396 LIFE MOVEMENTS IN PLANTS 



The change of phototropic curvature exhibited by 

 Tropceolum majus and Ivy, from positive in autumn to 

 negative in summer, is probably due to the effect of tem- 

 perature. Higher temperature with enhanced transverse 

 conductivity in summer, may thus convert positive into 

 negative curvature. 



The physiological effects of vise of temperature and the 

 stimulus of light are antagonistic to each other. 



Rise of temperature tends to neutralise or reverse the 

 positive phototropic curvature. The after-effect of temperature 

 is often very persistent. 



