TWINING OP TENDRILS 297 



the impulses, positive and negative. This is seen illustrated 

 in figure 100, where the rigid stem of Mimosa was subjected 

 to unilateral stimulation ; the effect of indirect stimulus was 

 found to induce an enhancement of turgor at the diametri- 

 cally opposite side, and thus caused an erectile movement of 

 the motile leaf. Electric investigations which I have carried 

 out also corroborate the results given above. Here also 

 stimulation of a non-motile organ at any point, induces 

 at a diametrically opposite point, a positive electric varia- 

 tion indicative of enhanced turgor. It will thus be seen 

 that inhil)ition is possible even in the absence of contraction 

 of the upoer side of the tendril ; hence the contraction of 

 the directly stimulated side is neutralised by the effect of 

 indirect stimulation of the distal side. 



RESPONSE OF LESS EXCITABLE SIDE OP THE TENDRIL. 



It is generally supposed that the upper side of the 

 tendril of Passijlora is devoid of contractility. This is how- 

 ever not the case, for my experiments show that stimula- 

 tion of the upper side also induces contraction and con- 

 cavity of that side, though the actual movement is rela- 

 tively feeble. 



Experiment J09. — In order to subject the question to 

 quantitative test I applied feeble stimulus of the same 

 intensity on upper and lower side alternately. Successive 

 stimuli were kept more or less uniform by employing the 

 foUovsring device. I took a flat strip of wood 1 cm. in 

 breadth, and coated 2 cm. of its length with shellac varnish 

 mixed with fine emery powder. On drying the surface 

 became rough, the flat surface was gently pressed against 

 the area of the tendril to be stimulated, and quickly 

 drawn so that the rough surface 2 cm. x 1 cm. was rubbed 

 against the tendril in each experiment. Stimulation, thus 

 produced, induced a responsive movement of each side of 



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