98 CHAP. X. EFFECT OF MECHANICAL STIMULATION 



The extent of the maximum movement was measured 

 by the microscope-micrometer. The following results were 

 obtained with four different specimens : 



* 



Table XIII. — Showing the Relative Intensities of Response of 

 THE Upper and Under Sides of the Tendril (Passiflora). 



The upper side of the tendril is therefore not entirely devoid 

 of moto-excitability, its power of contraction being about 

 one-seventh that of the under side. 



Inhibitory Action of Stimulation 



The following puzzling phenomenon was observed by 

 Fitting in tendrils w^hich are specially sensitive on the under 

 side : 



' If a small part of the upper side and at the same time 

 the whole of the under side be stimulated, curvature takes 

 place only at the places on the under side which lie opposite 

 to the unstimulated regions of the upper side. The sensitive- 

 ness to contact is thus as well developed on the upper side 

 as on the under side, and the difference between the two 

 sides lies in the fact that while stimulation of the under 

 side induces curvature, stimulation of the upper side induces 

 no visible result, or simply inhibits curvature on the under 

 side, according to circumstances.' ^ 



It certainly seems to be anomalous that one side of the 

 organ, apparently inexcitable, should inhibit the response of 

 the opposite side. The results of my experiments already 

 described afford a satisfactory explanation of this curious 

 phenomenon of inhibition. 



^ Jost, Lectures on Plant Physiology, trans, by R. J. Harvey Gibson, 

 p. 490 (Clarendon Press). 



