Leaves are of different shapes because they belong to different families of plants or trees. They are a good deal like people in this respect. Hardly two people in the world look exactly alike, but there is a distinct family resemblance in members of the same family. It is difficult to say just what happens inside the tree to determine the shape of the leaf and that causes them to possess different shapes from others. The shape of the leaf is a mark of identification of the family to which the tree or plant belongs, just as you can tell from a dog’s ears and from other characteristics what his breeding has been. In the case of plants and trees however it is quite probable that the shape and texture of the leaves has been developed as the result of the conditions under which the plant grows. A plant or tree throws off oxygen and takes in carbonic acid gas through the surface of the leaves. To thrive and be healthy it must secure just the proper amount of this food and as the quantity of food taken in depends upon the amount of surface exposed through the leaves, each particular tree or plant has developed in its own direction in this respect until this feature of their structures has been adjusted properly to their needs. It is a good deal like the radiation of heat in your home. Why Are Some Radiators Longer Than Others? When the plumber gets ready to put in the radiators in the home he figures the cubic measurements of the room and then puts in a radiator, the outside surface of whose pipes, is in the right proportion to throw off sufficient heat to fill the room or heat all the air in the room. It requires a certain number of square inches of radiator surface to heat each cubic foot of air space and a good plumber can figure this to a nicety. If he puts in a radiator however that has not sufficient number of square inches on the outside of the pipes, the room will not be heated properly. In the same way, the trees, require that their leaves have a certain amount of square inches of surface space in proportion to the size of the tree, to enable them to do what is required of them and this is arranged by nature so that the trees grow naturally, and no doubt the shape of the leaves has something to do with this. What Makes Roses Red? All roses are not red. Some are white and others pink or of still another color. The color of the rose, and in fact the color of all flowers is due to the way they absorb and reflect the sunlight. In the case of the red rose, the something in the plant that determines the color, absorbs all the other colors in the sunlight and reflects the pure red rays and that makes the color of the red rose. You cannot see the color of any flower when it is perfectly dark. That is because they have no color of their own, but only the colors which they reflect when in the sunlight or some other light. The question of colors is more fully explained in another part of the book.