TRANSMITTED EFFECT OF LIGHT 



373 



Experiment 139. — I have explained, (Expt. 126) that unila- 

 teral application of stimulus of light on the upper half of 

 the responding pulvinus of Mimosa induces an up or positive 

 curvature, followed by a neutralisation and even a reversal 

 into negative, the last two effects being brought about 

 by transverse conduction of excitation to the distal side. 

 When the incident light is of moderate intensity, the trans- 

 mitted excitation only sutiices to induce neutralisation 



Fig. 138. — (a) Diagrammatic representation of direct application of light (|) 

 on the pulvinus and the indirect application on the stem (— ■^) (b) Record of 

 eflfect of direct stimulus, positive curvature followed by neutralisation. Super- 

 position of the positive reaction of indirect stimulus induces erectile up-response 

 followed by down movement due to transmitted e.^citatory impulse (Mimosa). 



without further reversal into negative ; while in this state 

 of balanced neutralisation let us apply indirect stimulus 

 by throwing light on the stem at a point directly opposite 

 to the leaf (Fig. 138). 



Two different impulses are thus initiated from the effect 

 of indirect stimulus. In the present case the positive 



