RESPONSE OF LEAVES 



229 



was chiefly carried out by means of experiments on electrical 

 variations induced in the lamina. These depended (i) on 

 variations in the cross-difference of existing potential between 

 the upper and lower surfaces, according to his ' fundamental 

 experiment/ and (2) on electrical variations in the led-offs of 

 symmetrical surfaces of contact on the under-side of opposite 

 lobes. The results which he obtained, however, by these 

 methods, appear to the reader to have been very conflicting, 

 and in fact the experimental methods described by him 

 would seem to have been open to many sources of complica- 

 tion of which he himself was unaware. 



FIG. 148. Burdon Sanderson's Funda- 

 mental Experiment on Diomca Leaf 



Electrical stimulus applied on distal 

 lobe, 7, induces responsive effect 

 on led-off circuit fm. Upper or 

 internal surface, /, more excitable 

 than lower, m. 



FIG. 149. Parallel Experiment in 

 Sheathing Petiole of Musa 



Thermal stimulus applied on distal 

 side induces responsive effect on 

 led-off circuit. Upper or 'internal' 

 surface more excitable than lower. 



I shall deal first with Burdon Sanderson's ' fundamental 

 experiment/ of which the excitatory electrodes are seen on the 

 left lobe, and the led-off on the right in fig. 148. In fig. 149 

 is given a diagram of a parallel experiment carried out by 

 myself on the petiole of Musa. According to Burdon- 

 Sanderson, as the result of excitation, a t current is induced 

 in the right lobe of Dioncea (fig. 150). This means, of 

 course, that the upper or more excitable surface of the right 

 lobe has become positive to the lower. This current, how- 

 ever, he termed * excitatory/ regarding it as the analogue of 

 the 'action-current' known to animal physiology. After 

 this first phase, when a certain interval had elapsed, he 



