274 CHAP. XXV. DIURNAL MOVEMENT OF MIMOSA 



mind that increase of torsion corresponds with the erectile 

 movement of the leaf in the diurnal thermo-geotropic 

 curve. Inspection of fig. 159 shows that the fall of tempera- 

 ture after thermal noon at 2 p.m. was attended by an increase 

 of torsion. The curve went up till about 5 p.m., as in the 

 ordinary record of Mimosa. The torsion suddenly decreased 

 under rapid diminution of hght after 5 p.m. The torsion 



Fig. 159. Record of diurnal variation of geotropic torsion in 



Mimosa leaf. 



Up-curve represents increase, and down-curve decrease of torsion. 



then increased with falling temperature from 9 p.m. till 

 thermal dawn next morning. After 6 a.m. there was a 

 continuous diminution of torsion till 2 p.m. 



The diurnal variation of geotropic torsion exhibited by 

 Mimosa may be summarised as follows : The torsion undergoes 

 periodic increase during the fall of temperature from after- 

 noon till next morning, and diminution during rising tem- 

 perature from morning till afternoon. A sudden diminution 

 of torsion occurs at about 5 p.m., due to the disappearance 

 of light. The torsional record is, to all intents and purposes. 



