6 INTRODUCTION. 



should lead to reasonably certain conclusions : but no key in itself 

 is to be regarded as final, and determinations should be checked 

 up by reference to Bailey's Standard Cyclopedia of Horticulture, 

 in which are to be found full descriptions and references to 

 excellent illustrations. To facilitate this use, technical consid- 

 erations are waived and the names here used for genera and 

 species are conformed to the Cyclopedia : but where native 

 genera are differently named in currently used Manuals, these 

 names are added as synonyms. 



The keys do not bring together the names of genera that 

 are related ; but their division into sections dealing respectively 

 with Trees, Shrubs, Undershrubs and Cover Plants, and Climb- 

 ers, gives them a certain comparative value in addition to con- 

 venience of reference; and this is increased by the grouping in 

 various places of evergreen and deciduous, armed and spineless 

 forms, etc., and by a division of the undershrubs according to 

 their habit of growth. 



The relationships of the genera and the relative landscape 

 or other importance of families are to be seen at a glance when 

 reference is made to the systematic part of the book. An inno- 

 vation that it is hoped may prove useful, and that affords sug- 

 gestions for further observation on dependable though rarely- 

 used characters, is to be found in the brief descriptions of the 

 genera, in which more space is given to wood, bud, leaf-scar, 

 foliage and inflorescence than to the more transient details of 

 flower and fruit on which botanical classification largely rests. 



Though the manuscript has been subjected to critical use 

 by individuals and classes, it is probable that errors have been 

 overlooked, or introduced in the effort to make betterments. 

 For these, apologies are tendered ; but the hope is entertained 

 that its shortcomings may be outweighed by a general useful- 

 ness of the little handbook, which is intended to meet a need 

 that my own experience as a teacher shows to be very real now 

 that plant materials are so much studied and used. 



Urbana, Illinois, June 30, 1917. 



