150 
■ VINNIE A. PEASE 
average, 3-4 years; extreme, 6 years. Leaf duration reported by 
Sargent (13), 3-4 years. This species, found commonly in the Puget 
Sound region in peat bogs, showed the shortest duration of any of the 
gymnosperms studied. Mature trees show a tendency to hold their 
leaves longer than do saplings. 
6. Pseudotsuga taxifolia Britton. Shortest leaf duration observed, 
I year; average, 3-9 years; extreme, 16 years. Leaf duration reported 
by Groom (4), Sargent (14) and Sudworth (17), about 8 years; by 
Ward (19), 6-7 years. Observations showed that saplings have a 
much shorter leaf duration than do mature trees; trees in the open have 
a much shorter leaf duration than those in the shade; wind-swept 
trees have a short leaf duration; a dry climate increases leaf duration; 
a peat bog habitat increases the duration of leaves in saplings to a 
greater degree than does a dry climate. No observations were made 
on mature trees in peat bogs. A winter season of unusual severity, 
such as that experienced by the Pacific northwest in January and 
February, 1 916, when snow lay on the branches for several weeks, 
seriously affects the duration of the leaves. Thirty-eight percent of 
the branches examined showed partial loss of the leaves of the pre- 
ceding season's growth, whereas no such loss was observed on the same 
trees during the same period of the preceding year. It was noted also 
that, in specimens of Pseudotsuga taxifolia growing in dense shade, 
the annual thickening of the trunks was very slight, the leafy twigs 
were very slender, and the needles small and comparatively few on a 
year's growth {figs. 1-5). 
7. Taxus brevifolia Nutt. Shortest leaf duration observed, 2 
years; average, 5-12 years; extreme, 23 years. Leaf duration re- 
ported by Sargent (14), 4-5 years; by Sudworth (17), 6-9 years. 
A summary of the effects of varying external conditions cannot be 
given since not enough data could be secured. However, in ordinary 
conditions of moisture for the Puget Sound region, and in densely 
shaded locations in the drier climate of the San Juan Islands, the 
duration of leaves has been found to be much greater than previously 
supposed. 
8. Thuja plicata Donn. Shortest duration of green color, i year; 
average, 2-5 years; extreme, 7 years. Since the leaves persist after 
losing their color the duration is longer than given above. Observa- 
tions resulted in the following: shortest leaf duration observed, 3 years; 
average, 4-7 years; extreme, 12 years. Leaf duration reported by 
