CONTENTS xvii 



CHAPTER XV 

 EFFECT OF GRAVITY UPON GROWTH 



PAGB 



1. Effect of Gravity upon the Rate of Growth 391 



2. The Effect of Gravity upon the Direction of Growth Geotropism 391 



1. False Geotropism 392 



2. True Geotropism -392 



a. Roots 392 



6. Stems 397 



c. Rhizoma 398 



d. Cryptogams 398 



e. Animals 398 



/. After-effect in Geotropism 401 



Summary 402 



Literature 403 



CHAPTER XVI 

 EFFECT OF ELECTRICITY UPON GROWTH 



1. Effect of Electricity upon the Rate of Growth .... 405 



2. Effect of Electricity upon the Direction of Growth Electro- 409 



tropism 409 



1. False and True Electrotropism 409 



2. Electrotropism in Phanerogams . . . . . .411 



3. Electrotropism in Other Organisms . . . . .412 



4. Magnetropism . . . . . . . . . .413 



5. Explanation of Electrotropism and Summary . . . 413 

 Literature ' 414 



CHAPTER XVII 

 EFFECT OF LIGHT UPON GROWTH 



1. Effect of Light on the Rate of Growth 416 



1. Retarding Effect of Light 416 



2. Accelerating Effect of Light . . . . . . .423 



3. The Effective Rays 427 



a. The Effective Rays in the Retardation of Growth by Light 427 



&. The Effective Rays in the Acceleration of Growth byLight 432 



4. The Cause of the Effect of Light on the Rate of Growth . 436 

 2. Effect of Light upon the Direction of Growth Phototropism . 437 



1. Plants 437 



2. Animals . 442 



a. Serpulidae ......... 442 



b. Hydroids 443 



