CHAPTER XX.
THE USES OF LEAVES.
Refreshing moisture from leaves.
One use of leaves, as I told you in the last chapter, is to supply the air with water. In the hot weather the air would be very dry and uncomfortable to us if the leaves did not breathe out moisture from their pores. You can see how this is if in a hot day you walk across a sandy plain where there are no leaves except those of the scanty grass and weeds. Here no moisture is breathed out upon you, to lessen the heat that you suffer from the burning sun.
Another use of the leaves is this. They are pleasant and beautiful to the sight. I have told you about this use of them in the beginning of the seventeenth chapter.
Their shade.
Another use of leaves is to give shade. We know how refreshing this is to us in a hot day. When in a city we walk through streets where there are no trees, how delightful it is to come out of the blazing sun into a square that is full of trees! How comfortable are the cows in the pasture lying under the trees at mid-day, chewing the cud!
But the shade given by leaves does good not merely to man and animals. It does good to fruits, if there is not too much of it. The sun would very often be too hot for the fruits, if it shone full on them all the time. So the leaves partly shade them.
The grape-vine stripped of its leaves.
The chief use of leaves is to keep plants and trees alive and make them grow. If you should strip off the leaves from a plant as fast as they came out, you would, after a while, kill it. Sometimes worms eat up the leaves on trees. If this is done year after year to a tree it dies. I knew a man to strip off all the leaves from a grape-vine. He thought that it would make the grapes grow finely. He had seen people take off some of the branches from grape-vines, to make the grapes grow large and full. So he thought that if he took all the leaves off, the sap would all go into the grapes and make them very large. He thought, too, that the sun would make them ripen fast. But he found that the grapes stopped growing, and wilted, and dropped off. There are two reasons for this. The sun was too hot for the grapes when all the leaves were gone. And besides, there were some leaves needed to keep the grapes alive.