148 
VINNIE A. PEASE 
the vertical axis representing the percent of twigs or branches ex- 
amined which bore leaves persisting for the time in years denoted on 
the horizontal axis. 
In making observations on gymnosperms, three chief points were 
considered on each twig or branch : (a) the year in which leaf fall com- 
menced; (b) the year of maximum fall, that is, the time when the 
twigs were fully half bare ; (c) the extreme duration of the last scattered 
leaves. In angiosperm species it was considered sufficient to make but 
one count for each twig or branch, and that to determine the age of the 
oldest persisting leaf. 
The factors considered as having an influence on leaf duration 
were age of the tree, light, climate, and exposure to constant winds. 
When studying gymnosperms, observations were made on mature 
trees growing in the open and in close stands, as well as on saplings 
growing in the open and under the forest cover. In angiosperm 
species, observations were made from specimens growing in the open 
and under the forest cover. The observations included natural gym- 
nosperm forest, partially cleared land, and second growth stands. 
These observations were made in the vicinity of Seattle, where the 
winds are not strong and the annual rainfall is about 36 inches. 
In order to get contrasting climatic conditions, the writer spent the 
summer of 1 91 5 at the Puget Sound Marine Station at Friday Harbor 
on San Juan Island, Washington. This island is sheltered by the 
Olympic Mountains, leaving the island an annual rainfall of less than 
25 inches. The south slopes of the island are wind-swept, the trees 
having the characteristic one-sided form common to such regions. On 
this island the Seattle observations were repeated. Also observations 
were made to see if leaf duration varied in the same species on the 
leeward and windward slopes. 
Several peat bogs in the vicinity of Seattle gave opportunity also 
to observe the effect of bog habitat on leaf duration. The observa- 
tions were made partly at the bog one-half mile east of Ronald, Wash- 
ington; partly at the Mud Lake bog, near the west shore of Lake 
Washington at 65th St., Seattle. 
Since leaf duration varies with the conditions under which the 
plant is growing, and since these conditions are matters of general 
observation rather than of accurate measurements, it follows that the 
results are general. The longest durations are for the poorest com- 
bination of conditions; the shortest duration for the best combination 
