582 



LIFE MOVEMENTS IN PLANTS 



Experiment 221. — I obtained 24 hours' record of varia- 

 tion of torsional response of Mimosa, commencing with 

 thermal-noon at 2 p.m. It is to be borne in mind that 

 increase of torsion indicates increase of geotropic action, 

 just as the erectile movement of the leaf in the normal 

 position indicates the enhanced geotropic effect. Inspection 

 of figure 211 shows that the fall of temperature after 

 thermal-noon was attended by increase of torsion. The 



Fig. 211. — Record of diurnal variation of torsion in Mimosa leaf. Up-curve 

 represents increase and down-curve decrease of geotropic torsion. 



curve went up till about 5 p.m., as in the ordinary 

 record of Mimosa. The torsion suddenly decreased with the 

 rapid diminution of light after 5 p.m. The torsion then 

 increased with falling temperature from 9 p.m. till 

 thermal-dawn next morning. After 6 a.m. there is a 

 continuous diminution of torsion till 5 p.m. 



We may now summarise the diurnal variation of 

 torsion exhibited by Mimosa. The torsion undergoes a 



