vi CONTENTS 



CHAPTER VI 



THE INFLUENCE OF THE EXTERNAL CONDITIONS ON GROWTH 



PART I. GENERAL VIEW 



PAGE 



20. The Formal Conditions for Growth 68 



21. Formative Reactions . 71 



PART II. THE INFLUENCE OF TEMPERATURE 



22. The Cardinal Points for Growth 75 



PART III. THE INFLUENCE OF LIGHT 



23. General .............. 84 



24. Photomorphic Actions 85 



25. The Reaction of a Phototonic Plant to Changes of Illumination ... 94 



26. The Mode in which Light acts 98 



27. The Action of Rays of Different Wave-length 101 



PART IV. THE INFLUENCE OF MAGNETISM AND ELECTRICITY ON GROWTH 



28. ................ 106 



PART V. THE INFLUENCE OF GRAVITY AND OF CENTRIFUGAL FORCE ox GROWTH 



29. ................ 108 



PART VI. THE INFLUENCE OF CHEMICAL AGENCIES ON GROWTH 



30. General ill 



31. The Influence of Oxygen on Growth 114 



32. Changes of Form produced by Chemical Agencies 115 



PART VII. THE INFLUENCE OF THE PERCENTAGE OF WATER AND OF TURGIDITY 



33. The Action on Vegetative Growth 118 



34. The Influence on Form and Structure 120 



PART VIII. THE INFLUENCE OF MECHANICAL AGENCIES ON GROWTH 



35. Mechanical Actions 124 



36. The Stimulus of Tension 127 



37. Other Stimuli 129 



38. Traumatic Effects 133 



CHAPTER VII 



THE CAUSES OF SPECIFIC SHAPE 



39. General 136 



