THE FALL OF THE LEAVES.
It is November, and the glory of the woods is departed. Dull browns and purples show where oaks still hold their leaves. Beech trees in sheltered places are still dressed in pale yellow. The elfin flowers of the witch hazel shine like threads of gold against the dull leaves that still cling. The trees lapse into their winter sleep.
Last week a strange thing happened. The wind tore the red robes from our swamp maples and sassafras and scattered them in tatters over the lawn. But the horse chestnut, decked out in yellow and green, lost scarcely a leaf. Three days later, in the hush of early morning, when there was not a whiff of a breeze perceptible, the signal, "Let go!" came, and with one accord the leaves of the horse-chestnut fell. In an hour the tree stood knee deep in a stack of yellow leaves; the few that still clung had con siderable traces of green in them. Gradually these are dropping, and the shining buds remain as a pledge that the summer story just ended will be told again next year.
Perhaps such a sight is more impressive if one realizes the vast importance of the work the leaves of a summer ac complish for the tree before their surrender.
The shedding of leaves is a habit broad-leaved trees have learned by experience in contact with cold winters. The swamp magnolia is a beautiful evergreen tree in Florida. In Virginia the leaves shrivel, but they cling throughout the season. In New Jersey and north as far as Glouces ter, where the tree occurs sparingly, it is frankly deciduous. Certain oaks in the Northern states have a stubborn way of clinging to their dead leaves all winter. Farther south some of these species grow and their leaves do not die in fall, but are practically evergreen, lasting till next year's shoots push them off. The same gradual change in habit is seen as a species is followed up a mountain side.
The horse-chestnut will serve as a type of deciduous trees. Its leaves are large, and they write out, as if in capital letters, the story of the fall of the leaf. It is a serial, whose chapters run from July until November. The tree anticipates the coming of winter. Its buds are well formed by midsummer. Even then signs of preparation for the leaf fall appear. A line around the base of the leaf stem indicates where the break will be. Corky cells form on each side of this joint, replacing tissues which in the growing season can be parted only by breaking or tearing them forcibly. A clean-cut zone of separation weakens the
hold of the leaf upon its twig, and when the moment arrives the lightest breath of wind—even the weight of the with ered leaf itself—causes the natural separation. And the leaflets simultaneously fall away from their common pet iole.
There r re more important things happening in leaves in late summer than the formation of corky cells. The plump green blades are full of valuable substance that the tree can ill afford to spare. In fact, a leaf is a layer of the precious cambium spread out on a framework of veins and covered with a delicate, transparent skin—a sort of etherealized bark. What a vast quantity of leaf pulp is in the foliage of a large tree! As summer wanes, and the upward tide of sap begins to fail, starch making in the leaf laboratories declines pro portionately. Usually before midsummer the fresh green is dimmed. Dust and heat and insect injuries impair the leaf's capacity for work. The thrifty tree undertakes to withdraw the leaf pulp before winter comes.
But how? It is not a simple process nor is it fully understood. The tubes that carried the products of the laboratory away are bound up with the fibres of the leaf's skeleton. Through the transparent leaf wall the migration of the pulp may be watched. It leaves the margins and the net veins, and settles around the ribs and mid vein, exactly as we should expect. Dried and shrivelled horse-chestnut leaves are still able to show various stages in this marvellous retreat of the cambium. If moisture fails, the leaf bears some of its green substance with it to the earth. The "breaking down of the chlorophyll" is a chemical change that at tends the ripening of a leaf. (Leaf ripening is as natural as the ripening of fruit.) The waxy granules disintegrate, and a yellow liquid shows its colors through the delicate leaf walls. Now other pigments, some curtained from view by the chlorophyll, others the products of decom position, show themselves. Iron and other minerals the sap brought from the soil contribute reds and yellows and purples to the color scheme. As drainage proceeds, with the chemical changes that accompany it, the pageant of autumn colors passes over the woodlands. No weed or grass stem but joins in the carnival of the year.