xviii CONTENTS 



PAGE 



3. General Considerations . . . 444 



a. Persistence of Stimulation 444 



b. Acclimatization to Light . . . . . . 444 



c. 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 



b. 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 4G7 



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 Growth 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 



