THE CHANGING COLOUR OF THE AUTUMN WOODS
All through the autumn, when the wonderful colours come in the forest leaves, we shall see the green of these leaves creeping back along the veins. The horse chestnut leaves tell a very interesting story. They turn brown first upon the edges. If we watch a single leaf for a whole week in September, we may see the green gradually draw in towards the central stem, and the brown papery borders widen, just as if something were squeezing and crowding the pulp of the leaf, inch by inch, back through the leaf stem into the twig. The last traces of green linger along the sides of the veins, and before it falls, even these leaf channels will be drained dry.
When the leaves of a sugar maple give up their pulp there are wonderful changes inside each leaf. A yellow liquid fills the cells where the green pulp used to be. Chemical changes in the mineral substances deposited in the leaf cells produce wonderful shades of red and yellow, which glow where once the leaf was solid green. Iron is one of the minerals brought up in the soil water, left in the leaf, and changed to produce the bright red when the leaf mask of green is taken away.
The scarlet maple remembers its name in the autumn days. It puts on a cloak more brilliant perhaps than the sugar maple, which has a good deal of orange as well as red in its autumn foliage. The scarlet oak is amazingly brilliant; so is the sassafras and the sweet gum. The tupelo, or sour gum, also called the pepperidge, has foliage that is splashed and streaked with various shades of red and yellow. Each little leaf is so brilliantly polished that the tree’s beauty and colour seem to be doubled by reflection. The sumachs of the roadside thickets wear foliage of scarlet, each leaf drooping away from the fruit pyramid which rises, a deeper crimson, on the end of each upright shoot. The foliage and the fruit together make a colour harmony that is dazzling, indeed.
In contrast with its umbrellas of red leaves are the scarlet berry clusters of the flowering dogwood. This tree has the habit of snuggling up against the trunk of large forest trees and reaching its white flowery arms out to us in spring. How wonderful they are, on the edge of the woods, with the green leaves of the larger trees making a background for their flowers! In the autumn the same surprise awaits us, when under a towering tree with yellow or russet foliage, the dogwood leaps up like a scarlet flame, against its dark background, holding straight out its platformed branches of red leaves, tipped with berries, like rubies, set on the upturned twigs.
Often the trees are stripped by birds before the berries are ripe. It is in woods where the trees are numerous that we shall find the fruit reaching its perfection of ripeness and colour.
Among the trees that turn to purple in the autumn we may name the white oak and the ashes. Many oaks turn from green to russet, without showing any red or yellow. The lindens and the tulip trees and the beeches turn yellow; so do the poplars and willows, the hickories, and walnuts. Up and down the street you may see the yellow crowns of the silver and the Norway maples, and on the lawns the white birches have also turned to gold. The deepest red is on the black and red oaks. The brightest red is on the scarlet oak.
The flowering dogwood covers its bare branches with blossoms in May
Flowering dogwood, in flower and fruit, the winter flower buds and alligator-skin bark
It is not fair to charge Jack Frost with all the gay colours of the autumn woods. Perhaps I should say, rather, that he does not deserve all the credit people give him for painting the landscape with the sunset glories of the dying leaves. The cause is the ripening of the leaves themselves, as I have already explained. Frost may hasten the process, but if a heavy freeze comes in September, before the leaves have coloured, we lose our chance for autumn colouring that year. The leaves drop as if scalded, and the trees lose their leaf pulp, which they had expected to withdraw and save for future use. A long dry autumn of warm days and mildly frosty nights produces the finest succession of colours.
Countries that have a more moist, warm climate than ours, do not have the vivid autumn colours that we enjoy. England, and the countries of Western Europe, are like our West coast in lacking the colour changes that make October for us the most glorious month of the year. Our New England woodlands and the forests of Canada are matched in brilliancy by the wooded slopes of the Swiss Alps, and the forests along the Rhine and the Danube. In our Southern states there is little or no change that comes to the foliage towards the end of the year. The leaves on the trees of Florida are lazy in falling. They wait until pushed off by the swelling buds in early spring. Many trees that shed their leaves promptly each autumn in the Northern states, gradually become evergreen in the Southern parts of their range. The longer a tree carries its leaves, the more battered and worn they become. A tree with fresh, new leaves mingling with old ones is not a pleasant object, at least to Northern eyes. This is the way most trees in the South look in spring.
If we should travel the world over, and see the trees of many lands, in spring, in summer, in autumn, and in winter, I believe we should all come back to the clean, beautiful mixed woods of our north temperate zone, and declare that these woods are the most beautiful in the world. In the dead of winter, they are budded full of promise. We learn to love them as well in this period of rest as we do in the beauty of their spring flowers, or in the glory of their autumn colouring, or in the steady growth of summer.
Each leaf is nurse to a bud that is growing between its base and the twig. Find these little buds on any tree with broad leaves. A part of all the food that passes that way stops to feed this growing bud; and in the late summer the twig provides for the future welfare of all its buds. The thrifty tree withdraws the green pulp from its leaves, before it lets them fall. A store of starch is put away in the twig, close to each bud. This is the food supply which will be used in the spring to enable the bud to open and spread its young leaves, or its flowers, in a surprisingly short time.
When the worn-out leaf has been drained of all of its pulp, the tree lets it go. It has done its work, and given up its pulp to be stored in the twig for future use. It seems as if the tree knows that, with the coming of cooler weather, growth must stop; that the tender leaves must die when frost overtakes them. So it is a frugal habit to save all of the good green leaf pulp, and to cast off only the dry leaf skin.