viii INTRODUCTION 
and leaf-scars, particularly those of ordinary branches rather 
than suckers or spurs, before beginning to use the key. When 
this practice is followed, after a few familiar species have 
been traced through so as to give facility, the key will be 
found simple, direct and conclusive in nearly every case; and 
native and introduced species, as well as genera, may be 
named for the most part. 
The present volume, though conifers are excluded, deals 
with 326 genera belonging to 93 families. Species and espe- 
cially varieties are not differentiated to the same extent as in 
the earlier volume, but the keys lead to the names of about 
1100 such forms. ; 
As in the earlier volume, questions of nomenclature have 
been waived, and the same names are used in both books 
except for correction of a few oversights in the first, so that 
reference may be made readily to the Standard Cyclopedia for 
other information concerning the plants; and this is even 
more necessary than when names are learned from summer 
characters. 
