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And because leaves are so important to trees -- and, therefore, to every one of us -- and because leaves are particularly interesting in the beauty of their autumn coloring, I begin this, the fifth of our series of "Adventures in Nature's Wonderlands," with the opening of the school year in September, and with the subject of leaves and how they get their lovely colors, and why they fall, and the good the dead leaves do -- things like that. It's a most striking thing about the good citizenship of our friends the trees that, in addition to supplying us with food and shade and lumber, and shutting off the high winds and all, they more than pay "their board and keep" by handing back to the soil every fall more than they have taken out of it during the summer. For example, in what are known as the "pine barrens" in the South -- wretched soil, too poor for ordinary crops -- what is known as "Old-Field Pine" will grow of its own accord. Then, after a while, the trees can be cleared out and fine crops can be raised by drawing on the accumulation of enriched soil made by the decay of the "needles," the leaves of the Pine. This lasts for three or four years. Then, if the farmer fails to add any fertilizer himself, the land goes back to barrenness. As I said in The Adventures of a Grain of Dust, what can such a farmer expect, always drawing on his bank and never putting anything in? HOW THE TREES PAY THEIR BOARD -- AND MORE The fallen leaves, decaying, make what is called "humus," and this humus is a very important thing to have in the soil. The roots of trees continually bring up mineral salts from the subsoil, and a certain amount of these valuable salts are left behind in the leaves when they fall. The tree, having closed business in preparation for the winter, has no further use for these salts, which are merely the raw material for its thousands of little food factories, the leaves. Then, as the fallen leaves decay, these salts are carried into the surface soil by the rains and left just where they will be wanted by growing things the following year. It is for this reason that certain kinds of trees, hardy pioneers like the Old-Field Pines, can be profitably grown on soil far too poor to raise ordinary crops. The acids produced by the decay of the leaves also help to perform one of the miracles of nature -- the changing of rocks into humming-birds and trees and squirrels and wood flowers and fresh milk. These acids of decay dissolve rock; and rock, as you no doubt know, is the original substance out of which soil is made. So the trees, from year to year, are constantly "converting a liability into an asset," as a business man would say. The stones of the field, which are only a nuisance to the farmer in their raw state, are of great benefit to him when their hidden riches are unlocked -- when, by the wonderful alchemy of Nature, they are converted into soil; for the rocks contain sulphur, phosphorus, potash soda, iron, silica -- it's the silica that helps put a good backbone into the wheat blades and the corn -- and these things are converted into wood and fruit and nuts and vegetables. To this faculty which dead leaves and other dead vegetation possess of helping convert rock into soil is due the curious fact, recorded in The Adventures of a Grain of Dust, that pebbles, under certain circumstances, are good for cows. In the counties of Wisconsin where there are plenty of pebbles, the production of butter and cheese is something like 50 per cent greater than in regions where there are comparatively few pebbles. And if you examine a pebble taken from among the roots of grasses or the finer roots of trees you will see the "finger-prints" of these little roots, where their acids have eaten into the stone. |
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