INTRODUCTION. 11 



their entirety and photographed against an appiopriate background, 

 many others were drawn in place. In the drawings the root systems 

 are arranged as nearly as possible in the natural position in a vertical 

 plane. The sketching was first done with pencil on a large drawing- 

 sheet ruled to scale. Drawings were made simultaneously with the 

 excavating of the roots and always to exact measurement. When 

 entirely completed they were retraced with India ink. Such drawings, 

 carefully executed, often represent the extent, position, and minute 

 branching of the root system even more accurately than a photograph, 

 for under the most favorable conditions, especially with extensive 

 root systems, the photograph is always made at the expense of detail, 

 many of the finer branches and root-ends being obscured. 



The writer wishes to acknowledge the faithful assistance of Miss 

 Annie Mogensen in the execution of many of the drawings. He is 

 also indebted to Professor J. C. Russel, of the Nebraska Experiment 

 Station, for soil analyses, and to Dr. J. 0. Belz, of the United States 

 Bureau of Plant Industry, for the determination of wilting coefficients. 

 It is a pleasure to acknowledge the helpful suggestions given by Dr. 

 F. E. Clements and Dr. R. J. Pool throughout the period of the work. 

 To both Doctor Clements and Professor T. J. Fitzpatrick the writer is 

 indebted for careful reading of the manuscript and proof. 



