David Shelton, age 10, of Shreveport, La., for his question:
How do the leaves know when to fall?
The oak and the ash, the beach and the birch have tender leaves. A crisp frost will freeze the liquid sap in their veins. After one frosty night, the thin, delicate leaves of the peach and the apple shrivel up and turn black. The larch and the spruce, the pine and the fir have leaves like tough needles. The frost cannot reach the sap through their waxy coats. The trees with delicate leaves shed them before winter comes and grow new leaves in the spring. Do these trees have a calendar to ' tell them the date?
Lets look further around this green world of ours, Trees are plants and in nature there are plants almost everywhere. Some need but little warmth,, some air and moisture, some soil and sunlight. But some plants need morn warmth, more air, more moisture or deeper soil than others. So we find each one of the countless plants growing in the spot best suited for it.
Tall pines climb up the snow‑clad slopes end cactuses have the desert almost to themselves. Seaweeds cling to rocky beaches and palm tress wave on tropical islands. Sunflowers and poppies soak up the sunshine and ferns spread their~feathery fronds in the shade. Does each plant choose where it will live?
No plant, of course, can solve a problem. It cannot choose where it will live or read a calendar. The fern found its shady spot by accident. Its parent spread perhaps a trillion tiny spores into the breezy air. Most of them fell in unsuitable places such as the sea and the desert. This one little spore found the spot in which it could grow.
All plants grow by fits and starts. They have a growing season and a resting season. This is true of trees, pins trees may have two or more short growing seasons during the year.
The elm and the oak have one long growing season and one long resting season during the year. In the growing season, they need lots of green leaves to make plant food. These wide, flat leaves need a lot of support from the tree. When the growing season is over, they become a burden.
Come fall, the oak and the ash get ready to dump their leaves. The chemicals in the leaves are broken up and toted away. This causes the bright colors of autumn. The sap no longer feeds the leaves. They shrivel and fall. But the tree does not plan to escape the frost. It is merely getting ready fir a long rest period.
It so happens that these trees do well in our climate, where cold winters follow warm summers. But if an acorn fell in the frozen north, it would perish like the countless unlucky fern spores.