51f) LIFE M0VBMENTt4 IN PLANTS 



is laid on its left side in the a-position, the risrht flank 

 will be above and the responsive torsion under geotropic 

 stimulus becomes right handed or with the hands of a 

 clock (Cf. Fig. 179). When the plant is laid on its right side, 

 the left flank will be above and the geotropic torsion 

 becomes left handed or against the hands of the clock. 



It Avill be seen from the above that in whatever way 

 the experimental condition may be varied, the movement 

 in response to variation of temperature is determined in 

 relation to the antecedent geotropic torsion. The geotropic 

 effect whether left-handed or right-handed torsion is always 

 diminished by the rise of temperature, and enhanced by 

 the fall of temperature. 



VARIATION OF APO-GEOTROPIC CURVATURE UNDER 

 4 THERMAL CHANGE. 



I shall now proceed to show that variation of temper- 

 ature not merely induces variation of geotropic torsion but 

 also of geotropic curvature. I shall first demonstrate the 

 effect of thermal change on geotropic curvature of the 

 shoot, and then demonstrate its effect on dia-geotropic cur- 

 vature of leaves. 



Experiment 200. — A specimen of 'rntpwiUmi niajns 

 grown in a small flower pot, is laid on its side. Under 

 geotropic action the shoot becomes curved, the upper side 

 becoming concave and the lower side convex. The end of 

 the stem is attached to the recording apparatus ; when 

 the plant is subjected to a rise of temperature, the move- 

 ment induced shows that the geotropic effect has undergone 

 a diminution, the curvature exhibiting a flattening; lowering 

 of temperature, on the other hand, increases tlu geotropic 

 curvature. Other instances of this will be found in a subse- 

 quent chapter. The diurnal movement of the ' Praying 

 Palm ' is a striking example of the effect of variation of 

 emperature in modification of geotropic curvature (p. oO)- 



I 



