LESSON XI.
AIR, WATER, AND SAND PLANTS.
Most of the plants which you see about you grow in earth or soil. You have heard your father say that the grass in some fields was scanty because the soil was poor. You have been told that wheat and corn would not grow in some other field, because the soil was not rich enough.
You understand that. The plant needs good soil, made up of many kinds of matter. These minerals are the plant’s food. Perhaps you have helped your mother bring rich earth from the forest, to put about her plants.
But beside these plants growing in good earth in the usual way, there are plants which choose quitedifferent places in which to grow. There are air-plants, water-plants, sand-plants. Have you seen all these kinds of plants?
You have, no doubt, seen plants growing in very marshy, wet places, as the rush, the iris, and the St. John’s-wort. Then, too, you have seen plants growing right in the water, as the water-lilies, yellow and white; the little green duck-weed; and the water crow-foot.
If you have been to the sea-shore, you have seen green, rich-looking plants, growing in a bank of dry sand. In the West and South, you may find fine plants growing in what seem to be drifts, or plains of clear sand.
Air-plants are less common. Let us look at them first. There are some plants which grow upon other plants and yet draw no food from the plant on which they grow. Such plants put forth roots, leaves, stems, blossoms, but all their food is drawn from the air.
I hope you may go and see some hot-house where orchids are kept. You will see there splendid plants growing on a dead branch, or some other dry thing, high up in the air.
Did you ever see a piece of mistletoe? It grows on some tree. It has nice green leaves and whiteberries. That the mistletoe draws all its food from the air has been proved. It thrives as well on a dead tree as on a live one. A Frenchman, who loved to study plants, made a mistletoe plant grow on a cannon ball. Another mistletoe sprouted and grew from a seed held out on the point of a copper needle.
Thus, you see, these air-plants gain all their food from the air.
Water-plants will seem to you to grow in a more natural way. Most of them are rooted in the earth at the bottom of the pond, or ditch, where they grow. As the blossoms form, the flower stem grows long, and the flower rises to the top of the water.
There the lovely blossom floats about in the sunshine. It is moored by its long stem to the root, as a boat is moored by a rope. When the seeds are ripe, the flower stem sinks down again. The leaf stems rise to the top of the water. There the leaves lie spread out, to breathe the air.
Now when these leaves of water-plants are made to grow to the top of the water and live, they are broad, and often shaped like a shield. They are to spread out on the surface of the water, and catch all the air and sunshine that they can.
But there are other kinds of water-plants which have their leaves growing down under the water. All these leaves made to stay in the water are fringe-like and narrow. They look like wide leaves cut into many small strips.
Most sea-weeds have fringe-like leaves. Yet there are sea-weeds with wide leaves. They, like the fish, are made to live in the water all the time.
The fresh-water plants generally mean to come to the top of the water some time. They have green leaves. Their leaves can keep green only by the action on them of the air and light. This is why the leaf is made fringe-like. Its fringed leaves act as a net, floating around in the water. These leaf-nets catch not fish, but air-bubbles, and rays of light.
The water crow-foot, or water buttercup, has two kinds of leaves. Those at the bottom of the stalk are all in fine fringes. The leaves at the top are broad, like other crow-foot leaves.
There are some water-plants which do not root at the bottom of the pond. They spend all their lives floating about. A little plant called “duck-weed” is one of them. It has a soft, green body like two halves of a tiny pea. Its roots are three or four fine threads. It gathers all its food from the water.
Most water-plants have two sets of roots. One set holds the plant fast in its place. The other roots spring from the base of the leaves. They gather food from the water.
Now, while leaves that grow in the water are fringe-like, I think you will see that leaves of plants that grow in sand must be just the opposite.
If you examine a plant growing in dry sand, you will find that it has thick, soft, juicy leaves. The leaves of sand-plants are seldom flat. They are shaped like fringes, or the palm of your hand, or like little rolls.
Why is that? Can you not guess? The roots of these sand-living plants can get very little water. Only when rain and heavy dew fall can they get moisture. If they are wise little plants, they will store moisture up.
These sand-plants store up food and moisture in their leaves. It may surprise you that plants, growing in such dry places, have leaves so full of juice. The leaves are their pantry. They are full of saved-up water.
You will notice another thing. Many of the sand-plants have their leaves covered with prickles, hooks, and thorns. The leaves are rough, like burrs. Why is that? Is it not so, that birds and beasts will not want to eat them?
If the leaves are nipped off by animals, these plants must die. Their sand home gives them no water for their roots. If the leaves are eaten, all the plant must perish.
As there is so little water in the sand to carry food to the plant through the roots, the leaves of these plants must do most of their eating. So in the sand-growing plants the leaves serve as mouth, stomach, and pantry.
By the sea-side you will find plenty of sand-growing plants. You can study them, and prove these points for yourselves.
Children who are not by the sea may, perhaps, have, near where they live, a curious sand-loving plant, the cactus. The cactus prefers a sandy soil. I have seen a large cactus, covered with yellow blooms, growing right in a drift of clear sand.
You will notice that what you call the leaves of the cactus are not real leaves, but thick, odd-shaped stems. These stems are green, and answer for leaves. They are of many queer shapes. They are covered with little clusters of prickles. As they serve for leaves, these odd stems of a sand-plant are fleshy and juicy. The plant stores its food and drink in them.