De I. VNER VEW D Forest Trees of the Pacific Slope

INTRODUCTION.
This volume is the first of four which are to deal with all the
native forest trees of North America north of the Mexican boundary.
It contains an account of the tree species known to inhabit the Pacific
region, 150 in all. Part II will be devoted to the Rocky Mountain
trees, Part III to the trees of the southern States, and Part IV to the
trees of the northern States.
The region covered by Part I includes Alaska, British Columbia,
Washington, Oregon, and California (see ma~ps, frontispiece). Many
trees described occur wholly within this region, but none are represented
throughout it. A few are found on its southern border and
range into Mexico, while three or four trees stretch from within the
Pacific region to the Atlantic.
DEFINITION OF A TREE.
The definition of a tree followed by the author includes woody
plants having one well-defined stem and a more or less definitely
formed crown (but not excluding unbranched cactuses, yuccas, and
palms), and attaining somewhere in their natural or planted range
a height of at least 8 feet and a diameter of not less than 2 inches.
It has been difficult to apply this definition in all cases, for there is
no sharp line between some shrub-like trees and some tree-like
shrubs. However, though wholly arbitrary, it has been serviceable.
A considerable number of species included are, over much of their
range, little more than chaparral shrubs, becoming tree-like only
in exceptionally favorable places. Recent discoveries in this region
have made it necessary to class as trees several species previously
regarded as shrubs. Some species are shrubs within this territory,
but are trees outside of it. There still remain for further careful
consideration several species of Arctostaphylos, Ceanothus, and
Styrax, which may prove to be trees.
DESCRIPTIONS AND ILLUSTRATIONS OF SPECIES.
Since this work was prepared solely for the layman, the use of
technical terms has been avoided. In describing species the writer
has endeavored to define essential and simple characters in plain
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