CONTENTS 



xvii 



CHAPTER XV 



Effect of Gravity upon Growth 



§ 1. Effect of Gravity upon the Kate of Growth . 



§ 2. The Effect of Gravity -upon the Direction of Growth — Geotropism 



1. False Geotropism . 



2. True Geotropism 



u. Koots 

 I. Stems 



c. Khizoma . 



d. Cryptogams 



e. Animals . 

 /. After-effect in Geotropism 



Summary .... 

 Literature 



PAGE 



391 

 391 

 392 

 392 

 392 

 397 

 398 

 398 

 398 

 401 

 402 

 403 



CHAPTER XVI 



Effect of Electricity upon Growth 



§ 1. Effect of Electricity upon the Rate of Growth 

 § 2. Effect of Electricity upon the Direction of Growth' 

 tropism ... 



1. False and True Electrotropism 



2. Electrotropism in Phanerogams 



3. Electrotropism in Other Organisms 



4. Magnetropism . 



5. Explanation of Electrotropism and Summary 



- Electro- 



Literature 



405 

 409 

 409 

 409 

 411 

 412 

 413 

 413 

 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 



u. TheEffectiveRaysintheRetardation of Growthby Light 427 



6. TheEffectiveRaysinthe Accelerationof GrowthbyLight 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. Serpulidse 442 



J. Hydroids ... 443 



