THE POSITIVE RESPONSE i8i 



was taken by means of the Oscillating Recorder, the fre- 

 quency of oscillation being once in a second. Successive 

 dots are thus at intervals of a second. In the experiment, 

 the record of which is given in fig. 96, stimulus was applied 

 on the petiole at a distance of 50 mm. from the responding 

 leaflet. It is seen from the record that in answer to the 

 stimulus two distinct responses of opposite signs occurred 

 in succession. The positive or erectile response (repre- 

 sented by down curve) is seen to have occurred 1*5 second 

 after the application of the thermal shock ; the excitatory 

 or negative response took place much later, that is to say, 

 22 seconds after the shock. The velocity of the positive 

 impulse is here 33 mm. per second, that of the negative 

 being 2*3 mm. per second. 



From the experiment just described it is clear that a 

 single stimulus gives rise to two impulses, positive and 

 negative. The positive travels at a faster rate and gives rise 

 at the responding-point to the erection of the leaflet indi- 

 cative of positive turgidity variation. The negative or the 

 excitatory impulse travels at a slower rate, inducing at the 

 responding organ negative turgidity variation, contraction, 

 and the fall of leaflet. 



It was stated that the transmission-time is relatively 

 long when stimulus is applied on the stem instead of on the 

 petiole. This will be seen clearly from the results of experi- 

 ments which I shall now describe. Thermal stimulus was 

 first applied on the stem, the distance of the responding 

 leaflet being 10 mm. of stem and 20 mm. of petiole. The 

 positive response took place 3 seconds and the negative 

 21 seconds after the application of the thermal shock. 

 Stimulus was next applied on the petiole at a distance of 

 20 mm. Had the velocity of transmission in the stem and 

 the petiole been the same, then the negative impulse would 

 have reached the leaflet after an interval of f^ X 21 seconds 

 or 14 seconds. Instead of this, the transmission-period 

 in the petiole was found to be much shorter — namely. 



