CONTENTS XIX 



PAGE 



stimulation by thermal radiation — EfEect of differential excita- 

 bility on the direction of torsion — Laws of Torsional Response- 

 Advantages of Method of Torsional Response — The Torsional 

 Balance .....••••• 250 



CHAPTER XXIV 



THE AFTER-EFFECT OF LIGHT 



Immediate and aftereffect of light— Determination of aftereffect 

 by electric response — Characteristic after-effects at pre-maximum, 

 at maximum, and at post maximum — Modification of after-effect 

 by duration of incident stimulation — Iropic response to hght and 

 its aftereffect — Aftereffect at pre maximum — Aftereffect at 

 maximum — Post maximum after effect in Cassia . . .259 



CHAPTER XXV 



THE DIURNAL MOVEMENT OF THE LEAF OF MIMOSA 



Diurnal record of :Mimosa exhibiting four phases of reaction — Com- 

 plexity attributable to algebraical summation of several effects : 

 (i) of thermo geotropic reaction, (2) of immediate effect of photic 

 stimulus, and (3) of after-effect of hght — Autonomous pulsation of 

 the leaf— Spasmodic fall of the leaf in the evening— Diurnal move- 

 ment of petiole after removal of sub-petioles — Diurnal variation 

 of geotropic torsion of the pulvinus — Characteristic after-effects 

 of light on Mimosa — Abrupt fall of leaf in the evening is a post- 

 maximum after-effect of photic stimulation — Diurnal curve of 

 petiole of Cassia ....••••• ~^1 



CHAPTER XXVI 



GEOTROPISM 



Apparent difference in sign of response of shoot and root under 

 geotropic stimulation— Uncertainty of fundamental reaction, 

 whether contraction or expansion— Direction of geotropic 

 stimulus — The Geotropic Recorder — Determination of the true 

 character of geotropic reaction by electrical method— Deter- 

 mination of the latent period— The complete geotropic curve- 

 Determination of direction of geotropic stimulus— Algebraical 

 summation of effects of light and gravity— Analogy between 

 phototropic and geotropic reactions— Relation between directive 

 angle and geotropic reaction— Differential geotropic excitation . 281 



