PREFACE TO THE SECOND EDITION vii 



Rhoderick Sprague who read the rough draft after revision ; to Dr. L. 

 L. Ashburn who read Chapters VI and VII; to Dr. H. Koepsell who 

 read portions of Chapter XI; and to Dr. S. A. AVaksman and Dr. 

 Charles Drake who read Chapter XIII. Thanks are due Dr. L. G. 

 Romell, Experimentalfaltet, Sweden, who in the face of great diffi- 

 culties got through to us much information on Bjorkman's theory of 

 mycorrhiza, and to Dr. W. P. Larson, "Chief" to Dr. Henrici and to 

 two of us, who suggested the revision and encouraged its completion. 

 We wish to thank Dr. Sprague, Dr. N. H. Huff, Dr. Kenneth Raper, 

 and Miss Hazel Jean Henrici for original drawings and photographs; 

 also the following holders of copyrighted figures and tables, each of 

 which is credited to the author in the text: Macmillan and Company, 

 Ltd., Dr. Fred J. Seaver, Phytopathology, Williams and Wilkins Co., 

 Minnesota Agricultural Experiment Station, American Medical Asso- 

 ciation, New York Botanical Garden, W. B. Saunders Co., United 

 States Department of Agriculture, Dr. S. A. Waksman, Dr. R. L. 

 Starkey, and Dr. J. R, Porter. 



August, 1945 



