Optional Study 4. Autumnal Coloration and Leaf Fall
Probably the grandest phenomenon of nature that is peculiar to our northern latitude, is the coloration of the woods in autumn. All marvel at the display. Few observe it carefully. It is the object of this study to direct attention to some of the external features of it: the mechanical preparation of the leaf for its fall, the changing pigments of the residual leaf contents, and the relation of these changes to temperature and rainfall, etc. The whole process is a wonderful adaptation to meet winter conditions, and how admirably nature manages it! She first withdraws all food materials from the leaves into the stem and branches. Then she starts her wonderful display by elaborating bright pigments out of the residue. Then she casts the leaves off in an orderly fashion, developing breaking points at proper places. So she diminishes to a very small percentage the area of exposed evaporating surfaces, and thus she conserves moisture in the plant body through the long cold season. The changing hues of autumn are more or less accidental byproducts of this process; but they are very beautiful.
The work of this study should include serial observations on a dozen or more of the more brilliantly colored species, continued from the first appearance of an autumn tint until the last of the leaves have fallen. The same trees should be observed day by day, account being taken of the relevant weather conditions. Hence, trees, shrubs and vines near at hand should be chosen. Those on the lawn are apt to be as good as any, since ornamental planting in our day takes careful forethought for the autumnal display.
