DURATION OF LEAVES IN EVERGREENS 
nosperms in a moist climate have a shorter leaf duration than those in 
a drier climate, (e) A peat bog habitat has an effect similar to a dry 
climate. 
3. Those factors which cause slowness of growth, and thus only a 
slight increase in diameter of the axis, are accompanied by an increased 
duration of the leaves. 
4. Under the same climatic conditions, those factors which cause 
an increase in transpiration are accompanied by a decrease in leaf 
duration, and thus by a decrease in the transpiring surface. 
5. Those factors which cause a decrease in photosynthetic activity 
are accompanied by an increase in leaf duration, and thus by an 
increase in the photosynthetic area. 
6. It is quite possible that the variations in leaf duration in a given 
species may be due to differences in transpiration or photosynthetic 
activity, caused by difference in age or habitat. 
University of Washington, Seattle 
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