j62 THE FAIRY-LAND OF SCIENCE. 
up the oxygen in it and send back out of our mouths 
carbonic acid, which is a gas made of oxygen and 
carbon. 
Now, every living thing wants carbon to feed upon, 
but plants cannot take it in my itself, because carbon 
is solid (the blacklead in your pencils is pure carbon), 
and a plant cannot eat, it can only drink-in fluids and 
gases. Here the little green cells help it out of its 
difficulty. They take in 
or absorb out of the air 
the carbonic-acid gas 
which we have given out 
of our mouths, and then 
81- by the help of the sun- 
waves they tear the car- 
bon and oxygen apart. 
Flo. 42.-Oxygen-bubbles rising Mogt ^ 
from laurel-leaves in water. J & * 
throw back into the air 
for us to use, but the carbon they keep. 
If you will take some fresh laurel-leaves and put 
them into a tumbler of water turned upside-down in 
a saucer of water, and set the tumbler in the sunshine, 
you will soon see little bright bubbles rising up and 
clinging to the glass. These are bubbles of oxygen 
gas, and they tell you that they have been set free by 
the green cells which have torn from them the carbon 
of the carbonic acid in the water. 
But what becomes of the carbon? And what use 
is made of the water which we have kept waiting all 
this time in the leaves? Water, you already know, 
is made of hydrogen and oxygen; but perhaps you 
will be surprised when I tell you that starch, sugar, 
