VI PREFACE 



The bibliographies are obviously incomplete. Most of the 

 titles were made use of by the writer in the preparation of the 

 manuscript, and to the authors of these he is under obliga- 

 tion. Bailey's Cyclopedia of Horticulture has been indis- 

 pensable and has been called into use frequently. The 

 writer has also called upon the publications of the United 

 States Department of Agriculture and of the various Experi- 

 ment Stations. A number of the "keys" are original, 

 many are adapted, and a few are taken verbatim. A 

 majority of the illustrations are original. It is believed that 

 the direct method adopted herein of labeling drawings will 

 appeal to both students and teachers. 



Almost all original illustrations, and also those copied or 

 adapted are the work of Mr. N. Lee Foster. The writer is 

 especially indebted to him, not only for the delineation, but 

 for his helpful interest and valued cooperation throughout. 

 Professor D. W. Frear, formeily Associate Professor of 

 Agronomy at the Colorado Agricultural College, now of the 

 North Dakota Experiment Station, is to be given credit for 

 organizing and writing up portions of Chapters IX, XVII, 

 XXX and XXXVIII. The text was planned and outlined 

 by Professor Frear and the undersigned as joint authors, 

 but unavoidable exigencies made it impossible for him to 

 continue his connection as author. The entire manuscript 

 was painstakingly read by Louise Falk Robbins, and her 

 suggestions have added greatly to the accuracy in many 

 places, 



W. W. Robbins. 



Colorado Agricui-tural College 



