Now, you know, when the plants pull carbon dioxide to pieces, they keep the carbon and return the oxygen to the air. In this way we get it to breathe. But there is more than this to the matter in hand. We are all the time breathing out carbon dioxide as an impurity; so are all the millions upon millions of animals in the world. The air might in time contain enough carbon dioxide to kill us if there were not some way of getting rid of it. You know what that way is. The plants use it up. So by giving oxygen into the air and taking out carbon dioxide, the plants keep the air fit for us and all animals to breathe. [Illustration: [Flower]] But there is more than this we have to thank them for. They shade the earth and regulate the rainfall and the water supply. Where forests grow there are always streams of water, and the large water courses are kept full the year round. The Mississippi River depends upon the far-away forests for its broad stream. The spreading crowns of the trees shade the earth and prevent the water which falls as rain or dew from evaporating rapidly. It collects into streams and flows through the land, keeping the earth fresh and beautiful. 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.