vi CONTENTS 



VIII. Relation of Genes to Characteristics 179 



IX. Rules and Ratios of Inheritance 206 



X. Relation of Characteristics to En- 

 vironment 232 



Its Interaction with Heredity 



XI. Effects of Mixing Diverse Organisms. 



Hybridization 266 



XII. General Relations in the Operation 

 OF the Genetic System Through 

 THE Passage of Generations 283 



XIII. Genetic Variations 315 



Changes in the Structure and Operation 

 of the Genetic System 



XIV. Genetic Variations 340 



Changes in the Operation of Single Genes. 

 Mutations 



Index 367 



