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.
[Illustration: The flowering dogwood covers its bare branches with
blossoms in May]
[Illustration: 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.