VI CONTENTS. 



PAGE 



CHAPTER VI. IRRITABILITY. 



Irritability 183 



Physical Basis of Irritability 184 



Irritability and the Amount and Kind of Growth 186 



Influence of Gravitation 196 



Influence of Light 208 



Influence of Heat 219 



Influence of Water 222 



Influence of Other Substances 226 



Influence of Electricity 237 



Influence of Contact 239 



Conclusion 251 



CHAPTER VII. REPRODUCTION. 



Reproduction. 254 



Heredity 279 



INDEX.. . 285 



