CONTENTS 



CHAPTER I 

 INTRODUCTION 



PAGE 



The founders of the art of plant breeding 2 



The first demonstration of sex in plants 3 



Further proof of plant sexuality 4 



The studies of Koelreuter 5 



Early studies of the cytology of fertilization 5 



An answer to the question of hybrid fertilization 5 



The great hybridist Gartner 6 



Early English plant breeders 6 



Other workers of this period 7 



The relation of certain biologic principles to plant breeding 8 



The doctrine of the constancy of species 9 



Darwin's theory of natural selection 9 



The stability of the germ plasm 10 



DeVries' mutation theory 11 



The pure-line theory 11 



Mendel's law of heredity 12 



Hybridization as a means of producing variations 13 



The value of crop improvement in relation to a more efficient agriculture 14 



CHAPTER II 

 PLANT GENETICS 



Methods of studying inheritance of characters 16 



The mode of sexual reproduction in flowering plants 17 



The inheritance factors 20 



Variability of characters 20 



A cross in which the parents differ by a single factor 22 



Inheritance of two independently inherited characters 23 



Several factors necessary for the production of a character 25 



Linkage of characters in inheritance 26 



Inheritance of quantitative characters 27 



Stability of inherited factors 32 



CHAPTER III 

 THE MODE OF REPRODUCTION IN RELATION TO BREEDING 



Natural crossing with self -fertilized plants 34 



Wheat, 34; Barley, Oats, Tobacco, Flax, 36; Rice, 37; Cotton, 

 Grain Sorghums, Peas and Beans, 38; Tomatoes, 39. 



The often cross-pollinated plants 39 



Maize, Rye, 39; Alfalfa, 40; Grasses, 41. 



xi 



