The Work Done by Leaves
The leaves want a great deal of sunshine and air, for they are busy all day long, making food. Have you ever thought how wonderful it is that plants can make their own food? You do not make your food, and no animals make their own food. All you eat has once been either an animal or a plant. In a cake, for instance, the flour comes from grains of wheat, the currants from a little tree, the sugar from the sugar-cane, the spices come from trees, and the candied peel from fruits.
The other things you eat are meat, fish, birds, vegetables, and fruits, and all these have once been alive.
Plants do not feed like this. Their roots take in water out of the earth, and other substances, such as lime, soda, and potash, dissolved in it. The leaves take in gases out of the air. But earth, air, and water are not living food. You or I could not live on them. The plant can.
The pretty green leaves we love so much work very hard. When the sun shines upon them they can turn the water and gases into living food, and this food makes more leaves, flowers, and fruits which we eat.
See how useful plants are! If they did not make food, there could be nothing alive in the world. Insects feed on plants, and birds feed on insects. Sheep feed on grass, and we feed on sheep. Rabbits feed on plants, and foxes and weasels feed on rabbits. If there were no plants, there could be no insects, no birds, no animals, and no men alive.
But this is not the only useful work which plants do. You know that if many people are shut up in a room, they use up the fresh air, and breathe back bad air, which is not fit to use again. Now plants want this foul air. They take it in through their leaves, and use a gas which is in it to help them to grow. So they not only turn gases into food for us to eat, but in doing this they use the bad air we send out of our mouths, and give it back to us fresh and pure. This is why it is so healthy to live in the country, where there are so many plants.
You will find it very interesting to look at the leaves of plants, and notice their shapes, and how they are arranged on their stems so as to get light and air.
I think you must know the common Dead-nettle, which is so like a stinging-nettle but does not sting. It grows in the hedges, and has a pretty purple or white flower shaped like a hood. Its leaves are arranged in pairs all up the stem, and each pair stands exactly across the pair below it, so as to let in plenty of light.
The glossy green leaves of the ivy on the wall lie out flat, and have long stalks, so that they can stand out well into the air.
The leaves of the Nasturtiums in our gardens are shaped like a round shield. The leaf-stalk grows from under the middle of the leaf and is very long. So the leaf looks up straight to the sky, and gets plenty of light and air.
The leaf of the Horse Chestnut tree is divided into leaflets, so that it looks as if it were made of five leaves, and each leaflet is spread out to the light.
The leaves of the little Wood Sorrel, which children love to bite because it tastes sour, have three round leaflets like the Shamrock, and these leaflets droop down at night, or on a wet day, but stand up wide open when the sun is shining.
And now let us go back to our shepherd's purse. We have not yet looked for the flowers; they grow on stalks which come out between the leaf-stalks and the stem. On these stalks there are some smaller leaves and a good many seed-pods.
Above the seed-pods at the top of the stalk are some white flowers growing close together. They are so small that you can scarcely see the parts. But you can make out that they have four outer green leaves and four white inner leaves. In the next lesson we will learn more about these.
Gather six plants with different shaped leaves and notice how they grow upon the stem.