252 



CHAP. XXIII. PHOTOTROPIC TORSION 



against the hands of a clock. This responsive torsion, right- 

 handed or left-handed, will presently be shown to depend on 

 the direction of the incident stimulus. 



Fig. 144. Diagrammatic representation of the Torsional 



Recorder. 



Lateral stimulation, r, applied on right flank (dotted arrow) induces 

 clockwise torsion c (dotted circle). Stimulus, l, applied on 

 left flank (full arrow) induces anti-clockwise torsion a (thick 

 circle). 



Effect of Lateral Stimulation by Light 



Experiment 135. — The pulvinus of the leaf was stimu- 

 lated by a horizontal beam of light thrown laterally upon 

 it ; the area contiguous to the line of junction of the 

 upper and lower halves of the anisotropic organ responded 

 by differential contraction. When light struck on the 



