X TABLE OF CONTENTS 



CHAPTER PAGE 



VI. AUXIN TRANSPORT AND POLARITY 90 



A. Auxin Transport in General 90 



B. Polarity in General 91 



C. Polarity of Auxin Transport 93 



D. Other Views on the Transport of Auxin 98 



E. Possible Mechanisms of Auxin Transport 101 



VII. THE CHEMISTRY OF THE AUXINS 105 



A. Early Work 105 



B. The Isolation of Auxins a and 6 106 



C. Discovery of Indole-3-Acetic Acid as an Auxin . . . 110 



D. Identity of the Native Plant Growth Hormone . . . 113 



E. Activity of Compounds Related to Indole-Acetic Acid 114 



VIIL THE MECHANISM OF THE ACTION 118 



I. The Physiological Approach 119 



A. Definitions 119 



B. Nature of Growth 119 



C. Effect of Auxin on the Cell Wall ...... 121 



D. Structure of the Growing Cell Wall 124 



E. The Intermediate Processes 127 



F. The Effect of Acid on Growth 130 



11. The Chemical Approach 132 



G. Primary and Secondary Activity 132 



H. The Relation between Structure and Activity . . . 136 



IX. THE GROWTH OF ROOTS 141 



A. The Effect of the Tip in Root Growth 141 



B. The Effect of Auxin on Root Growth 142 



C. Auxin Production in the Root 144 



D. The Role of Auxin in the Growth of Roots .... 148 



X. TROPISMS 151 



I. Tropisms in General 151 



A. Historical Introduction 152 



B. The Cholodny-Went Theory 154 



II. Geotropism 157 



C. Geotropism of Shoots 157 



D. Geotropism of Roots 161 



E. The Mechanism of Geotropic Perception .... 164 

 HI. Phototropism 166 



F. Auxin Redistribution 166 



G. Light-Growth Reactions 171 



H. Comparison of Phototropic and Geotropic Curvatures . 176 



rV. Other Tropistic Responses 178 



J. Traumatotropism 178 



K. Electrotropism 179 



L. Chemotropism 181 



M. Nastic Movements 181 



