xviii CONTENTS 



PAGK 



3. General Considerations 444 



a. Persistence of Stimulation 444 



b. Acclimatization to Light 444 



e. Mechanics of Phototropism 444 



Literature 445 



CHAPTER XVIII 

 Effect of Heat on Growth 



§ 1. Effect of Heat on the Rate of Growth 450 



1. Plants 450 



2. Animals 457 



3. Some General Phenomena accompanying Heat Effects . . 460 



a. Latent Period 460 



h. Sudden Change of Temperature ..... 460 



c. Cause of Acceleration of Growth by Heat . . . 461 



§2. Effect of Heat on the Direction of Growth — Thermotropism . 463 



1. Effect of Radiant Heat 463 



2. Conducted Heat 464 



3. Causes of Thermotropism 466 



Summary of the Chapter 467 



Literature 407 



CHAPTER XIX 



Effect of Complex Agents upon Growth, and General 

 Conclusions 



§ 1. The Cooperation of Geotropism and Phototropism . . . 470 



§ 2. Effect of Extent of Medium on Size . . . . 473 



§ 3. General Considerations relating to the Action upon Giowth of 



External Agents 478 



1. Modification of Rate of Growth .... . 478 



2. Modification of Direction of Growth — Tropism . . . 480 



3. Adaptation in Tropisms 484 



4. Critical Points in Tropism ....... 484 



Literature 486 



List of Tables in Parts I and II 489 



Index to Parts I and II 493 



