ELECTRIC 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- 

 sents the E.M. 

 variation, and 

 the abscissa the 

 time. 



We can cali- 

 brate the value 

 of the deflection 

 by applying 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 a minute. Of course 

 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. 



FIG. 8. EESPONSE KECORDER 



