iv INTRODUCTION 



Dr. G. E. Stone has also furnished photographs, 

 and has been so good as to spend much time ex- 

 plaining his interesting experiments and the work 

 of his students at the Massachusetts Agricultural 

 College. Mr. A. T. Hastings, Jr., City Forester 

 of Jersey City, has very kindly supplied photo- 

 graphs. To these, and many others, the writer 

 gratefully acknowledges his indebtedness. 



