xii CONTENTS I 



Page ] 



CHAPTER III ! 



Preparation and Properties of Growth Substances 40 j 



Preparation from plant and animal sources 40 ' 



Rhizopus, a source of growth substance — The identity of "rhizo- i 



pin" and 3-indole acetic acid — Aspergillus, a source of growth sub- 

 stance — Substratum content and growth substance production 

 — Urine, a source of auxentriolic acid (auxin a) — Maize oil, malt 

 and other sources of auxenolonic acid (auxin 5)— Urine, a source of 

 3-indole acetic acid (heteroauxin) — Yeast, a source of heteroauxin. 



Properties of growth substances 50 



The structural constitution of the auxins— Physical and chemical ^ 



characteristics of the auxins crystallized from plant materials — 

 Physiological effectiveness of the auxins, their derivatives, and ; 



other compounds. 

 Summary 55 



CHAPTER IV 

 The Occurrence and Formation of Growth Substances 56 



Occurrence 56 j 



Higher plants — Growth substance in coleoptiles — Foliage leaves — 



Growth substance in hypocotyls, shoots and flower stalks — Roots 



—Pollen — Fruits and seeds— Lower plants — Plant products — i 



Human and animal organisms. 



The formation of growth substances 64 



Lower plants — Higher plants — Production of auxin in human | 



urine. i 



Summary 69 



CHAPTER V 



The Transport of Growth Substances 71 I 



The Avena coleoptile — The conducting tissue — Polarity of trans- 

 port — Rate and amount of transport — Rate of transport — 

 Amount of transport — X-irradiation and transport — Anaesthesia 

 and transport — Growth-substance transport in shoots and roots — 

 The mechanism of growth-substance transport — Diffusion — Proto- , 



plasmic streaming — Surface tension — Electrophoresis — Movement I 



of growth substance from agar blocks into decapitated Avena j 



coleoptiles. 

 Summary 79 



CHAPTER VI 



The Significance of Growth Substances for the Normal Growth 



OF Plants 81 



General survey of the effect of growth substances upon growth. . . 81 

 The Avena coleoptile — Structure — Distribution of growth — Light- 

 growth reaction — Geo-growth reaction — Growth substances and 

 normal growth — Growth substances and the light-growth reaction 



