SUNLIGHT FACTORIES 
49 
oxygen, and hydrogen. Carbon dioxide is made 
of carbon and oxygen, and water is made of 
oxygen and hydrogen. You can see that there 
will be some oxygen left over; so the leaf 
breathes this out. This sugar is what the plant 
needs for food. It is sent all over the plant 
through slender tubes. We get our sugar from 
plants that make more than they can use—the 
sugar cane and sugar beets, for example. 
The leaf can only make food when the sun 
is shining and the weather is warm. That is 
one reason why leaves drop off in autumn. 
They cannot work in winter, so the tree rests. 
The leaves do not work at night, either, because 
there is no sun. The tree must have food all 
winter, even if it isn’t working, and it must 
have some stored up to use in the spring until 
its leaf factory has a good start. Therefore the 
tree stores away some food, just as the squirrels 
store away nuts. It wouldn’t be a good idea to 
store the sugar because it dissolves in water and 
would soon be lost. Most plants have the power 
to change sugar into starch. The starch does 
