5i8 



PLANT RESPONSE 



galvanometric negativity, thus proving that the strong 

 excitatory effect transmitted to the organ had not only 

 neutralised, but also reversed, the previous effect (fig. 215). 



2. Direct unilateral stimulation of • growing region : 

 Moderate/y strong stimulus. — When stin:iulus is applied near 

 the responding organ, say at C (fig. 212, a\ there is always 



Fig. 215. Record showing Neutralisalion 

 and Reversal of Electrical Response 

 at Responding Region, under Strong 

 Stimulation of Tip 



This indicates that the first positive turgidity- 

 variation, due to indirect stimulation, is 

 converted into negative turgidity-varia- 

 tion of transmitted true excitation. 



Fig. 216. Record showing 

 Negative Electrical Re- 

 sponse represented by Up 

 Curve, indicating Negative 

 Turgidity - Variation due 

 to Direct Stimulation 



produced at A a negative electrical, indicating a negative 

 turgidity, variation (fig. 216). 



Thus we have obtained, using the same moderate stimulus, 

 two opposite effects, of positive and negative turgidity-varia- 

 tions, according as the point of application was at the distant 

 tip or in the vicinity of the responding organ. It is evident, 

 moreover, that there is a continuity between these two 

 extreme effects, for, as we gradually shift the point of applica- 

 tion from the distant point nearer to the responding organ 

 we observe corresponding intermediate changes, from pure 

 positive, through the neutral, due to equal positive and 

 negative effects, to pure negative. 



