SUMMARY 419 



The results of the above experiments prove that the 

 effect of light is algebraically summated with that of auto- 

 nomous torsion, and also with that induced by geotropic 

 stimulation. 



Summary 



It has been shown that the twining of stems is brought 

 about by circumnutation, which is the expression of auto- 

 nomous torsion. 



The stem being also sensitive to the stimulus of contact, 

 twining takes place when the circumnutating stem comes 

 into contact with a support. 



The twisting stem is alike sensitive to all modes of 

 stimulation, electric, thermal, photic, and geotropic. 



All forms of diffuse stimulation have a retarding effect 

 on growth. 



The twisting stem is an anisotropic organ, the two 

 diverse longitudinal halves of which are unequally excitable. 

 Diffuse stimulation induces greater retardation of growth 

 in the more active half, which reduces the normal rate of 

 torsion even to reversal of direction. 



Under lateral stimulation by light or gravity, a tor- 

 sional response is evoked in all anisotropic organs. When 

 the stimulus acts on the A flank, a maximum anti-clock- 

 wise movement is induced. The effect of stimulation of 

 the diametrically opposite flank R is a clockwise move- 

 ment. No responsive torsion occurs on stimulation of the 

 neutral sides N, N'. 



The responsive reactions, algebraically summated with 

 the autonomous torsion, explain the varied movements of 

 twisting organs under the simultaneous action of different 

 stimuli. 



The reactions to light and gravity are algebraically 

 summated with the autonomous torsion. Light, when 

 sufficiently strong, acting in opposition to gravitational 

 stimulus, induces a reversal of the direction of torsion. 



