414 ch. xxxvi. torsion under unilateral stimulation 



Effect of Unilateral Stimulation by Gravity 



As the direction of stimulus of gravity is fixed, the differ- 

 ent sides of the twisting stem can only be exposed to it by 



Fig. 226. Optical Method of observing rate of torsional move- 

 ment under unilateral stimulation by gravity. The different 

 sides of the horizontally laid stem are exposed to vertical 

 lines of force of gravity by rotating the plant-holder with 

 attached index, the angle being measured by the circular 

 scale. 



rotating the horizontally laid stem round its axis. The 

 diagrammatic representation of the apparatus explains 

 the method of observing the rate of torsional movement. 

 The different sides of the organ are subjected to the stimulus 

 of gravity G, by rotating the small cylindrical vessel of 



