RESPONSE OF LEAVES 



233 



The suggestion, therefore, that the reversal of response is 

 due, in some way unexplained, to a reversal of the electrical 

 condition of the leaf, cannot hold good. Nor does the use of 

 the term * modification ' in any way assist in the elucidation 

 of the phenomenon. A satisfactory 

 explanation of this reversal of 

 response, then, still remains to be 

 found. 



So much for the 'fundamental 

 experiment' The next experi- 

 mental arrangement employed by 

 Burdon Sanderson consists of a leaf 

 which is led off by symmetrical 

 contacts on the under surfaces of 

 its two lobes (fig. 153). If now the 

 right lobe was excited, by touching 



one of the sensitive filaments (on the upper surface) with a 

 camel's-hair pencil, in the neighbourhood of the leading-oft 

 contact, it was found that the under-surface of the right lobe 

 became first positive, and subsequently negative (fig. 154), 

 relatively to the left (ibid. p. 440). 



FIG. 153. Experimental Con- 

 nections with Dionaa ac- 

 cording to the Second 

 Experimental Method of 

 Burdon Sanderson 



FIG. 154. Response of Under-surface of Leaf of Dioncea, with Electrical 

 Connections as in Fig. 153 



Mechanical excitation of upper surface of right lobe shows relative 

 positivity of under surface of same right lobe (up curve), followed by 

 its relative negativity (down curve). Time-marks 20 per second 

 (Burdon Sanderson). 



Summarising these various observations, then, we find 



results which are very much at variance. First, according 



to the ' fundamental experiment,' certain leaves are seen to 



give rise to the positive response ; other leaves, in their 



prime/ give diphasic response, the upper surface becoming 



