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. 
