ABSORPTION AND EMISSION OF ENERGY IN RESPONSE 79 



absorbed stimulus induced a positive turgidity-variation, with 

 enhanced rate of growth, as seen by the up-curve. But by 

 this absorption of the stimulus itself, the tonic condition 

 of the specimen was raised, with consequent increase of ex- 

 citability, and the response became normal. That is to say, 

 it now consisted of contraction and retardation of growth 

 as seen by the downward curve. The external stimulus was 

 now cut off and the 

 dotted portion of the 

 curve shows the after- 

 effect. The after-effect 

 is thus not a mere re- 

 covery, but an enhanced 

 rate of growth, due to the 

 increased energy which 

 remains latent. It was 

 only when this was ex- 

 hausted that the normal 

 rate of growth was re- 

 established, as seen in 

 the horizontal part of the Continuous lines represent the effect during 



application of light, the dotted line on 



FIG. 52. Balanced Record of Variation of 

 Growth in Flower-bud of Crinum Lily 

 under Diffuse Stimulation of Light 



curve. And as the tissue 

 was now in full tonic 

 condition the renewed 

 application of stimulus 

 of light did not again 

 induce a preliminary en- 

 hancement of the rate of 

 growth, but the normal 



withdrawal of light. The plant was 

 originally in a sub-tonic condition, and 

 application of light at x , after short 

 latent period, induces preliminary ac- 

 celeration of growth. After this follows 

 the normal retardation. On withdrawal 

 of light, in the dotted portion of the curve 

 is seen the after-effect, followed by 

 return to the normal rate of growth, 

 A second and long-continued application 

 of light induces retardation, followed by 

 oscillatory response. 



contraction and retarda- 

 tion. Its long-continued application gave rise to the further 

 phenomenon of multiple response, a subject which will be 

 fully dealt with in a future chapter. 



Now owing to this fact that the response of growth gives 

 us by means of the enhancement or depression of its rate, 

 effects which correspond to the positive and negative, we are 

 able clearly to perceive : 



