You know what becomes of them. They change into a great many substances. The little particles in them let go of each other and unite with other particles. In this way gases are made which go out into the air, but some parts are solid minerals which the roots took out of the earth to build the frame of the leaves. All these minerals fall back into the earth for the roots to use again next year. So you see the leaf frame simply changes back again into the gases and minerals of which it had been made by the leaves and the roots. As the protoplasm withdraws from the leaves of the rose bushes and of many other plants, particularly the trees, the resting time of the plant is announced by the most brilliant colors, the result of certain changes going on within the leaf. These bright colors that make our autumn woods so entrancing are not dependent upon the frost, as many think, but upon certain changes going on within the leaf itself as it ripens, just as fruit, when it ripens, takes on glowing colors. The bright autumn leaves are ripe leaves getting ready to fall. Why do you suppose leaves fall? It is better that they should; the sooner they fall, the sooner they will be converted into leaf mould to feed other plants. So the plants have a way of gathering their ripe harvest of leaves. The falling of the leaf is not an accident, nor is it dependent upon the wind; when the time comes, the leaves go down, wind or no wind, though doubtless the wind helps them. When they are fully ripe, the leaves let go! The cells that connect the leaf stem with the branch shrivel and shrink until the leaf is entirely separated from the parent plant; when this happens, the leaf falls. The ripe leaf is less juicy than the young leaf; its juices have departed and left the stiff, lifeless framework and the hardened skin, with the emptied cells beneath, to find their way to the earth. But while the trees and bushes, the bulbs and underground stems store away the living part of the plant, what about the morning-glories and nasturtiums? They do not send their living part into roots or stems, for they do not grow again another year. What now becomes of them? They die, you say. I do not say that. I say they change. Of course the seeds live on. The morning-glory seeds, and the seeds of all the plants that grow wild in a climate like ours, are not hurt by the cold. You very well know that some of the life of the plant is folded up in the seeds. But the vines and leaves seem to be hurt by the cold. They fall limp to the ground. They change. The little particles of which they are made let go of each other; they unite with other particles in new ways. They float off in the air as gases. These gases are carried about by the wind and meet new plants, which build them into their leaves and stems.