4 8 THE GARDEN OF THE WORLD 
The arrangement is something like the water 
pipes in a house. The water comes in at the 
basement, is brought upstairs through large 
pipes, and is passed on to many small pipes so 
that we may draw the water out of the faucets 
in several different rooms. 
The next thing the leaf needs is carbon 
dioxide. Carbon dioxide is very familiar to 
you, although you may not know it by name. 
When you breathe you must have oxygen, but 
the air you breathe out is carbon dioxide. It is 
not good for human beings, and if there is too 
much in the room it makes us sick. That is 
why we need to have our windows opened and 
why we say, “We must have some fresh air.” 
A plant, however, is just the opposite from 
people for it breathes in carbon dioxide and 
breathes out oxygen. A leaf breathes through 
little holes on the under side of its surface. You 
cannot see them without a microscope. 
A green leaf has the ability to take this water 
and carbon dioxide and put them together. The 
result is sugar, because sugar is made of carbon, 
