WOOD.

WOOD is composed of carbon, oxygen, and hydrogen, of a solid united with two gases. When we make charcoal we decompose the wood. We send the oxygen

and hydrogen into the air by heat, and the carbon is left.

Though wood can be thus decomposed,1 you cannot take the ingredients and unite them so as to make wood. If powdered charcoal be mixed with water, there are the ingredients of wood together; but you cannot make them unite to form wood.

Although we cannot make the ingredients of wood unite to form wood, it is done in the tree. Let us see how. Much of the carbon is furnished from the air, being taken in by the leaves, as you learned on page 291. Then the water coming in the sap from the roots furnished oxygen and hydrogen; for water, you know, is composed of these two gases. We may say, then, that the tree makes its own wood out of charcoal and water.

The bark of trees is wood, only in a different form from that which it covers. Hold a leaf so that light can shine through it. That delicate framework you see is a wooden framework. More than this, the skin of the leaf and its filling up are wood. The whole is wood except the sap, and that which gives it its beautiful colour; and what I have said of leaves is true also of flowers. The most delicate flower you can find is made of wood-very, very fine and delicate is such wood, and yet it is wood.

You see a hyacinth growing in a glass vessel, in which is nothing but water. The plant is little else than wood filled in all its cells with water. See how this wood is

formed, water furnishes the oxygen and hydrogen, and the carbon comes from the air.

Every stalk of grain and grass is chiefly wood. In both cases fine particles of flint are scattered in the wood to make it firm enough to stand even a gale of wind.

Much of the clothing you wear is nothing but wood. You can hardly believe this, but so it is. A shirt, whether of cotton or linen, is a wooden shirt. Cotton or linen fibre is woody fibre. It is composed of carbon, oxygen, and hydrogen in exactly the same proportions with what we call wood.

You remember that you learned on page 300 about the old-fashioned tinder-box; charred or scorched linen was always kept in the box to catch the spark from the steel. That was really charcoal, made from linen, just as we make charcoal from wood; that is by a partial burning. It was used instead of common charcoal, because being so fine sparks readily set fire to it.

All paper is wood. When fine, as writing paper, it is made of cotton and linen rags, and these are wood. If you tear a piece of letter-paper, and look at the torn edge through a microscope, you will see very plainly the woody fibres pointing in all directions from the edge.

All the framework, as we may call it, of fruits, is wood. All the partitions in fruits are wooden partitions. The orange, you know, is divided into several parts by partitions. These are of wood. The juice of an orange is inclosed in thousands of little bottles, and these are wooden bottles. Observe and see how pretty they are, and how nicely they are packed in each part of the orange. Their large, rounded ends are towards the peel, and their slender, pointed ends are

towards the middle of the orange. When you eat an orange you crush a multitude of these wooden bottles, and the juice runs out of them, so, when you eat any juicy fruit, you break up wooden apartments or cells that hold the fluid. Even in the most juicy fruits there is wood, and the skins or coverings of fruits are made of wood.

The coverings of seeds are wooden. In nuts the woody substance forming the covering is very dense and hard, as in a cocoanut, walnut, &c.

"Easy Introduction to Chemistry.” Edited by the REV. A. RIGG.

1. DECOMPOSE, to resolve any substance into its original elements or component parts.

VEGETATION.

EVERY plant comes from a seed; and when this is put into the ground, a root shoots downward into the earth, and a stalk shoots upward into the air.

As the stalk and root are built, channels or tubes are formed along them. Through these tubes sap goes to every part of the plant. This is true of every plant, from the smallest to the largest. Look at a very large and high tree, the life in a little seed began that. It pushed up the stalk a little higher and higher, making tubes in it all the while; and now that it reaches so high, sap goes along those tubes from the very ends of the roots to the very ends of the leaves.

Let us see of what the seed, from which all this comes, is composed. It is chiefly starch and gluten. Now these substances are insoluble. Of what use, then, can they be in growth, when they cannot circulate in the

tubes. Unless they be rendered soluble, they must remain in the seed.

But the required change is produced in them. As a seed becomes moist, oxygen is absorbed, and thus gluten is made soluble, and the starch is changed into sugar, which you know is soluble. So as fast as channels are made in the upshooting plant, sap, with dissolved gluten and sugar, circulates in them. When the little root is formed, and the stalk reaches the air and puts out leaves, the seed may be said to have passed away, its gluten and starch are exhausted. The plant now gathers all its materials for growth from the soil and the air. These are carbon, oxygen, hydrogen, and some nitrogen. As you have learned, it obtains from the air carbon, taking it in at every pore in the leaves. Oxygen and hydrogen are obtained from the water that waters the roots.

From whence comes the nitrogen? All the nitrogen, which a plant gets, comes through the roots. There are various substances in the soil that supply it. One is ammonia, which is composed of nitrogen and hydrogen. This substance abounds in most manures, especially in guano.1

You see that carbon, oxygen, hydrogen, and nitrogen are the four grand ingredients in vegetables and plants, also that the first three of these compose the framework, the structure. There is no nitrogen in woody fibre, it is found only in some fruits and juices. It is put there as a part of the food of animals. Plants gather nitrogen from the earth, and deposit it within their fruits and juices for the use of man and other animals. It is deposited just where it is wanted. For example, none is lodged in the stalk of wheat, but it is in the seed or grain, so that we have it in the flour with which we make bread.

Besides these things, silica or flint is in the stalks of grain and spires of grass. In many vegetables, as mustard and onion, there is sulphur. Then there are phosphorus, lime, potash, iron, &c. in the sap through the channels of the first part of this chapter.

All these are carried which I told you in

Now think what sap is. It is chiefly water, having dissolved in it the various substances already mentioned. Water, then, not only furnishes the plant with oxygen and hydrogen, but is the means by which other substances, needed by the plant, are carried in its channels or tubes to the very ends of the leaves. Some of the water remains in the plant, giving its oxygen and hydrogen to it, to help to form wood, starch, gluten, sugar, &c. But the largest part of it is breathed into the air through the little pores of the leaves.

Some

The quantity of water that passes from the roots through the channels in plants is much greater than most people suppose. We can get some idea of this by ascertaining how much passes from the leaves. experiments have been tried in regard to this, and it was found that a single cabbage breathed from its leaves into the air, in the course of twenty-four hours, nearly a quart of water. If so much comes from a cabbage, how much must all the leaves of a huge tree throw out into the air!

In all juicy fruits there is much water. In the water-melon there is so much that it gives its name to the fruit. It is almost all water, with a little sugar dissolved in it. The cells containing this juice are really wood, but very delicate, even more so than those of the orange.

It is the water in leaves and flowers that gives them softness. You know how stiff the leaves of flowers are