156 
HOW WE -ARE HELPED BY GEA CEE 
AND SUNBEAM 
HE cell in which Leaf Green lives has no little 
mouths such as we saw in the picture some time 
ago. 
Its walls are so delicate that the carbonic-acid gas 
passes through them quite easily, —as easily as the 
gas escaping from an unlighted jet in the schoolroom 
could pass to your nose even if you wore a veil, or as 
easily as water would pass through a piece of muslin. 
But between Leaf Green’s cell and the outer air are 
other cells, —those which make up the outer covering 
or skin of the leaf. These are arranged so as to form 
the openings or mouths about which we have read. By 
means of these mouths the gas makes its way through 
the leaf’s thick skin. 
The plant needs as food the carbon in this gas, 
and so keeps fast hold of it; but the oxygen is not 
needed for this purpose, and so it is pushed back into 
Ehe*aur: * 
Now, we learned in the last chapter of one very great 
service rendered to animals by plants. We learned that 
plants took carbon from the air, and turned this into 
food for animals. 
But there is still another way in which plants serve 
animals. And once more it is the work of Leaf Green 
and Sunbeam that is of such importance to us; for 
when they take hold of the carbon, making it into 
living food for man and beast, they take from the air 
