404 



LIFE MOVEMENTS IN PLANTS 



the intensity of incident light. Thus in compass plants the 

 leaves, under moderate intensity of light in the morning 

 or in the evening, turn themselves so as to expose their 

 surfaces to the incident rays. But under intense sun light, 

 the leaves perform bendings and twistiugs so that they 

 stand at profile at midday. 



I have not yet been able to secure "Compass plants" 

 at Calcutta. I shall, however, describe my investigations on 

 the complicated torsional movemenis exhibited by certain 

 leaflets by the action of vertical light. The results 

 obtained from these will show that torsional movements, 

 even the most complex, are capable of explanation from 

 the general laws that have been established. 



Toi'siuiial movement of leaflet of Cassia alata : Experi- 

 ment 152. — These leaflets are closed laterally at night but 

 place themselves in an outspread position at day time. 

 The character of the movement is, however, modified by 

 the intensity of light. With moderate light in the morn- 

 ing the leaflets open out laterally. But under more intense 

 light, the pulvinules of the leaflets exhibit a torsion by 

 which the formerly infolded surfaces of the leaflets are 



Fig. 150. — Leaflets of Cassia alata : open in daytime, and closed in evening. 



exposed at right angles to light from above (Fig. 150)_ 

 Such complicated movements, in two directions of space, are 

 also exhibited by other leaflets which are closed at night 

 in a lateral direction. 



