leaflet of mimosa 169 



Response of the Leaflet of Mlmosa 



Diffuse stimulation causes upward closure of the leaflet, 

 proving that the excitability of the pulvinule is greater 

 on the upper side. 



Experiment 102. Effect of strong light on upper side. — 

 The result is a very pronounced up-response, due to direct 

 stimulation of the more excitable side, which was not re- 

 versed by transverse conduction of excitation to the lower 

 less excitable side of the pulvinule (fig. 97). 



Fig. 97. Fig. 98. 



Fig. 97. Effect of strong light on upper side of Mimosa leaflet. 

 Fig. 98. Effect of strong light on lower side of leaflet. 



Experiment 103. Effect of strong light on lower side. — ■ 

 A transitory down-response occurred, due to contraction of 

 the directly stimulated lower side ; this was subsequently 

 reversed into a strong up-response by transverse conduction 

 of excitation to the more excitable upper side (fig. 98). 



These responsive manifestations find their fullest ex- 

 planation in the previous experiments on the main pulvinus 

 of Mimosa under the action of strong light, acting from 

 above or below. Had a delicate means of record not been 

 available, the gradual transition from positive to nega- 

 tive phototropic curvature would have passed unnoticed. 



