twIniNg Of tendrils '29^ 



Experiment 110. — A tendril of Passijiora was held in 

 a clamp, as in the diat^ram (Fig. 1U6) in which the left 

 is the more excitable side of the or^ran. The responsive 

 movement of the tendril is o])served by focussing a read- 

 ing microscope on a mark on the upper part of the 

 tendril. Direct mechanical stimulation at the dotted 

 arrow makes the tendril move in the same direction, the 

 response being positive. But if stimulus be applied on 

 the same side below the clamp the tendril is found to 

 move away from stimulus, the response being now 

 iiefjative. This reversal of response, as previously stated, 

 is due to the fact that the transmitted effect of indirect 

 stimulus induces an acceleration of growth higher up on the 

 same side, which now becomes convex. The result though 

 unexpected, is in every way parallel to the response of the 

 flower bud of Crinam, in which the normal positive res- 

 ponse was converted into negative by changing the point 

 of application of stimulus, so that it became indirect (p. 

 216). 



SUMMARY, 



The response of tendril is in no way different from 

 that of growing organs in general. 



Direct stimulus, electrical or mechanical, induces an inci- 

 pient contraction ; the after-effect of a feeble stimulus is an 

 acceleration of growth above the normal. Indirect stimulus 

 induces an enhancement of the rate of growth. 



Under unilateral mechanical stimulus of short duration 

 the directly excited proximal side undergoes contraction, 

 the indirectly stimulated distal side exhibits the opposite 

 effect of expansion. The induced curvature is thus due 

 to the joint effects of the contraction of one side, and the 

 expansion of the opposite side. 



