CHAPTER LI 



RESPONSIVE GROWTH-CURVATURES IN PLANTS 



Longitudinal growth and its variations — Effect of temperature on growth — Re- 

 sponsive growth-curvature under unilateral stimulation :— I. Direct unilateral 

 stimulus on the responding organ : (a) Positive response under moderate stimu- 

 lation ; (/') Intermediate or neutral response ; (r) Negative response ; {d) Dorsi- 

 ventral positive response ; («) Dorsi-ventral response which may become 

 negative— 2. Indirect effect of unilateral stimulation : .(a) Negative response ; 

 (b) Positive response — Responsive action under stimulus of gravity — Helio- 

 tropic action in radial organs — Heliotropic action in plagiotropic and dorsi- 

 ventral organs — Phototactic movements — Nyctitropic movements. 



We shall next pass in review the responsive growth- 

 curvatures induced in plants by various agencies, and shall 

 then in the following chapter consider at some length the 

 extended range of those similarities which exist as between 

 the physiological responses of plant and of animal tissues. 



Longitudinal growth and its variations.— It was shown 

 by means of the highly magnified continuous record which 

 was obtained with the ordinary and Balanced Crescographs, 

 that growth was a phenomenon of multiple response ; and 

 it was further shown that these multiple responses of growth 

 exhibited the same characteristics as had previously been 

 observed in the multiple motile responses of Biophytum and 

 Desmodium. Each of the constituent responses consisted of 

 a sudden elongation due to a pulse of increased turgidity, 

 followed by an incomplete recovery. The irreversible 

 growth-effect consisted of the difference between this elon- 

 gation and its recovery. These pulses of positive turgidity- 

 variation were mainly due to excitatory reactions occurring 

 about the zone of growth, which delivered from within, upon 



