574 



PLANT RESPONSE 



of retarding growth. In order to verify this inference I took a 

 growing flower-bud of Crinum Lily, which had been previously 

 kept in the dark. And for the further purpose of detecting 

 even the transitory variations, I used the delicate method of 

 balanced record. On now subjecting the specimen to the 

 stimulation of sunlight, acting on it from all sides, I observed 

 a preliminary acceleration of growth, which lasted one 



minute (fig. 235). By 

 this time the plant had 

 evidently attained its nor- 

 mal tonic condition, and 

 the continued action of 

 light resulted in a retarda- 

 tion of growth, as seen in 

 the rapid descent of the 

 curve. The light was 

 next shut off, and the 

 after-effect of absorbed 

 energy is seen in the con- 

 sequent acceleration of 

 the rate of growth above 

 the normal. This ac- 

 celeration lasted for four 

 minutes, after which the 

 plant returned to almost 

 its normal growth, as seen 

 by the record approximat- 

 ing to the horizontal. The 

 plant may at this point 

 be regarded as in ordinary 

 tonic condition. Light was again applied, and retardation of 

 growth is immediately shown by the descent of the curve. 

 There is now no preliminary acceleration of growth, as in the 

 case when the plant was sub-tonic. Under the long-continued 

 action of light, there is now seen the very interesting 

 phenomenon of the induction of autonomous pulsations of 

 the rate of growth, whose period is about ten minutes. 



Fig. 235. Balanced Record of Variation 

 of Growth in Flower-bud of Crinum 

 Lily under Diffuse Stimulation of Light 



Continuous lines represent the effect during 

 application of light, the dotted line on 

 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 negative 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. 



