Food and Fuel are the Result of Life. Fuels and foods are also alike in another respect; and that is, that, no matter how much they may differ in appearance and form, they are practically _all the result of life_. This is clear enough as regards our foods, which are usually the seeds, fruits, and leaves of plants, and the flesh of animals. It is also true of the cord-wood and logs that we burn in our stoves and fireplaces. But what of coal and gasoline? They are minerals, and they come, as we know, out of the depths of the earth. Yet they too are the product of life; for the layers of coal, which lie sixty, eighty, one hundred and fifty feet below the surface of the earth, are the fossilized remains of great forests and jungles, which were buried millions of years ago, and whose leaves and branches and trunks have been pressed and baked into coal. Gasoline comes from coal oil, or petroleum, and is simply the "juice" which was squeezed out of these layers of trees and ferns while they were being crushed and pressed into coal. How the Sun is Turned into Energy by Plants and Animals. Where did the flowers and fruits and leaves that we now see, and the trees and ferns that grew millions of years ago, get this power, part of which made them grow and part of which was stored away in their leaves and branches and seeds? From the one place that is the source of all the force and energy and power in this world, the sun. That is why plants will, as you know, flourish and grow strong and green only in the sunlight, and why they wilt and turn pale in the dark. When the plant grows, it is simply sucking up through the green stuff (_chlorophyll_) in its leaves the heat and light of the sun and turning it to its own uses. Then this sunlight, which has been absorbed by plants and built up into their leaves, branches, and fruits, and stored away in them as energy or power, is eaten by animals; and they in turn use it to grow and move about with. Plants can use this sun-power only to grow with and to carry out a few very limited movements, such as turning to face the sun, reaching over toward the light, and so on. But animals, taking this power at second-hand from plants by eating their leaves or fruits, can use it not merely to grow with, but also to run, to fight, to climb, to cry out, and to carry out all those movements and processes which we call life. Plants, on the other hand, are quite independent of animals; for they can take up, or drink, this sun-power directly, with the addition of water from the soil sucked up through their roots, and certain salts[1] melted in it. Plants can live, as we say, upon non-living foods. But animals must take their supply of sun-power at second-hand by eating the leaves and the fruits and the seeds of plants; or at third-hand by eating other animals. [Illustration: WHERE SUN-POWER IS MADE INTO FOOD FOR US]