436 



PLANT RESPONSE 



organ, by means of non-polarisable electrodes, connected, 

 one a little above, and the other a little below, the growing 

 region. According to the conditions of the experiment, the 

 balanced horizontal base-line will represent uniform growth 

 under normal turgidity. An 

 up curve will here represent a 

 rate of growth below the normal, 

 or a retardation ; a down curve, 

 on the contrary, will represent 

 a rate of growth above the 

 normal, or an acceleration. 

 When stimulus is applied a 

 responsive negative turgidity- 

 variation is induced, in conse- 

 quence of which there is a 

 temporary disturbance of the 

 balanced growth-record. The 

 curve thus produced exhibits 

 the effect of stimulus, and recovery from that effect. It will 

 be observed from the figure that on the application of tetanic 

 electric shocks for two seconds, a responsive retardation of 



Fig. 179. Photographic Record of 

 Response of Growing Style 

 of Datura alba to External 

 Stimulus 



Fig. 180. Balanced Record of Response in Growing Peduncle of 

 Eucharis Lily to Electrical Stimulation 



Up curve here represents retardation of growth. First response is to 

 stimulus of two seconds', the second to stimulus of three seconds', 

 duration. 



growth was induced, as seen in the up curve, and that there 

 was a recovery after an interval of nine minutes from the time 

 of application of stimulus. It will also be noticed that 

 during the process of recovery in this particular case, the rate 



