Some plants will twine and climb in hot weather, and stand up straight alone in cool weather. This shows that in hot weather they grow so fast that they cannot hold themselves up. When it is cool, they grow slowly, and make more strong fibre. But we must leave the stem motions of plants and speak of the motion of other parts. Let me tell you how to try the leaf motion of plants. Take a house plant to try, as that is where wind will not move the leaf. Get a piece of glass about four or five inches square. Smoke it very black. Lay it under the leaf, so that the point of the leaf bent down will be half an inch from the glass. Then take a bristle from a brush and put it in the tip of the leaf. Run the bristle in the leaf so that the end will come beyond the leaf, and just touch the glass. Leave it a night and a day. Then you will find the story of the leaf’s travels written on the glass. As the leaf moves, the bristle will write little lines in the black on the glass. Try it. As you have proved the motion of the leaf with your smoked glass, let us look at leaf motion. There is, first, that motion which unfolds or unrolls the leaf from the bud. That is made because, by feeding, the plant is growing larger, and the leaf needs more room. The leaf often has, after it is grown, a motion of opening and shutting. Other leaves have a motion of rising and falling. But of these motions I will tell you in another lesson. Flowers have, first, the motion by which the flower-bud unfolds to the full, open blossom. That, as the leaf-bud motion, comes from growing. Did you ever watch a rose-bud, or a lily-bud, unfold? Then the flowers of many plants have a motion of opening and shutting each day. I shall tell you of that, also, in another lesson. Besides these motions in plants, there are others. Did you ever see how a plant will turn, or bend, to grow away from a stone, or something, that is in its way? If you watch with care the root of one of your bean-seeds, you will see that it grows in little curves, now this way, now that. It grows so, even when it grows in water, or in air, where nothing touches it. People who study these changes tell us that the whole plant, as it grows, has a turning motion. In this motion all the plant, and all its parts, move around as they grow. The curious reasons for this motion of plants, you must learn when you are older. I can now tell you only a little about it. I will tell you that the plant moves, because the little cells in it grow in a one-sided way. Thus the air, light, heat, moisture, cause the cells on one side of the plant to grow larger than the others. Then the plant stoops, or is pulled over, that way. It is bent over by the weight. Then that side is hidden, and the other side has more light, heat, and wet. And as the cells grow, it stoops that way.