32 COMPARATIVE ELECTRO-PHYSIOLOGY 



Moistened cotton threads in connection with the non-polari- 

 sable electrodes, E E, make secure electrical contacts with A 

 and B. For experimenting on the effects of temperature, 

 there is an electrical heating coil, R, inside the chamber. 

 For the study of the effects of different gases, there are inlet 

 and outlet tubes, which enable a stream of the required gas 

 or vapour to be circulated through the chamber. 



If the A end of the specimen be now suddenly torsioned 

 through a given number of degrees, a responsive electro- 

 motive variation takes place, which after- 

 wards subsides gradually. If next the 

 torsioned end be suddenly brought back 

 to the original position, a second electro- 

 motive response is obtained, similar to the 

 first. Hence, in the case of a to-and-fro 

 cu b c fl vibration, the responsive effects are addi- 

 tive, and we have the further advantage 

 FIG 22 Influence of that the tissue at the end of the operation is 

 Suddenness on the 



Efficiency of Stimu- returned to its original physical condition. 

 In order that successive stimuli may 



The curves a, b, t, d, . 



are responses to be equally effective, another factor besides 

 vibrations of the ^g constancy of the amplitude of vibra- 



same amplitude, 



30. In a the vi- tion has to be considered. It is to be 

 borne in mind that the effectiveness of the 



was 



less slow ; it was stimulus in evoking response depends also 



rapid in c, and very , ... r . r . .. 



rapid in d. on tne rapidity of the onset of the dis- 



turbance. In the application of vibratory 

 stimulation to plants, I find the extent of response to depend 

 to some degree on the quickness with which the vibration 

 is effected. I give below records of responses to successive 

 stimuli, induced by vibration through the same amplitude, 

 which were delivered with increasing rapidity (fig. 22). It 

 will be noticed that an increasing quickness of vibration 

 increased the response, but that this reached a limit. If 

 we wish, then, to maintain the effective intensity of stimulus 

 constant, we must meet two conditions. First, the amplitude 

 of vibration must be kept the same. This is done by means 



