Only certain cells can do this special piece of work. Only the cells which hold the green substance that colors the leaf can tear apart carbonic-acid gas. Every little cell which holds a bit of this leaf green devotes itself to separating the carbon from the oxygen.
Why this special power lies in a tiny speck of leaf green we do not know. We only know that a cell without such an occupant is quite unable to break up carbonic-acid gas.
But even the bit of leaf green in a tiny cell needs some help in its task. What aid does it call in, do you suppose, when it works to wrench apart the gas?
In this work the partner of the bit of leaf green is nothing more or less than a sunbeam. Without the aid of a sunbeam, the imprisoned leaf green is as helpless to steal the carbon as you or I would be.
It sounds a good deal like a fairy story, does it not,—this story of Leaf Green and Sunbeam?
Charcoal is made of carbon. About one half of every plant is carbon.
The coal we burn in our fireplaces is the carbon left upon the earth by plants that lived and died thousands of years ago. It is the carbon that Leaf Green and Sunbeam together stole from the air, and turned over into the plant.
If one looks at a piece of coal with the eyes which one keeps for the little picture gallery all children carry in their heads, one sees more than just a shining, black lump. One sees a plant that grew upon the earth thousands of years ago, with its bright green leaves dancing in the sunlight; for without those green leaves and that sunlight, there could be no coal for burning to-day. And when we light our coal fire, what we really do is to set free the sunbeams that worked their way so long ago into the plant cells.
It is more like a fairy story than ever. Sunbeam is the noble knight who fought his way into the cell where Leaf Green lay imprisoned, doomed to perform a task which was beyond her power. But with the aid of the noble Sunbeam, she did this piece of work, and then both fell asleep, and slept for a thousand years. Awakening at last, together they made their joyful escape in the flame that leaps from out the black coal.
In truth, a sunbeam and a flame are not so unlike as to make this story as improbable as many others that we read.