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 so. How strange it is to think of the sharp thorns on a rose-bush as being made from the same sap that makes the soft, and smooth, and beautiful leaves of the roses!