56 



PLANT RESPONSE 



junction. From the record given below (fig. 32), it will be 

 seen that the responses are similar, even in minute details, 

 to those obtained with sensitive Biophytum leaflets. 



It will be seen that we have first the abnormal erectile 

 twitch, due to transmitted hydrostatic disturbance, which 

 takes place almost instantaneously. The true responsive 

 effect is found to follow, after an interval of four seconds. 

 From this we obtain the velocity of transmission as 75 mm. 



per second, that is to 

 say, about one-third the 

 rate found in Biopliytnm, 

 A somewhat incomplete 

 recovery took place in 

 the course of ten mi- 

 nutes. The successive 

 responses are found to 

 be nearly uniform ; but 

 if only shorter interven- 

 ing periods of rest be 

 allowed, they exhibit 

 marked fatigue. That 

 the motile region is 

 somewhere near the junction of the lamina with the petiole, 

 was proved by the fact that on bringing the stimulator 

 nearer to, or further away from, this point, the responses 

 underwent corresponding increase or diminution. 



I obtained similar responses by subjecting the lower 

 pulvinoid, that, namely, at the junction of the petiole with 

 the stem, to similar stimulus, which was now applied on the 

 adjacent stem. In the preceding experiment the Optic 

 Lever was attached to the lamina, but in this case, in order 

 to avoid possible complications from the responses of two 

 pulvinoids in succession, I tied a thin stiff wire to the inter- 

 vening portion of the petiole, and the Optic Lever was 

 attached to this wire, instead of to the lamina. By this 

 means the response of the lower pulvinoid alone was 

 recorded. 



Fig. 



32. Response of Ordinary Leaf (Arlo- 

 carpus) 



Note preliminary erectile twitch. 



