HOW PLANTS BREATHE 131 
is taken from the air and joins with carbon in the 
wood or in the coal, and carbon dioxid is set free. 
This joining of oxygen and carbon is called oxidation. 
In the living plant the joining of the oxygen from the 
air with the carbon in the plant takes place slowly, so 
that no flame or fire is made, but it is still oxidation. 
Oxidation takes place slowly in animals in the same 
way when they are breathing. But while the plant is 
being partly oxidized or consumed as it breathes, this 
very thing enables it to do more work, in growth 
and in other ways. When you run or play hard, you 
breathe faster. A part of your body must be oxidized 
to get power or energy to play; or to work either, for 
play is one kind of work. 
The carbon dioxid which is given off is one form of 
the waste from your body, or from the plant’s body, 
while work of this kind is going on. To take the place 
of this waste you must eat, and you know how hungry 
you are when you are growing and playing. You need 
a great deal of food to make new living materials to 
take the place of the waste, and to supply what is 
needed for growth. So it is with plants; they need 
food for growth, and to repair waste. 
