RESPONSIVE CURVATURE OF ANISOTROPIC ORGAN 87 



the hollow petiole of Cucurbita or the peduncle of Allium. 

 Of these two specimens, the latter is the more sensitive, and 

 reacts far more quickly. It will be observed that the out- 

 side of such tubular organs growing erect has been long 

 exposed to light, whereas the inside has been protected from 

 it. If we now split the specimen for a few centimetres of its 

 length, then the freed halves, owing to the differences of 

 tension as between the 

 outside and inside, will be 

 found to curve outwards, 

 that is to say, the inner 

 side becomes convex. In 

 the previous experiments, 

 where the two halves were 

 rejoined, anisotropy having 

 been induced, we observed 

 the effect of the relatively 

 greater contraction of one 

 of the two halves. But we 

 are now about to study 

 natural differences of ex- 

 citability as between the 

 inner and outer surfaces of 

 each half. As the outer 

 surface has already been 

 exposed to the continuous 

 action of stimulus of light, 



Fig. 41. Response of Bifurcated Allium 



Tube by sudden Collapse 

 E and e' are connected with induction 



coil, by means of which the plant is 



stimulated electrically. 



we should expect the inner or protected side to be relatively 

 the more excitable. The effect of diffuse stimulus should 

 then be to straighten the curled halves, by producing a 

 greater contraction of the more excitable inner side, which 

 is at present convex. The experiment is carried out by 

 dipping the freed ends in a beaker of water, the undivided 

 portion being held in a clamp (fig. 41). Electrical con- 

 nections are made with the upper part, and with the water 

 in the beaker in which the free ends of the specimen are 

 dipped. After passing a few shocks from an induction coil 



