PREFACE Vll 



Mfg. Company, Southport, Conn., for illustration 

 No. 28; to C. B. Sayre of Purdue University for illustra- 

 tions Nos. 29, 68, 81, 136, 137 and 138 ; to the Bureau of 

 Plant Industry for illustrations Nos. 35 and 36; to the 

 United States Department of Agriculture for illustration 

 No. 39 ; to the Ohio Agricultural Experiment Station for 

 illustration No. 53; to E. F. Stoddard of the Maryland 

 Agricultural College for illustration No. 66 ; to the Ten- 

 nessee Experiment Station for illustrations Nos. 76 and 

 77 ; to Sutton and Sons of Reading, England, for illustra- 

 tions Nos. 80, 92, 125 and 126; to G. L. Tiebout of the 

 Louisiana College of Agriculture for illustration No. 84 ; 

 to David Lumsden formerly of New Hampshire College, 

 now of Cornell University, for illustrations Nos. 91, 95 and 

 104; to L. M. Montgomery of Ohio State University for 

 illustrations Nos. 127 and 129; to W. H. Weinschenk of 

 New Castle for illustration No. 134; to the Virginia 

 Truck Experiment Station for illustration No. 139; and 

 to C. G. Woodbury of Purdue University for illustration 

 No. 146. 



