Vlll PREFACE 



or processes which could be better understood when correlated with the 

 other soil organisms and the numerous other processes. An attempt 

 has been made to compile a book which will be of service not only to the 

 investigators in soil science, but also to workers in allied sciences, 

 especially botany, plant physiology, plant pathology and bacteriology, 

 as well as to the general student in agriculture. 



This book is a collection of known facts concerning microorganisms 

 found in the soil and their activities; it is a study of the literature dealing 

 with the science in question; it is an interpretation of the facts already 

 presented; it indicates the various lines of investigation and notes where 

 further information is especially wanted. Soil microbiology is a science 

 which is at the very base of our understanding of agricultural processes 

 and the practice of agriculture; it comprises a number of sciences. The 

 book may, therefore, be looked upon more as an introduction to further 

 research rather than as an ordinary text-book; as of help to those work- 

 ing in the allied sciences, who are desirous of obtaining some information 

 concerning the soil population and its activities. 



If this volume will help to disclose to the reader some of the numerous 

 interrelated processes in the soil, if it will present in a clearer light to the 

 chemist, the physiologist, the botanist, the bacteriologist and the 

 zoologist the nature of the many scientific and practical problems 

 awaiting the investigator, if it contributes in a small measure toward 

 making soil science an exact science, the author will feel that he has been 

 amply rewarded. 



The author is greatly indebted to his various colleagues for reading 

 and criticizing the different chapters of the book and for the many 

 helpful suggestions generously offered, especially to Dr. H. J. Conn, of 

 the New York Agricultural Experiment Station, for reading Chapters 

 I and VI; to Dr. B. M. Bristol Roach, of the Rothamsted Experimental 

 Station, and Dr. G. T. Moore, of the Missouri Botanical Garden, for 

 reading the Chapter on Algae; to Dr. Ch. Thorn of the Bureau of 

 Chemistry, for reading the Chapter on Fungi; to Dr. M. C. Rayner, of 

 Bedford College, London, for reading the section dealing with Mycor- 

 rhiza Fungi; to Dr. A. T. Henrici, of the University of Minnesota, 

 for reading the Chapter on Actinomyces; to Dr. W. M. Gibbs, of the 

 Idaho Agricultural Experiment Station, for reading the Chapter on 

 Nitrifying Bacteria; to Dr. A. L. Whiting, of the University of Wis- 

 consin and to Dr. L. T. Leonard of the Bureau of Plant Industry, for 

 reading the Chapter on Nodule Bacteria; to Dr. R. Burri, of Liebefeld, 

 Switzerland, and to Dr. I. C. Hall, of the Colorado Medical School, 



