xvi CONTENTS 



CHAPTER XII 

 The Effect of Water upon Growth 



PASS 



§ 1. Effect of Water upon the Rate and Quantity of Growth . . 350 



§ 2. Effect of Water on the Direction of Growth — Hydrotropism . 355 



1. Roots 356 



2. Rhizoids of Higher Cryptogams .... . 357 



3. Stems ... 358 



4. Pollen-tubes 358 



5. Hyphse of Fungi . . 358 



Literature 360 



CHAPTER XIII 



Effect of the Density of the Medium upon Growth 



§ 1. Effect of Density upon the Rate of Growth .... 362 



Literature 369 



CHAPTER XIV 

 Effect of Molar Agents upon Growth 



§ 1. Effect of Molar Agents upon the Rate of Growth .... 370 



1. Contact 370 



2. Rough Movements . . . .... 370 



3. Deformation 372 



4. Local Removal of Tissue ....... 375 



§ 2. Effect of Contact upon the Direction of Growth — Thigmotropism 376 



L Twining Stems 376 



2. Tendrils 377 



3. Roots . . 380 



4. Cryptogams . . . . . . 381 



5. Animals ........... 382 



6. The Accumulation of Contact-stimulus and Acclimatization 



to it 382 



7. Explanation of Thigmotropism . ... 383 

 § 3. Effect of Wounding upon the Direction of Growth — Trauma- 



tropism 384 



1. False Traumatropism . ...... 384 



2. True Traumatropism .... ... 384 



§ 4. Effect of Flowing Water upon the Direction of Growth — Rheo- 



tropism 387 



Summary of the Chapter 388 



Literature 389 



