xiv CONTENTS 



Page 



CHAPTER IX 



The Significance of Growth Substances for Geotropism . . . .169 



1 o y 



The early investigations 



The Avena coleoptile ■ • 



Stimulation and response— Distribution of geotropic sensitivity- 

 Transmission of the stimulus— The quantity-of-stimulus principle 

 —The course of geotropic curvature— The growth-substance 

 explanation— Growth substance and geotropic sensitivity— The 

 unequal distribution of growth substance— The statolith theory- 

 Electrical theories and experiments— Comparison of phototropic 

 and geotropic curvatures— Recovery from geotropic curvature 

 brings about equilibrium. 



Dicotyledonous hvpocotyls, shoots, etc 



Stimulation and response— Distribution of geotropic sensitivity— 

 Negatively geotropic curvature in stems— The growth-substance 

 explanation— Experiments with split stems— Growth-substance 

 displacement— Electrical transport of growth substance— Inherit- 

 ance of geotropic response— Geotropic response in nodes. 



Roots .■ ■ ... ., 



Stimulation and response— Distribution of geotropic sensitivity- 

 Stimulus transmission— The quantity-of-stimulus principle- 

 Growth in geotropic curvature— The growth-substance explanation 

 of root curvature— Similarity of growth substance in the root and 

 coleoptile— Extraction of growth substance from roots— Transverse 

 distribution of growth substance— Mechanism of growth-substance 

 displacement. 

 Summary 



CHAPTER X 

 The Significance of Growth Substances for Traumatic and 



Thigmatic Curvatures ,• ' u ' 



General survev of the phenomena— Amputations— Wounding by 

 incisions— Chemical treatment— Stimulus transmission— Trans- 

 mission in the Avena coleoptile— Transmission in roots— Transmis- 

 sion in Mimosa— The growth-substance explanation— Amputa- 

 tions— Wounding by incisions. ' ^^^ 

 Summary 



221 

 Bibliography 



247 

 Supplementary Bibliography s 



255 



Index 



