AUTONOMOUS TORSION 669 



but this was shown not to be due to any actual arrest 

 brought about by heat-rigor, for the rhythmic activity 

 induced at this high temperature was even greater than 

 before (p. 432). Now, in the case of torsional response, I find 

 that though the rate of torsion undergoes a continuous 

 decrease up to 42 C. or 43 C, yet beyond this an unex- 

 pected increase is induced. Thus in the experiment just 

 described, the torsional movement at 45 C. was at least 

 temporarily enhanced to '8° per minute. This phenomenon 

 may be due to abnormal relaxation at these high temperatures. 

 Or there is another possible explanation. It has been said 

 that the resultant torsion is due to the differential growth- 

 activities of two antagonistic elements. Now, it may be that 

 at 44 C. or thereabouts the growth of the less excitable of 

 these antagonistic elements may undergo the same kind of 

 arrest as we have seen to occur in the longitudinal growth of 

 a radial organ. The sudden increase observed at and above 

 44 C. in the rate of natural torsion may then be due to the 

 withdrawal of the resistance previously offered by the growth- 

 activity of the antagonistic element. 



Effect of increased suctional activity. — Another in- 

 teresting point, in connection with the occurrence of auto- 

 nomous torsion, lies in the fact that its rate is enhanced by 

 any means which tends to increase internal energy. One 

 example of this has just been seen in the effect induced by 

 rise of temperature. Another is found in the application of 

 warm water to the base of the specimen, a process which has 

 already been shown, in the case of radial organs, to cause, by 

 means of the consequent increase of suctional activity, a 

 sudden enhancement of the rate of autonomous growth 

 (p. 430). I find, similarly, that the application of warm 

 water to its base enhances the torsional response of a torsion- 

 ing plant. 



Effect on natural torsion of unilateral application of 

 light. — We have seen that when an anisotropic organ is 

 laterally excited by external stimulus, a response torsion 

 takes place, by which the less excitable side is made to face 



