BLECTRIC RESPONSE IN. PLANTS ° ~ 21 
as long as the plant rests unstimulated, the pen, remain- 
ing coincident with the stationary galvanometer spot 
on the revolving paper, describes a straight line. If, on 
stimulation, we trace the resulting excursion of the spot 
of light, by moving the carrier which holds the pen, the 
rising portion of the response-curve will be obtained. 
The galvanometer spot will then return more or less 
gradually to its original position, and that part of the 
curve which is traced during the process constitutes the 
recovery. ‘The 
ordinate in these 
curves repre- eee 
sents the E.M. sas 
variation, and 
the abscissa the 
time. 
We can cali- 
brate the value 
of the deflection 
by applyme a 
known E.M.F. to the circuit from a compensator, and 
noting the deflection which results. The speed of the 
clock is previously adjusted so that the recording surface 
moves exactly through, say, one inch aminute. Of course 
Fic. 8.—REsponsE RECORDER 
this speed can be increased to suit the particular experi- 
ment, and in some it is as high as six inches a minute. 
In this simple manner very accurate records may be 
made. It has the additional advantage that one is able at 
once to see whether the specimen is suitable for the pur- 
pose of investigation. A large number of records might 
be taken by this means in a comparatively short time. 
