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’ 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 
(6) 




Fic. 11.—TuHer Torstonat VIBRATOR 
Plant P is securely held by a vice V. The two ends are clamped by holders 
CC’. 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 (0) 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 (ss’). 
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 
2 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. : 
