PAGE 



Effects of Light on Growth 261 



Growth toward the Light; Phototropism ...... 265 



Influence of Gravity on Growth 266 



Effects of Electricity on Growth 267 



Pressure and Contact 267 



The Formation of Galls 268 



CHAPTER XVII 



GROWTH AND REGENERATION 277 



EXPERIMENTAL STUDIES IN GRAFTING 



CHAPTER XVIII 



EXPERIMENTS IN GRAFTING 285 



The Union of Different Regions ........ 285 



The Influence of the United Parts on Each Other : Formative Factors 289 



The Union of Parts of Different Species 298 



Special Problems of Development ....... 301 



EXPERIMENTAL STUDIES OF THE INFLUENCE OF 

 THE ENVIRONMENT ON THE LIFE-CYCLE 



CHAPTER XIX 



CHANGES IN THE LIFE-CYCLE AND CHANGES IN THE ENVIRONMENT . 309 



The Life Histories of Some Animals ....... 309 



Influence of Food on the Life-cycle of Lepidoptera .... 313 



Influence of the Environment on the Time of Ripening of the Sexual 



Organs 315 



CHAPTER XX 



ALTERNATION OF SEXUAL AND PARTHENOGENETIC FORMS . . . 322 

 Alternation of Generations in the Aphids and Phylloxerans . . . 322 



CHAPTER XXI 



INFLUENCE OF EXTERNAL CONDITIONS ON THE LIFE-CYCLE OF THE 



LOWER CRUSTACEANS . 336 



CHAPTER XXII 



INFLUENCE OF EXTERNAL CONDITIONS ON THE LIFE-CYCLE OF THE RO- 

 TIFER, HYDATINA SENTA 346 



