xiv CONTENTS 



PAGE 



Organizations of plant breeders 300 



Summary 301 



CHAPTER XVI 

 ON VARIETIES IN PLANTS 



Introductory 302 



Extent of variety differentiation in plants 302 



The origin of domestic varieties of plants 302 



Origin of sweet pea varieties 303 



Flower color in sweet peas 304 



Form and size in sweet peas 304 



Habit in sweet peas 308 



Hybridization and selection in the sweet pea 309 



Creation of varieties of the rose 310 



Origin of varieties in the Boston Fern 312 



CHAPTER XVII 

 THE COMPOSITION OF PLANT POPULATIONS 



Introductory 317 



Reproduction in plants 317 



Plants normally self-fertilized 317 



Plants normally cross-fertilized 317 



Discussion 318 



Populations of plants normally self-fertilized 320 



Populations as affected by crossing 321 



Summary 324 



CHAPTER XVIII 

 SELECTION 



Introductory 325 



Selection methods in maize breeding 325 



Inbreeding in maize 325 



The ear-to-row method 327 



The Illinois Station experiments 327 



The remnant system 335 



Selection methods in close-pollinated plants 336 



The plant-to-row method 337 



Ineffectiveness of continued selection within pure lines 339 



The practical importance of keeping varieties pure . . 341 



CHAPTER XIX 



HYBRIDIZATION 

 Introductory 342 



