PREFACE 



This book has been written in an attempt to bring 

 together the knowledge necessary to answer (as far as possi- 

 ble) the many technical questions which the plant lover may 

 ask about growing plants. It is an attempt to make clear 

 the "how and why" of plant growth. The principles of the 

 laws of nature as applied to plants growing in the soil are 

 stressed. Many of the newer theories used in plant culture 

 are described; others, not so well established, are suggested 

 as possible future developments. The illustrative material 

 has been selected, when possible, because it is found around 

 most homes, and can be examined by the reader. 



The privilege of using numerous illustrations, as acknowl- 

 edged in each case, has been highly valued. The careful 

 work of Mrs. Marian Manning in making the original photo- 

 graphs is deeply appreciated. 



The author is happy to thank Dr. R. F. Griggs and Dr. 

 Mary Reid for frequent encouragement and suggestions dur- 

 ing the preparation of the manuscript. For the suggestions 

 and the improvement of the chapters on plant breeding he 

 expresses his heartfelt appreciation to Dr. and Mrs. Jack R. 

 Harlan. The author is deeply indebted to his many teachers, 

 students, and associates who have helped him to get the 

 necessary knowledge to attempt a work of this kind. 



The critical reading of the manuscript and the many 

 helpful suggestions of my wife, Mildred Yocum, are most 

 deeply appreciated. 



L. Edwin Yocum 



