This is easy to understand in climbing plants. Their long, slim stems are weak. They bend with their own weight. They bend to the side that is slightly heavier. Their motion then serves to find them a support. As they sweep around, they touch something which will hold them up. Then they cling to it. Now, there is another reason for a tendril taking hold of anything. The skin of the tendril is very soft and fine. As it lies against a string, or stick, or branch, the touch of this object on its fine skin makes the tendril bend, or curl. It keeps on bending or curling, until it gets quite around the object which it touches. Then it still goes on bending, and so it gets around a second time, and a third, and so on. Thus the tendril makes curl after curl, as closely and evenly as you could wind a string on a stick. Some plants, as the hop, move around with the sun; other plants move in just the other direction. It is as if some turned their faces, and some their backs, to the sun. FOOTNOTES: [8] What you call the leaf of a fern is, properly speaking, a frond. LESSON X. PLANTS AND THEIR PARTNERS. Did I not tell you that the plants had taken partners and gone into business? I said that their business was seed-growing, but that the result of the business was to feed and clothe the world. In our first lessons we showed you that we get all our food, clothes, light, and fuel, first or last, from plants. “Stop! stop!” you say. “Some of us burn coal. Coal is a mineral.” Yes, coal is a mineral now, but it began by being a vegetable. All the coal-beds were once forests of trees and ferns. Ask your teacher to tell you about that. [Illustration: THE THREE PARTNERS.] If all these things which we need come from plants, we may be very glad that the plants have gone into business to make more plants. Who are these partners which we told you plants have? They are the birds and the insects. They might have a sign up, you see, “Plant, Insect & Co., General Providers for Men.” Do let us get at the truth of this matter at once! Do you remember what you read about the stamens and pistils which stand in the middle of the flower? You know the stamens carry little boxes full of pollen. The bottom of the pistil is a little case, or box, full of seed germs. You know also that the pollen must creep down through the pistils, and touch the seed germs before they can grow to be seeds. And you also know, that unless there are new seeds each year the world of plants would soon come to an end. Now you see from all this that the stamens and pistils are the chief parts of the flower. The flower can give up its calyx, or cup, and its gay petals, its color, honey, and perfume. If it keeps its stamens and pistils, it will still be a true seed-bearing flower. It is now plain that the aim of the flower must be to get that pollen-dust safely landed on the top of the pistil.