VELOCITY OF TRANSMITTED IMPULSE 145 



and induce the responsive fall. Stimulus had thus imparted 

 conductivity to the tissue. 



Effect of Optimum Condition 



We have seen that when the tissue is in a favourable 

 tonic condition the range between minimal and maximal 

 excitation tends to vanish— that is to say, a moderately 

 feeble stimulus induces the same amplitude of response 

 as the maximal. It appears probable that what was 

 found to be true in the case of motile excitability may be 

 equally appHcable to conductivity ; that velocity of trans- 



FiG. 86. — Effect of optimum condition on velocity. Plant raised to tem- 

 perature 30° C. ; records taken under stimulus -5 (lowest), 2 (highest), 

 •5 once more (middle). Velocity practically the same. 



mission will tend to be constant, even under varying in- 

 tensity of stimulus, when the tissue is in a favourable tonic 

 condition. 



In order to test this induction I next tried the effect 

 of varying intensity of stimulus on a specimen which had 

 been brought to a favourable tonic condition. We have 

 already noticed how the excitability of the plant is enhanced 

 when the surrounding temperature is raised to 30° C. or 

 thereabouts. This was secured by enclosing the experimental 

 plant in a thermal chamber, which was maintained at the 

 uniform temperature of 30° C. The point of stimulation 



