THERMO-GEOTROPISM 519 



of the plant chamber, and warm water was made to circulate 

 through them ; this device ensured a steady rise of tem- 

 perature. The flow of warm water was then stopped and 

 the plant chamber was allowed to cool down ; the fall of 

 temperature was at first moderately rapid, but later on the 

 rate of cooling became extremely slow ; on account of 

 this the temperature of the plant chamber, towards 

 the end of the experiment remained higher than the 

 normal temperature outside. The rate of rise and fall of 

 temperature during the entire course is illustrated in the 

 thernio-graphic (a) tracing (Fig. 187); the record (6) exhibits 

 the movement of the leaf in a vertical plane, rise of tem- 

 perature being attended by a diminution of geotropic curva- 

 ture resulting in the fall of the leaf, the fall of tempera- 

 ture inducing the opposite effect. In record (c) is seen 

 the responsive variation of geotropic torsion, rise of 

 temperature inducing a diminution and fall of tempe- 

 rature causing an enhancement of torsion. The results 

 obtained by diverse methods thus prove that the geotropic 

 effect is diminished under rise, and increased under fall of 

 temperature. 



SUMMARY. 



The position of equilibrium under geotropic action is 

 not fixed but undergoes change with variation of temper- 

 ature. 



The geotropic curvature and torsion are increased by 

 lowering of temperature, and decreased by rise of temper- 

 ature. This is equally true of apo-geotropic and 

 dia-geotropic curvatures, 



38 



