INDIRECT UNILATERAL STIMULATION 



95 



Effect of Indirect Unilateral Mechanical 



Stimulation 



Experiment 56. — A tendril of Passiflora was held in a 

 clamp as in the diagram, (fig. 48) . The responsive movement 

 of the tendril was observed by focusing a reading-micro- 

 scope on a mark on the upper part 

 of the tendril. Direct mechanical 

 stimulation made the tendril move 

 towards the stimulated side, the 

 response being positive, as was also 

 found in the last experiment. The 

 stimulus was next transferred to a 

 point below the clamp, but on the 

 same side as before. This gave rise to 

 a negative responsive movem.ent, i.e. 

 in a direction away from the stimulated 

 side. This reversal into negative tropic 

 curvature is due to the fact that the 

 transmitted effect of indirect stimula- 

 tion induces an acceleration of growth 

 on the same side higher up, producing 

 a convexity in the growing region. 



The different effects of direct and 

 indirect unilateral stimulation are 

 clearly in dicated in the diagram (fig. 48) . 



Fig. 48. Diagrammatic 

 representation of effect 

 of indirect and direct 

 unilateral stimulation 

 of a tendril (Passiflora) . 



Indirect stimulation i in- 

 duces movement away 

 from stimulated side 

 (negative curvature), 

 represented by con- 

 tinuous arrow above. 

 Direct stimulation d 

 induces positive curva- 

 ture, indicated by 

 dotted arrow above. 



Electric Response of Proximal 

 AND Distal Sides 



The effects of unilateral stimulation 

 on the two sides of the organ were 

 next determined by the test of elec- 

 tric response, in which excitatory reaction is detected by 

 electric change of galvanometric negativity, while expansive 

 reaction is indicated by galvanometric positivity. 



Experiment 57.— Taking a tendril, I made suitable 

 electric connections for two series of experiments with an 

 identical specimen. In the first, an electric connection 



