PREFACE. 



I wish to express my appreciation of the guidance of Professor 

 I. P. Roberts, Professor G. C. Caldwell and Professor Thomas 

 F. Hunt, who constituted the committee having my work in 

 charge, also of the advice given by Dean L,. H. Bailey and the 

 assistance of Mr. G. N. Lauman. For the analytical work, 

 extending through a period of seven years and involving several 

 thousand chemical determinations, I am indebted to Professor S. 

 Avery, Mr. R. S. Hiltner, Professor R. W. Thacher, Mr. Y. 

 Nikaido, Miss Rachael Corr, Mr. H. B. Slade and Mr. G. H. 

 Walker. Mr. Alvin Keyser has kept records of the wheat 

 breeding plats and Mr. E. G. Montgomery has assisted in 

 keeping other records. 



192221 



