PHOTONASTIC CURVATURES 



383 



heliotropic when acted from below, is now fully removed. 

 The response of the leaflets is also seen to be determined 

 by the directive action of light, though the short-lived 

 response of the less excitable lower side is quickly masked 

 by the predominant reaction of the more excitable upper 

 aide of the organ. 



Fig. 142. Fig. 143. 



Fig. 142.— Response of leaflet of Mimosa to light applied below : transient 

 positive followed by pronounced negative curvature. 



Fig. 143. — Response of leaflet of Averrhoa, to light applied above: transient 

 positive followed by pronounced negative curvature. 



Up-curve represents up-movement, and down-curve, down-movement. 



NEGATIVE PARA-HELIOTROPISM. 



Response of leaflet of Averrhoa carambola : Experiment 

 144. — The leaflets of this plant, and also those of Biophytum 

 sensitivum fold downwards under action of strong light, 

 applied above or below. In these leaflets difl'use electric 

 stimulation induce a fall of the leaflets demonstrating the 

 greater excitability of the lower half of the pulvinule. The 

 analysis of reaction under light is rendered possible from 



