ELEC?PRIC RESPONSE IN PLANTS 19 
decreased by 026 volt. A second and stronger tap 
produced a second response, causing a greater diminu- 
tion of P.D. by -047 volt (fig. 6, ). The accompanying 
figure is aphotographic record of another set of response- 
curves (fig. 7). The first three responses are for a given 
intensity of stimulus, and the next six in response to 
stimulus nearly twice as strong. yi 
It will be noticed that fatigue is 
exhibited in these responses. Other 
dy 

(a) 
Fe 
é 
w 
S 
» 
2 
5 
S 
— Current of ingury 
—> action current oO 
Fic. 6.—(a) Experiment ror ExHisttiInc Exectric Response IN PLants 
BY MerHop or NecativE VARIATION. (6) Responses rn LEar-sTauKk 
or Turnip To Stimutt or Two Successive Taps, THE SECOND BEING 
STRONGER. 
A and B contacts are about 2 em. apart, B being injured. Plantis stimulated 
by a tap between A and B. Stimulus acts on both A and B, but owing to 
injury of B, effect at A is stronger and a negative variation due to differen- 
tial action occurs. 
experiments will be described in the next chapter which 
show conclusively that the response was not due to any 
accidental circumstance but was a direct result of 
stimulation. But I shall first discuss the experimental 
arrangements and method of obtaining these graphic 
records. 
Response recorder.—The galvanometer used is a 
sensitive dead-beat D’Arsonval. The period of complete 
swing of the coil under experimental conditions is about 
11 seconds. A current of 10-° ampere produces a 
c 2 
