The airing of the sap.
You remember that I told you in the chapter on leaves, that they have much to do with the growth of a plant. You can now see why this is so. The sap has to go up to the leaves to be made good sap. Just what the air does to it there you are not yet old enough to understand. But after a little time you will be able to understand this, and then you will see that leaves are very properly called the lungs of plants, and that they breathe with them as we do with our lungs, though in a different manner.
The sugar made from the sugar-maple.
I have said that the sap that goes up is not of much use, and that every thing in the plant is made from the sap that goes down. This is not always so. In the sugar-maple it is the sap that goes up in the early spring that has the sugar in it. The sugar-gatherers tap the trees before the leaves are put forth. The leaves, then, have nothing to do with making the sugar. How it is made we can not understand. We suppose that it is done in the root, where the mouths are that drink up the sap from the earth. But though we do not know how it is, in some way every sugar-maple as soon as it begins to be warmed by the air of spring becomes at once a sugar-factory.
Though most of our sugar comes from the sugar-cane of southern climates, a great deal is made from the sap of the sugar-maple in some parts of the northern and western states in this country. A very busy time they have in some places in the early spring in collecting the sap and in boiling it down. The sirup is often sold as maple-sugar molasses. But more often it is made into sugar; and great quantities of it are sold every year. In some places where it is made many of the people use no other sugar.
The sap always in motion except in winter.
The sap is all the time in motion in the trees and plants in all the warmer months of the year. It is always going up and coming down. It does so till the leaves fall and the cold of winter comes. Then all this motion stops. And through the winter the sap is almost as still as if the trees and shrubs were dead. Then when the spring comes, the mouths in the roots begin again to suck up sap from the ground, and it runs up and down in the little pipes as it did the year before.
As you look at all the trees and plants about you, think how much sap there is running up and down in their pipes. Look at a very large tree, and think of this. In multitudes of pipes in that huge trunk the sap goes up to the very end of all the branches to the leaves, and then it comes down in other pipes. How wonderful this is, and yet how few there are that ever think about it!
Questions.—Where are the pipes in which the sap goes up in a tree? Where are the pipes in which it comes down? What is said about the water in the sap? What becomes of a part of this water? Why is it necessary for the sap to go up to the leaves? Are things made from the sap that goes up, or that which comes down? How is it with the sugar in the maple? Where is its sugar made? Is the sap always in motion?