PLANT BREEDING by A. L. HAGEDOORN, Ph. D. Preface: Twenty years ago I wrote my Handbook of Animal and Plant Breeding in the Dutch language, and my Animal Breeding, grew out of the first book. The publishers have asked me to write a plant-breeding book as a companion volume to Animal Breeding with a similar scope and in the same style, and the present work is the result. As a young geneticist, I started my career as a plant-breeding consultant with the French firm of de Vilmorin Andrieux et Cie. After the first years I became more and more absorbed in matters of theoretical genetics, and during the last decade 1 have been chiefly concerned with genetics as applied to man kind and to the breeding of domestic animals. I have, how ever, never quite given up plant-breeding matters, although the only kind of practical plant breeding I have been more directly engaged upon has been the production of sugar-beet seed. This book is certainly not a textbook on Genetics, nor does it pretend to be an exhaustive treatise of everything pertaining to plant breeding. As far as possible, I have throughout the book avoided tht use of technical and scientific terms where plain English would do as well. The book is written in the first place for those who are actively engaged in the ameliora tion of cultivated plants or in the creation of plant novelties. I have quite an extensive experience of correspondence with plant breeders and amateurs, and I have often co-operated with plant breeders during some generations of their material, discussing the results obtained and helping to decide future breeding policy. This co-operation with so many people has 5 6 Plant Breeding helped to give me an understanding of apractical plant breeders difficulties, and it has afforded me some experience in explaining genetic complexities in simple terms. Plant breeding and this is especially true of plant breeding in the larger institutes is subject to fashions, and I have a notion that the preoccupation with higher mathematics is due to a certain extent to one of those fashions. I am convinced that there is very much more in selection, and even in the comparison of the yield of experimental plots, than in matters which can be ap proached only by means of slide-rules and mechanical calculators. Even though the breeding of plants nowadays is chiefly con centrated in the hands of the bigger Institutes and the more important seed firms, there are as appears from my experience large numbers of people interested in plant-breeding subjects. Apart from the host of amateur gardeners and lovers of flowers and fruit, there are thousands of amateur plant breeders, lovers of gardening who sow an occasional bed of dahlia seedlings or who raise a few hundred seedling apple-trees or seedling roses. Since I started as a plant breeder I have become greatly interested in some tropical plant-breeding problems, and as my animal-breeding book seems to have penetrated to all parts of the world, it seems to me that it is necessary to treat of the amelioration of tropical plants as well as of the breeding of plants in our temperate regions. I collected my examples in the five different countries where I have worked. The Dutch book has often been used as a textbook, and in writing the present volume I have taken this possible use into account. It is quite impossible to write a book on plant breeding without going into some technicalgenetical details, and as identical principles and phenomena are met with in both plant and animal breeding, it is unavoidable that some of the first chapters in both books treat of the same matter in much the same way. ..