These seeds are winged in order that they may be blown abroad on the wind and plant new forests farther afield. If they all dropped close under the shade of the parent tree few would live beyond a year or two.
Where the wing-like husks come together there is a thickening of the base of each into an ear-like lobe, holding a seed. The wrapping of this seed softens, the seed enlarges as the embryo within it grows, the husk is pushed open, and slowly comes forth the baby tree, composed of two leaves and a stem. These two leaves, although very small, are perfect and even green in the unopened seed.
They are soft and fleshy; in fact, they are pantries, full of food, ready for the weak little plant to feed upon until it is strong enough to forage and digest for itself. Everyone knows that babies must be carefully fed on delicate food until they get their teeth. The baby plant also needs well-prepared food.
Between the two leaves is a little white stem. The two leaves unfold, and in a few days the air and sun have made them bright green. The stem between them thrusts a little root into the earth; this root is furnished with hairs. When the root is well-formed and the two seeds have reached full size, a bud has formed in the axil between them.
This is the growing point of the new tree. This bud presently opens into a pair of well-formed maple leaves.
As these leaves increase the seed-leaves diminish; the plant is feeding upon them. The ascending stem presses its first pair of leaves upward, forms between them two more, and then two more, and thus on.
Small branches are formed by the end of summer, the seed-leaves are exhausted, and the plant is doing its own work.
Under the trees in March we find many interesting examples of seed-growth. The feeding or seed-leaves of the young plant are called cotyledons. All flowering plants have cotyledons; the plants whose leaves have dividing or radiate veins, and whose stems are woody, or, at least, not hollow, have two cotyledons; grasses, reeds, corn, and other grains, lilies, bamboos, all plants with hollow stems and the leaf-veins parallel have one cotyledon, while pines and trees of their class have from three to twelve cotyledons, always set in a circle.
The seeds, the new plants, or seedlings of any variety are very numerous. This is needful, as they are subject to many disasters. They may be eaten by animals or birds, withered by too great dry heat, devoured by worms, frozen or ruined by overmuch shade. If plantlets were not very numerous the varieties of plants would presently die out.
When the March winds shake out the leaf-buds and the seeds in the ground begin to stir with strong life, we are led to think of the plant’s host of enemies.