I thank the Royal Society and the Linnean Society for permission to 
reproduce some of my diagrams published in their Proceedings.—J. C. B. 
C 
