DURATION OF LEAVES IN EVERGREENS 
ViNNiE A. Pease 
While the duration of leaves in evergreens is not at all a new subject, 
very little systematic work seems to have been done toward determin- 
ing durations for an extended list of evergreen species. This work was 
begun for the purpose of determining the leaf duration of the evergreen 
species of trees and shrubs in western Washington. It soon developed 
that the work would not be a mere cataloging of species with their 
accompanying leaf durations, since a very superficial examination of 
some of the coniferous evergreens growing under different conditions 
on the University campus, showed a wide but constant difference in 
the duration of their leaves. It was then decided to limit the species 
discussed to those growing under varying conditions that could be 
examined in the field, and to ascertain, if possible, the factors governing 
the duration of their leaves. 
The Pacific northwest is peculiarly an evergreen region. Sargent 
(15) described the characteristic coniferous forests as the most luxuriant 
if not the most diversified on the continent. His report in the Tenth 
Census states that "Washington is covered with the heaviest con- 
tinuous belt of forest growth in the United States. This magnif- 
icent coniferous forest extends over the slopes of the Cascade and 
Coast ranges, and occupies the entire drift plain surrounding the waters 
of Puget Sound." Evergreenness is not only characteristic of the 
forests, but is equally typical of the forest undergrowth, and of a large 
list of herbaceous species of the open fields. This is especially true 
of the Puget Sound region, in which the mild climate affords a practic- 
ally continuous growing season. This may be one reason why many 
species elsewhere deciduous are here evergreen. 
There are, in the state of Washington, according to Frye and Rigg 
(2), 76 species of woody evergreens, 24 of which are gymnosperms, and 
52 angiosperms. In western Washington there are 52 species, 16 of 
which are gymnosperms, and 36 angiosperms. Of these the writer 
has studied the following 9 gymnosperms and 22 angiosperms: 
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