370 LIFE MOVEMENTS IN PLANTS 



excitation is not neutralised by transverse conduction (see 

 below). 



RESPONSE TO UNILATERAL STIMULUS IN THE GROWING 



REGION. 



Experiment 138. — The growing region of the hypocotyl 

 of Setaria is supposed to be totally devoid of the power 

 of perception. In order to subject the question to experi- 

 mental test, I applied unilateral light on the growing 

 region of the same specimen, after it had recovered from 

 the effect of previous stimulation. The response now ob- 

 tained was vigorous and was ab-initio positive. Direct 

 stimulus has thus induced the normal effect of contraction 

 and concavity of the excited side. The belief that the 

 hypocotyl of Setaria is incapable of perceiving stimulus 

 is thus without any foundation. The further experiment 



Fig. 137. — Effect of application of light to the growing hypocotyl at arrow 

 induced positive pbototropic curvature followed by neutralisation. Application 

 of indirect stimulus at dotted arrow on the tip gave rise at first to negative, 

 subsequently to positive curvature. (Seedling of Setaria). 



which I shall presently describe will, however, offer an 

 explanation of the prevailing error. On continuing the 



