THE POSITIVE RESPONSE 



i85 



place 14 seconds, and the true excitatory effect 48 seconds, 

 after the application of the stimulus (fig. 99). 



In an experiment where the chemical mode of stimu- 

 lation was employed, the distance to be traversed was 

 40 mm. The positive impulse reached the responding leaflet 

 19 seconds, and the negative impulse 50 seconds, after the 

 application of the stimulus. 



Thermal stimulus was applied in another experiment 

 at a distance of 70 mm. The transmission periods for 

 the positive and negative impulses were 22 seconds and 

 65 seconds respectively. 

 The negative impulse 

 thus lagged behind the 

 positive by as much as 

 43 seconds. 



Mimosa pudica. — It 

 was stated that in speci- 

 mens like the petiole of 

 Mimosa, where the velo- 

 city of transmission of 

 excitation was high, the 

 positive response was 

 liable to be masked by 

 the predominant nega- 

 tive. It is therefore only 

 on rare occasions that 



I obtained a positive response by stimulating the petiole 

 of Mimosa. This is seen in fig. 100, where stimulus of 

 induction-shock was applied at a point on the petiole 

 30 mm. from the responding pulvinus. The Resonant 

 Recorder having a long writing-index was employed for 

 obtaining the record. The vibration-frequency of the writer 

 was five times in a second, hence successive dots represent 

 time-intervals of *2 second. It will be seen that the 

 positive response took place *6 second and the negative 

 3*2 seconds after the application of the stimulus. 



It was stated that, by applying stimulus at a sufficient 



Fig. 100. — Records showing positive 

 response in Mimosa followed by 

 negative. Stimulus was applied on 

 the petiole 30 mm. from pulvinus. 

 Vibration-frequency 5 per second. 



