514 



LIFE MOVEMENTS IN PLANTS 



door of the plant chamber gradually opened, so as to aMow 

 the temperature to be restored to the normal. Cooled air 

 was next introduced into the chamber till the temperature 



fell to 26 C. Figure. 1«6 

 exhibits clearly the effect 

 of variation of tempera- 

 ture on geotropic torsion. 

 The maximum torsion had 

 been attained at 30°C. 

 and the first part of the 

 record is therefore hori- 

 zontal. Warmth was ap- 

 plied at H, and after a 

 latent period of ten 

 minutes, the geotropic 

 torsion underwent a con- 

 tinuous diminution till a 

 new state of equilibrium 

 was reached at 84°C. This 

 took place shortly after 

 the stoppage of the heat- 

 ing current at (H). On return to normal temperature the 

 torsional balance was restored to its original position of 

 equilibrium. Application of cold at C, is seen to bring 

 about a new state of balance with an increase of geotropic 

 torsion. 



The position of geotropic equilibrium is thus seen to be 

 modified by variation of temperature, the tropic eflect 

 being diminished with the rise, and enhanced with the fall 

 of temperature. 



It may be thought that the phenomenon just descril)ed 

 nay not be different from ordinary thermonasty, exhi- 

 l)ited by the perianth leaves of Crocus and Tulip in which 

 a rise of temperature induces a movement of unfolding, 

 and a fall of temperature brings about the opposite move- 



FlCi. 18G. — Effect of variation of tempera- 

 ture on geotropic torsion. Application of 

 warmth at H diminishes the geotropic tor- 

 sion : return to normal temperature (H) 

 restores the original torsion : cooling at C, 

 increases the geotropic torsion. 



