DURATION OF LEAVES IN EVERGREENS 
149 
of conditions; and the average duration merely the average of these 
conditions as nearly as could be ascertained from all the observations 
made. Mere general observation of the external and internal con- 
ditions of tree are not sufficiently accurate to enable one to predict 
with certainty just what one will find in a given tree. 
1. Abies grandis Lindl. Shortest leaf duration observed, 2 years; 
average, 4-10 years; extreme, 14 years. All observations were made 
in the San Juan Islands, since the species is rare in the vicinity of 
Seattle. Old trees have a longer leaf duration than do saplings; 
shade tends to increase leaf duration ; the leaves of wind-swept trees 
have a shorter duration than those of protected trees {figs. 9, 10). 
2. Juniperus scopulorum Sarg. Shortest duration of green color 
observed, i year; average, 2-3 years; extreme, 4 years. The leaves, 
however, persist after turning brown. This results in the following: 
shortest leaf duration, 3 years; average, 4-6 years; extreme, 14 years. 
West of the Cascades this species occurs at low altitudes only in arid 
regions. It is quite common in the San Juan Islands. Two distinct 
types of leaves are found. The juvenile type, which are long, awl- 
shaped, and spreading, have a shorter duration than the adult, over- 
lapping scale-like type. In all cases observed, the leaves lost their 
green color from 1-4 years before they fell, and were then gradually 
sloughed off. 
3. Picea sitchensis Traut. & May. Shortest leaf duration observed, 
2 years; average, 9-11 years; extreme, 18 years. In the vicinity of 
Seattle this species was observed only in peat bogs. In the San Juan 
Islands the trees observed stand at the head of a salt marsh which 
extends up a creek bed from False Bay. Mature trees in ordinary 
soil were not available and no saplings were observed, so that the 
results given are by no means complete. 
4. Pinus contorta Dougl. Shortest leaf duration observed, 2 years; 
average, 4-6 years; extreme, 9 years. Leaf duration reported by 
Sargent (13), (14), 7-8 years; by Sudworth (17), 6-8 years. In the 
San Juan Islands, saplings in the open, and mature windswept trees, 
showed the shortest leaf duration; mature trees, protected from the 
wind, the longest duration. Trees introduced on the University 
campus showed the shortest duration observed. Sudworth states 
that "long persistence appears to belong more to young trees," but 
the writer found the opposite to be true. 
5. Piniis monticola Dougl. Shortest leaf duration observed, i year; 
