PREFACE XV 



technical terms as far as possible will be 

 avoided, with the exception, however, of 

 the scientific names of the parasites. Pop- 

 ular terminology does not always distin- 

 guish between diseases of different nature 

 that are apparently alike. For example, 

 the term "blight" is applied to diseases of 

 similar symptoms but of quite different 

 causes. Methods of controlling a disease 

 are directly dependent on a knowledge of 

 the nature and cause of the particular 

 trouble. Taking insect pests as an exam- 

 ple, it is essential to know whether they 

 are biting or sucking, each class requiring 

 different treatments. 



The writer feels that no apology is 

 needed for allowing space in this book to 

 a discussion of the culture of the sweet 

 pea. No matter from what angle we look 

 at it, we cannot deny the fact that plant 

 diseases are directly dependent on the cul- 



