544 LIFE MOVEMENTS IN PLANTS 



whereas the leaflets of Averrhoa caiamhola a folding 

 downwards. The explanation of the difference lies in 

 the fact that in the leaflets of Mimosa it is the upper 

 half, and in Avei'rhoa it is the lower half of the 

 pulviuule, that is the more excitable. This difference may 

 be demonstrated by the action of diffuse electric shock 

 under which the leaflets of Mimosa exhibit an upward, 

 and those of Averrhoa a downward, closure. I have 

 also shown that conduction of excitation takes place across 

 the pulvinule ; hence the strong excitation caused by sun- 

 light becomes internally diffused, and brings about the 

 responsive movements, the direction of which is deter- 

 mined by the mora excitable half of the pulvinule. 



SUMMARY. 



Rise of temperature induces a movement of closure of 

 the leaflet of Cassia, fall of temperature inducing the 

 opposite movement. 



Artificial darkness induces a closure of the leaflets, the 

 closure being completed in the course of an hour. On 

 readmission of light, the leaflets become fully expanded 

 in the course of one hour and a quarter. The leaflets 

 are extremely sensitive to light, closure movement being 

 induced by the transitory passage of a cloud. 



The efl'ect of rise of temperature is antagonistic to the 

 action of light. The movement of opening during the course 

 of the day is due to the effect of light overpowering the 

 effect of rise of temperature. 



Under daily variation of light and darkness, the 

 movement of closure is initiated at about 5 p.m., when 

 the light is undergoing a rapid diminution. The movement 

 of closure is complete by 9 p.m. The leaflets remain closed 

 till about 5 a.m. next morning, after which they begin to 

 open and become fully expanded by 9 a.m. 



