Questions.—What is the difference between stalks and trunks? Why does a tree need so strong a trunk? Why do the stalks of plants have no wood in them? What is said of the flinty earth that is in some of them? In what ways is the flint in straws of use? What is said of the scouring-rush? How does flint get into any plant? Why does it not go into the kernels of grain as well as into the stalks? What becomes of stalks that are not woody in the winter? What is said of the woody stalks of shrubs? What are vines? How is the bean-vine supported? Tell about tendrils. What is said of the thunbergia? Describe the way in which the trumpet-creeper is supported.
CHAPTER XXVII.
THE BARK OF TREES AND SHRUBS.
In the trunk of a tree or the stalk of a shrub there are three parts. They are the bark, the wood, and the pith.
The outer bark of a tree its coat.
The bark is not all one thing. It is made up of two parts; or rather, we should say, there are two barks. There is an outer bark and an inner one. The outer bark has no life in it. It is this outer bark that gives such a roughness to the trunks of some trees, as the elm and the oak. In the birch, you can peel off this bark in strips right around the trunk of the tree. Indians make very pretty boxes of these strips of birch-bark.
The outer bark is a coat for the tree. It covers up the living parts so that they shall not be injured. It does for the tree what our clothes do for our bodies. It is not a perfectly tight coat. It has little openings every where in it. It would be bad for the tree to have this coat on it tight, just as it would be bad for our bodies to have an India-rubber covering close to the skin.
This outer bark is a great protection to the tree through the cold winter. It keeps the cold from killing the trunk and the branches. This coat of the tree covers it all, even out to the end of the smallest twig. The tree looks as if it was dead in winter without its green leaves. But there is life locked up there, just as I told you there is in the seed that is kept through the winter. The life in the tree is asleep as it is in the seed. It is ready to be waked up when the warm weather of the spring shall come. During this winter’s sleep of the tree, the living inner bark and wood are safe, covered up by the tree’s rough coat.
The inner bark.
If you peel off the outer bark, as you can very easily in the birch, you come to the fresh and juicy inner bark. This I have told you is alive. It is full of sap. It has a great deal to do with the growth of the tree. It is by this bark that the wood inside of it is made.
Trees sometimes covered with straw in winter.
You have sometimes seen small trees covered in the winter with straw tied nicely all around them. This is because they are tender trees that are not used to our cold weather. They belong to a warmer climate, and God gave them just such a coat as they needed there. And when we undertake to have such trees here at the north, the coat that God has given them is not enough to keep them from freezing in our long, cold winters. So we have to put another coat over it.
Questions.—What are the parts of the trunk of a tree? Tell about the bark. What is the outside bark for? How much of the tree does it cover and protect? What is said of the life asleep in the trees in the winter? What is said of the inner bark? Why is straw tied around some trees in winter?
CHAPTER XXVIII.
THE WOOD IN TREES AND SHRUBS.
How wood is made.
Perhaps it seemed strange to you when I said in the last chapter that bark makes wood. But so it is. Every year the living inner bark goes to work and makes a layer of wood out of the sap that is in it. This work is done in the warm weather. In the winter there is no wood made. The tree is asleep then.
It is what the bark does that makes the tree larger every year. A new layer of wood is formed by it all up the trunk, and along out to the end of all the branches.
Its layers.
The different layers of wood made in the different years are often very distinct from each other. You can see them in a log that has been cut or sawn across. Sometimes they are so distinct that you can count them, and so tell just how many years old the tree is. Here is a representation of the sawn end of the trunk of a tree. You see that the rings of the wood are very plain.
Pipes in the wood for the sap.
The wood part of the trunk and branches is full of small pipes. It is through these pipes that the sap goes up from the roots and gets to the leaves. It is in this way that it goes to the very ends of the topmost boughs of the tallest trees. This is very wonderful. How the sap is made to go up such a great distance through these pipes in the wood we do not know. There is only one way that man can make water go so high through pipes. He can do it by a forcing-pump. But we can see nothing like forcing-pumps in the trees. We find nothing but these pipes going from the roots up to the leaves. And the sap is flowing up through them very quietly all the time.
Sap-pipes numerous.
In a large tree there is a multitude of these pipes in the wood. And when you look at the huge trunk, think what a quantity of sap there is going up through it all the time to keep all those leaves fresh and green. If you could see it all in one pipe it would be quite a stream.
Heart-wood.
If you look at the end of a log you will see that there are two kinds of wood. The wood in the centre is different from that which is around it. It is called the heart-wood. The pipes in it are stopped up, and no sap can go up through it. The pipes for the sap are clear only in the newest part of the wood.
Pith.
The use of the pith of trees and plants we do not understand. The pith is very small in trees, but it is quite large in some plants and shrubs. All boys know that it is very large in the elder. It is also large in the stalks of corn, and of the sugar-cane.
Questions.—How is the wood in a tree made? What is said of the different layers of wood? What is said of the small pipes in the wood? Do we know how the sap is made to go up in them? What is said of the quantity of sap that goes up in the trunk of a large tree? What is said of the two kinds of wood that you see in looking at the end of a log? What do we know about the pith of trees and plants?
CHAPTER XXIX.
WHAT IS MADE FROM SAP.
Every thing that you see in a tree or a plant is made from the sap. The bark, the wood, the leaves, the flowers, the fruit, are all made from it. Even the root that sucks up the sap from the ground is made from the sap itself.
The great difference in things made from sap.
It is strange that so many different things can be made out of the same thing. It is strange that a rough bark and hard wood can be made from the same thing as the beautiful flower and the delicious fruit. Look at an apple-blossom, and then look at the bark of the tree, and think of them as being made from the same sap. You can hardly believe that it is