156 
VINNIE A. PEASE 
dicotyledonous tree; and Copeland (i) in his study on the size of ever- 
green needles found that in abnormal years, when the leaves are small, 
''the number of needles compensates the plant for their lack of size, 
sometimes furnishing an even greater surface of leaf than is borne on 
the normal year's growth of stem." Following the same line of 
thought, it may be that the longer duration of leaves on mature trees, 
or on trees growing under adverse conditions, which is correlated with 
a decrease in size, tends to keep up the total leaf area. With longer 
duration and smaller leaves in dense shade as compared with open 
situations, increased duration may be correlated with two factors. 
Reduced size of the individual leaf, and reduced photosynthetic ac- 
tivity, due to diminished light intensity, are both compensated by an 
increased number of leaves; and increased leaf duration would furnish 
this increase in the number of leaves. 
In all angiosperm forms which were examined, both in the open and 
in the shade, the leaves on shaded plants were much larger than those 
on plants exposed to direct sunlight; and with the exception of Gaul- 
theria shallon growing in the typical climatic conditions of the vicinity 
of Seattle, plants in the shade held their leaves longer than those in 
the open. Hasselbring (6), in commenting on his experiments with 
Cuban tobacco grown under a cheese-cloth shade, states that "the 
reduction in photOvSynthesis in the shade leaves was compensated by 
an increase in leaf area, so that the production was not diminished." 
In various species under discussion, it is quite possible that the increase 
in photosynthetic area, which compensates the decrease in light in- 
tensity, is due not only to the increased size of the leaves but also to 
their increased duration. 
Conclusions 
1. Leaf duration varies widely among the different evergreen 
species, ranging from Rhamnus purshiana, which in young plants 
sometimes holds part of the leaves of one season until those of the next 
season are mature, to Taxus hrevifolia, which has an extreme leaf 
duration of 23 years. 
2. Leaf duration varies widely in individuals of the same species of 
different age or growing in different habitats: (a) Saplings have a 
shorter leaf duration than mature trees in the same habitat, {h) Trees 
or shrubs growing in the open have a shorter leaf duration than those 
of similar age in the shade, {c) Trees or shrubs on a windward coast 
have a shorter leaf duration than those on a leeward coast, {d) Gym- 
