CONTENTS iii 



XXIX.— ON PHOTOTROPISM. 



PAGE. 



Complexity of piohleni of phototropic reaction — Action of 

 liglit — Positive phototropic curvature of pulvinated 

 organs — Positive phototropic curvature of growing 

 organs — Plienoineuon of recovery — Immediate and after- 

 ortect of light on growtli — Latent period of phototropic 

 reaction — Growtli variation induced by flash of light 

 from a single spark — Maximum positive curvature under 

 continued action of light ...... 31.3 



XXX.— DlA-PHOTOTROPISM AND NEGATIVE PHOTOTROPISM. 



Differential excitability of two i;alves of pulvinus of Mimosa 

 — Transformation of positive to negative curvature — 

 Tropic effect under sunlight — Negative phototropism of 

 slioot and root ........ 328 



XXXI.— REL'ATION BETWEEN THE QUANTITY OF LIGHT AND 

 THE INDUCED PHOTOTROPIC CURVATURE. 



Effect of increasing intensity of light on pulvinated and 

 growing organs — Effect of increasing angle — Effect of 

 duration of exposure ....... 338 



XXXII.— THE PHOTOTROPIC CURVE AND ITS CHARAC- 

 TERISTICS. 



Summation of stimulus — General consideration — The general 

 characteristic curve — Characteristics of simple phototropic 

 curve — Variation of susceptibility for excitation in 

 different parth of the curve — Effect of sub-minimal 

 stimulus — The complete phototropic curves of pulvinated 

 and QTOwing organs — Limitation of Weljor's law . 346 



f] 



