Preface to Fourth Edition 



In the revision for the present edition an attempt 

 has been made to bring this httle book up to the best 

 knowledge and practice of the day. I am under 

 special obligations to Professor L. R. Jones for the 

 revision of the part treating of potato enemies, to 

 Professor F. A. Waugh for reading the proof through- 

 out, and to Mr W. E. Britton for the loan of the 

 electrotype used on page io6. Of course I am under 

 obligations also to the great number of workers who 

 have made possible the wonderful advance in spraying 

 operations during recent years. A book like this can 

 only hope to be a compilation of the results of many 

 minds, and I have not hesitated to draw freely from 

 many sources, giving due credit so far as practicable. 

 To all who have thus contributed to the possible use- 

 fulness of the book I extend cordial thanks. 



C. M. W. 



Durham, N. H., May, 1903. 



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