"What takes place within the structure of the leaf, then, with the aid of the wonderful green workmen, is this: A certain number of molecules of water, brought to the leaf from root and stem, are taken in hand and compounded with a certain number of molecules of carbon extracted from the air that has been brought into the leaf laboratory through its mouths or ta from the outside atmosphere. When the compound has been effected, we still have the atoms of hydrogen and oxygen that composed the water molecules and the atoms of carbon, but they are so marvelously put together that they no longer constitute the liquid water or the gas in which the carbon was imported. They now constitute an altogether new substance which is termed sugar. Thus only three elements are dealt with and these very familiar ones. It would seem as if almost any chemist should be able to manage a simple combination like that. But... no human chemist knows how to manage it. There are forces to be invoked in effecting that combination of which no chemist has any knowledge. Only the chlorophyll grains in the plant leaf have learned the secret, and up to the present they have kept their secret well."