More than this,—large forests cause the rain to fall and the dew to collect. Their leaves condense the moisture in the air and cause it to fall as rain or be deposited as dew.
When people recklessly cut down the forests in a country, the water courses dry up, and even the largest rivers are affected.
When the spring rains fall over a country whose trees have been cut away, the water rushes down the little streams all at once and causes a terrific flood in the large rivers. It soon drains away; then the rivers fall lower and lower until they nearly dry up. This state of affairs is a great calamity, because the people can no longer raise crops on the land near where the old forests stood, for it is parched and dry months at a time.
Moreover, boats laden with coal and grain and all sorts of things can no longer pass up and down the rivers, because the water is too low.
People ought to think of these things and not destroy too much forest land. After awhile we shall have to go to work and plant trees instead of cutting them down or burning them; but it takes a long time for trees to grow, and a wiser way would be for us to take care of those we have.
You have heard a great deal about plants eating and the good they do us by eating the carbon dioxide in the air. They take this in through their leaves, and you remember they take in all their other food materials—water, nitrogen compounds, sodium, potassium, magnesium, and many other substances—through their roots.
But they do more than eat; they also breathe.
They breathe everywhere over the surface of their bodies where there are stomata or where the skin is not too thick for the air to penetrate it.
And I must tell you they breathe just as we do,—that is, they take in air, use the oxygen, and give off the carbon dioxide.
It seems rather inconsistent of them to take in carbon dioxide as food and throw it off as a waste at the same time, but that does not trouble them; they do not care whether they are consistent or not. And it is true they take in carbon dioxide and give off oxygen, and take in oxygen (in the air) and give off carbon dioxide, in one breath as it were.