CHAPTEE 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 Effectiveness of stimulus dependent on rapidity also. 



I SHALL first proceed to show that an electric response 

 is evoked in plants under stimulation. 1 



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. 



1 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 paper on * 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. 0. B. 



C 



