RESPONSIVE CURVATURE OF ANISOTROPIC ORGAN 



91 



fundamental phenomenon to be kept in mind is the greater 

 contraction of the more excitable side. This might give rise 

 to curling or uncurling, according to individual circum- 

 stances. I shall now describe 

 an experiment which illustrates 

 the opposite, or curling, action 

 of this particular form of re- 

 sponse. 



If we cut a petiole of 

 Cucurbita or a peduncle of 

 Allium corkscrew- wise, so as to 

 form a spiral strip, and pass 

 electric shocks through this 

 prepared specimen, the index 

 at its lower end shows very- 

 energetic movement, but of 

 coiling. Here we must bear in 

 mind that the inside of the 

 spiral of Passifiora has been 

 formed by the stimulus of con- 

 tact, and is thus the less excit- 

 able. Diffuse stimulation in 



such a case, therefore, will cause the contraction of the con- 

 vex surface, with the result of uncoiling. But in this spiral 

 preparation oi Allium or Cucurbita, it is theoutside which has 

 been long acted on by light, and it is the inner or concave 

 side, therefore, which remains the more excitable. Hence, 

 under stimulus, it is this more excitable inner side which 

 becomes still more concave with the result of coiling (fig. 43). 



Writhing movements of excited spiral tendril.— The 

 most striking of this series of results were obtained, however, 

 with long spiral tendrils of Passifiora, which were not too 

 old. Very strong stimuli of electric shocks were sent through 

 the entire length of these spirals, with results so striking and 

 unmistakable as to furnish a final refutation of the popular 

 assumption which distinguishes between animal and vege- 

 table tissues as relatively motile and non-motile. These 



Fk;. 43. Response by Coiling of 

 spirally-cut Alliiiiii Peduncle 



Through E and e' are passed elec- 

 trical shocks from an induction 

 coil. 



