28o CHAP. XXV. DIURNAL MOVEMENT OE MiMOSA 



Summary 



The very complex type of diurnal movement of the 

 J^rimary petiole of Mimosa results from the combined effects 

 of thermo-geotropism and phototropism. 



With the exception of a small part of the curve in the 

 •evening, the diurnal curve of the leaf is essentially similar 

 to the typical thermo-geotropic curve, exhibiting an erectile 

 movement from thermal noon to thermal dawn, and a fall 

 from thermal dawn to thermal noon. 



The torsional response of the leaf of Mimosa exhibits 

 a diurnal variation similar to that exhibited when the leaf 

 is in the normal position. 



The leaf of Cassia alata exhibits a diurnal movement 

 of the same type as that of Mimosa. 



The spasmodic fall of the leaf of Mimosa towards 

 evening is not due to the increased mechanical moment 

 caused by the forward position of the sub-petioles. The 

 record of the leaf with amputated sub-petioles exhibits 

 the same sudden fall in the evening as does that of the 

 intact leaf. 



The evening fall of the leaf is shown to be a post- 

 maximum after-effect of light, which causes an over- 

 shooting, the fall of the leaf carrying it below the position 

 of equilibrium. 



