viii AUTHOR'S PREFACE 



Agriculture (Part II) : to Sir Francis Watts for valuable help in 

 preparing the chapter on fungicides ; to Miss E. M. Wakefield, 

 of the Royal Gardens, Kew, for kindly assisting in proof 

 reading, and Mr. S. F. Ashby, for assistance with the biblio- 

 graphy and illustrations ; to Dr. J. B. Farmer, F.R.S., Professor 

 of Botany at the Imperial College of Science and Technology, 

 not only for the immediate contribution of an introduction, but 

 in a special sense as the director of a course of biological 

 training in which information is held subordinate to essential 

 principles. The writer must further gratefully acknowledge 

 that without the constant assistance of his wife the labour 

 of writing could never have been faced in the time available 

 from other duties. 



