LEAF GREEN AND SUNBEAM 
UT the earth broth which the roots supply is not 
the only article of importance in the plant’s bill 
of fare. 
The air about us holds one thing that every plant 
needs as food. 
This air is a mixture of several things. Just as the 
tea we drink is a mixture of tea and water, and milk 
and sugar, so the air is a mixture of oxygen and nitro- 
“gen, and water and carbonic-acid gas. 
Oxygen, nitrogen, and carbonic-acid gas, — each one 
of these three things that help to make the air is what we 
call a gas, and one of these gases is made of two things. 
Carbonic-acid gas is made of oxygen and carbon. 
Now, carbon is the food which is needed by every 
plant. But the carbon in the air is held tightly in the 
grasp of the oxygen, with which it makes the gas called 
carbonic-acid gas. 
To get possession of this carbon, the plant must 
contrive to break up the gas, and then to seize and 
keep by force the carbon. 
This seems like a rather difficult performance, does 
it not? For when a gas is made of two different 
things, you can be pretty sure that these keep a firm 
hold on each other, and that it is not altogether easy 
to tear them apart. 
Now, how does the plant meet this difficulty ? 
You cannot guess by yourselves how this is done, so 
I must tell you the whole story. 
