RESPONSE OF LEAVES 239 



under-surface of the wave of true excitation, initiated 

 vertically above. This relative negativity of the under- 

 surface may or may not be helped by the induction of 

 positivity at the distal, due to the transmission of the hydro- 

 positive effect. This view is supported by the fact that in a 

 corresponding experiment on an ordinary leaf, in which the 

 second contact was at a distance too great to allow of the 

 effective transmission of any hydro-positive wave, the 

 stimulation of the upper surface induced a similar diphasic 

 response at a point diametrically opposite, on the under side. 

 In this case the second or negative component of the 

 response could not be due to anything but the subsequent 

 arrival of the true excitatory wave with its concomitant 

 negativity. 



It is now clear that among the various results 

 obtained from the study of the electrical responses of the 

 leaf of Dioncea, there are some which do not represent 

 true excitation at all, while in others it is only one of the two 

 phases which is significant of this, the other being due to the 

 hydro-positive effect. We have also seen that Burdon 

 Sanderson at starting fell into the error of wrongly identify- 

 ing the true excitatory electrical effect with that which was 

 due to the hydro-positive effect, and vice versa. We have seen 

 that there is not a single response given by the so-called 

 excitable leaf of Dioncea^ which cannot be obtained under 

 similar conditions from the leaves of ordinary plants also. 

 In fact it has been by means of experiments carried out on 

 the latter that we have been enabled to unravel all the 

 intricacies which were offered by the recorded responses of 

 the lamina of Dioncea. 



It has further been shown in the course of the present 

 chapter that the leaf and stalk currents observed in Dioncea 

 are also found in, for instance, the leaf of Ficus religiosa. 

 These have been shown, moreover, to be due to physiological 

 differences between an intermediate and the terminal points. 

 The negative variation of the leaf-current, and the positive 

 variation of the stalk -current, on the stimulation of the 



