ACKNOWLEDGMENTS 



In preparing this work, the chief sources of in- 

 formation beyond the author's experience and obser- 

 vation have been the bulletins issued by the various 

 experiment stations in the United States and dis- 

 cussions in the Agricultural Press. 



For the illustrations the author is indebted to 

 Professor A. M. Soule of the experiment station of 

 Tennessee, Professor H. H. Hume of the experiment 

 station of Louisiana and Mr. W. T. Shaw of the 

 experiment station of Oregon. 



