24 RESPONSE IN THE LIVING AND NON-LIVING 



The electric tapper. Instead of the simple mechanical 

 tapper, an electromagnetic tapper may be used. 



Vibrational stimulus. I find that torsional vibration 

 affords another very effective method of stimulation 

 (fig. 11). The plant-stalk may be fixed in a vice (v), the 

 free ends being held in tubes (c c'), provided with three 

 clamping jaws. A rapid torsional vibration 1 may now 

 be imparted to the stalk by means of the handle (H). 

 The amplitude of vibration, which determines the 

 intensity of stimulus, can be accurately measured by 



FIG. 11. THE TORSIONAL VIBRATOR 



Plant P is securely held by a vice V. The two ends are clamped by holders 

 C C'. By means of handles H H', torsional vibration may be imparted to 

 either the end A or end B of the plant. The end view (6) shows how the 

 amplitude of vibration is predetermined by means of movable stops S S'. 



the graduated circle. The amplitude of vibration may 

 be predetermined by means of the sliding stops (s s'). 



Intensity of stimulus dependent on amplitude of 

 vibration. I shall now describe an experiment which 

 shows that torsional vibration is as effective as stimula- 

 tion by taps, and that its stimulating intensity increases, 

 length of stalk being constant, with amplitude of 



. a By this is meant a rapid to-and-fro or complete vibration. In order 

 that successive responses should be uniform it is essential that there should 

 be no resultant twist, i.e. the plant at the end of vibration should be in 

 exactly the same condition as at the beginning. 



