BREEDING CROP PLANTS BY HERBERT KENDALL HAYES PROFESSOR OF PLANT BREEDING, - PREFACE Since the early development of agriculture by primitive peoples, selection of seed for planting has been an important feature of agricultural practice. While many of our better varieties or strains of crop plants have originated as chance seedlings orfrom selections made bymen who lacked a knowledge of the laws of heredity, there has been a growing appreciation in recent years of the value of training students for the occupa- tion of plant breeding. Studies in crop genetics carried on since 1900, as well as studies in field plot technic, have helped in a large measure to standardize methods of breeding. Information regarding the mode of inheritance of particular characters as well as a better knowledge of the wild relatives of our crop plants is con- stantly being obtained. The purpose of this book is to present fundamental principles of crop breeding and to summarize known facts regarding the mode of inheritance of many of the important characters of crop plants. Much of the material here presented has been used in courses in crop breeding which have been given in recent years at the College of Agriculture, of Minnesota. University Suggestions from others in relation to methods of treatment of various subjects have been of material value. Particular mention should be made of the helpful advice of Dr. M. J. Dorsey regarding the chapters on Plant Genetics and Fruit Breeding of F. A. Krantz regarding the chapter on Potato Breeding, and of John Bushnell and W. T. Tapley regarding the chapter on Vegetable Breeding. We are also indebted to Miss Alice McFeely, Bulletin Editor, for many suggestions regarding presentation and for assistance in proofreading to Mr. A. N. Wilcox for assistance in proofreading to Miss L. Mae Centerwall for help in obtaining a considerable number of publications from other libraries and to Miss Alma Schweppe for checking the literature citations. Pre- vious summaries of certain phases of plant breeding methods were IX