1 68 CHAP. XV. PHOTONASTIC PHENOMENA 



Experiment loo. Application of strong light from above. — 

 The response was a brief erectile movement, due to the 

 contraction of the directly stimulated upper side of the 



Fig. 95. Response of leaflet of Averrhoa to strong light from 



above. 



organ ; it was positively phototropic, i.e, movement towards 

 the source of illumination. The response was subsequently 

 reversed to strong negative in consequence of transverse 

 conduction of excitation (fig. 95). 



Fig. 96. Effect of strong light applied below (Averrhoa). 



Experiment loi. Application of strong light from below. — 

 The response was positively phototropic, that is, towards the 

 source of illumination. As the more excitable lower side 

 was directly stimulated, its predominant contraction was 

 incapable of being neutralised by excitation transversely 

 transmitted to the less excitable upper side (fig. 96). 



