CHAPTER XXXI THE WORLD OF PLANTS 296. How Do Plants Live? Have you ever thought what a wonderful world the world of plants is, and wished you could know more of the ways in which plants live and grow? It is not easy for us to realize what a multitude of plants there are. There are the wild plants that cover almost the whole earth; there are also cultivated plants, which man cares for and protects, so that they may give him food, clothing, and shelter. There are shy wood plants so frail that to touch them is almost to destroy them; there are oaks and pines, which stand the storms of centuries, and are our symbol of strength and endurance. Then, too, there are plants so simple that they are made of but a single cell, like the green stain on the north side of fences and trees (see Fig. 228); and there are plants having such FIG. 228. The Pleurococcus is a one-celled plant; it is so small that it must be magnified many times to look as large as in the figure. Some cells are dividing, to form two cells each. complex organs as the flower of a daisy, or the insectcatching apparatus of a sundew (see Fig. 229) or a Venus's flytrap. Have you ever seen either of these plants? Botany, the science of plants, is one of the most interesting of the sciences, and farming is really a great * experiment of man and nature, carried on from year to year, to find out how perfect and abundant a crop of cultivated plants can be raised upon a certain piece of land. 66 Plants must have food and water. We recognize the need of water when we water" our garden plants, or the grass of the lawn, in dry weather; but we do not always think of the need of a plant's having food. The plant must have the different sorts of food, just like man and other animals (see § 188). It needs this food to get the energy for doing its work, to get the materials for making growth, and to repair the tissues which wear out. But there is this difference between animals on the one hand, and plants on the other: plants are able to take their food directly from the soil and the air, while animals are not, but depend on the food which plants have prepared. Is it not wonderful that plants are able to take up water, minerals, decaying vegetable and animal matter, and gases of the air, and out of these to make the delicate and beautiful structures we see and the nutritious food we eat? How does the plant do this work? We know something about the process, but by no means all; it still remains one of nature's mys FIG. 229. The sundew is a swamp plant with peculiar projecting spines on its leaves. If a small insect alights upon the leaf, the spines surround it and crush it, so that the plant may extract nutriment from its body. teries. As we have already learned, about 10 of the chemical elements are needed for plant growth (see § 157). 297. What Parts Has a Plant? What are the parts, or organs, of one of our common plants? They are the root, stem, leaves, flower, and seeds, are they not? As we think of a plant and of the things it does, we see that a plant's organs are all for one of two uses. In the first place, the plant must live, and to live it must have food. Those organs which enable the plant to get and to digest food are the organs of nutrition. In the second place, if any special kind of plant is to survive, there must be some way of starting new plants like it. Those organs which provide for the forming of young plants are called organs of reproduction. If plants are to live and flourish, both of these plant duties, nutrition and reproduction, must be carried out well. To carry them out well the plant must be fitted for the place in which it lives. Do we expect water lilies to grow in the soil of our garden, as a rose does? Then, too, if a plant is to live, the food it needs must be in the soil in which it grows, and the plant must have the right temperature, air, water, and sunlight. Name some plants that like sunlight, and some that like shady places. Some that live in water, some that prefer a fairly dry soil, and some that live and thrive in a very dry (arid) soil. Name some that grow only under tropical conditions, and some that like a cold climate. Can you name some plants which are not green? 298. How Do Seeds Begin Growing? - How can we learn the way in which a plant begins its life? One method is to grow a young plant indoors (see Fig. 230), so that you can watch all the wonderful things it does. Place a few large garden beans in lukewarm (not hot) water overnight, and look at them in the morning. You FIG. 230.- Scarlet runner beans growing. Note how the stems curve in order to get up to the light. will find that they have swollen. What entered into the bean to make it swell? How did it get in? The bean has a tough outer covering; remove it from one of the soaked beans, and you will find inside the two halves" of the bean. Is this all? If you separate the halves carefully, you will find a tiny bean-plant between them; this is called the germ, or embryo, of the bean. The process by which a germ grows into an independent plant, which can take up its own food and live by itself, is called germination, or sprouting. Plant some of the soaked beans in a box of good earth, and add enough water from day to day to keep the earth moist, but not soggy. Put the box where it will get the best sunlight. In a few days you will see that the germ has begun growing. It pushes up a crooked 'stem," which raises the dirt, straightens itself, and finally lifts the two halves of the bean into the air. The two halves are called cotyledons (kot'i-lē'dons). Between them you can now see two tiny leaves. Under the ground the stem pushes downward, and develops roots. The plant may now be called a seedling. It is able to care for itself. After a while the cotyledons turn green; finally they fall off. Their work is done; the young plant has used all their stored-up food. The bean plant continues growing by adding two leaves at a time, always at the growing tip, while the roots spread out in the ground. Plant some other seeds, such as squash seeds, lima beans, castor beans, peas, and corn, at the same time you plant the bean, and compare their growth with that of the bean. 299. What are Leaves Like? You must have noticed what different shapes the leaves of different plants have. Their edges and veining are also different; so are their thickness, the feel of their surfaces, and their shade of green. Collect as many kinds of leaves as you can, and compare them (see Fig. 231). Some leaves are broad, like FIG. 231. Leaves of the lilac, sycamore, and wild lily-of-the-valley. Which is which? Tell the kind of veining in each. those of the maple and elephant's-ear; some are moderately narrow, like those of grass and sumach; while some are very narrow and thick, like the needles of spruce, pine, and fir. Some leaves, like those of the elm, have small, saw-toothed edges; others, like the maple, are |