DURATION OF LEAVES IN EVERGREENS 
Plants growing in the shade about the borders of the bog were much 
modified, being much taller; and with leaves larger, thinner, less 
revolute, and less densely clothed with hairs on the under surface. 
These leaves were of much longer duration. 
28. Oxy coccus oxy coccus intermedins Piper. Shortest leaf duration 
observed, i year; average, 2-3 years; extreme, 4 years. Plants parti- 
ally shaded by the taller growth of Ledum about the hemlock hillocks 
showed* increased leaf duration. 
29. Pachistima myrsinites Raf. Shortest leaf duration observed, 
2 years; average, 3-4 years; extreme, 8 years. This species was ob- 
served only in the San Juan Islands. Plants growing in exposed 
locations on the windward side of the islands had a shorter leaf duration 
than those on the leeward side. 
30. Rhododendron calijornicum Hook. Shortest leaf duration 
observed, i year; average, 2 years; extreme, 3 years. This plant was 
observed only on the university campus, where it is used extensively 
as an ornamental shrub. 
31. Vaccinium ovatum Pursh. Shortest leaf duration observed, 
2 years; average, 2-4 years; extreme, 7 years. Plants in the shade 
show a decided increase in leaf duration {figs. 13). 
It has already been noted that in many of the gymnosperms growing 
under adverse conditions, that is, in dense shade or in peat bogs, leaves 
are smaller and fewer in number on a year's growth than on specimens 
of the same species growing under more favorable conditions. While 
the tendency is not so marked in all cases the same difference in size 
was noted between the leaves of mature trees and those of saplings, 
mature trees ordinarily having smaller leaves than those of saplings. 
Kraus (9) observed that the length and vigor not only of the grow- 
ing shoots but also of the needles vary in different seasons; and Reinke 
(12) demonstrated that in transplanted evergreens the needles formed 
during the growing season immediately following the transplanting 
are conspicuously shorter than those formed during either the pre- 
ceding or the following season. This was afterward confirmed by 
Copeland (i), who measured the needles on transplanted evergreens 
on the campus of Indiana University. Former observations are thus 
extended to include the variation in size of leaves on trees of the same 
species of different age, or growing in different habitats. 
Groom (5) observed that though the individual leaf is small, the 
aggregate leaf surface of the conifer often greatly exceeds that of the 
