144 RESEARCHES ON IRRITABILITY OF PLANTS 



taken with the original feeble stimulus -intensity of -5. 

 It will be seen from the third record that the time taken 

 for the transmission of excitation was practically the same 

 as that with the previous strong stimulus, showing that 

 this has made the tissue better conducting and that this 

 property has reached a limit of uniformity. In order to 

 test this conclusion further, a fourth record was taken 

 with the second high stimulus-intensity of 4. It will be 

 observed that the time of transmission is now the same as 

 with the feebler intensity. 



From these experiments it will be understood that when 

 the tissue is in a somewhat sluggish or sub-tonic con- 

 dition the velocity of transmission is enhanced under 

 increasing intensity of stimulation. This, however, reaches 

 a limit under a maximal stimulus the value of which is 

 about 3 units. The following table gives the results of two 

 sets of experiments on the effect of increased intensity of 

 stimulus on velocity : — 



Table I. — Effect of Intensity of Stimulus on Velocity in 

 Sub-tonic Specimens. 



The fact that stimulus itself may enhance conductivity 

 in a sub-tonic tissue can be seen in a striking manner 

 in specimens of Mimosa which are in sluggish condition. 

 It will there be found that the application of stimulus on 

 the petiole will at first fail to be conducted. If, however, 

 we apply the same stimulus again after the usual interval 

 of, say, 15 minutes, the excitation which failed in the pre- 

 vious case to be conducted will then reach the pulvinus 



