ACKNOWLEDGMENTS 



The author is under obligations to many friends for helpful 

 suggestions and illustrations. Especial credit is due the following 

 for illustrations used on the pages indicated : Professor E. O. Pippin, 

 of Cornell University, 29. 31, 34, 36, 65, 91, 94, 113, 173, 174, 192, 

 195, 198, 204, 218, 236, 266, 280, 283, etc. ; Professor A. M. Ten Eyck, 

 of the Kansas Experiment Station, 2, 13, 20, 47, 197, 270; Professor 

 Oscar Erf, of Kansas Experiment Station, 207, 209, 211, 259; 

 Professor Charles E. Thome, Director of the Ohio Experiment 

 Station, 100, 105 : Dr. C. G. Hopkins, of the Illinois Experiment 

 Station, 267, 268; Mr. George K. Helder, 177. 178, 180, 182, 183, 194, 

 202. Thanks are also due the Orange Judd Company for many 

 photographs and Mr. B. F. Williamson for the line drawings. 



