Davy sat thinking silently about this, but little Prue did not quite understand.
"I suppose you mean that the plants made us healthy to work in them," she said.
"I mean that, and I mean a great many other things. In the first place, plants furnish all the food in the world. Not only the vegetables, but the animal-food. Our turkey would not have been here to-day if he had not been fed on grain, and even the oysters must live from a sort of plant-food in the sea. Every creature that walks or flies or swims lives either on plants themselves or from some creature that does live on them."
"Do sharks live on plants, too?" asked Prue.
"Of course!" said Davy. "Sharks eat men, and men eat plants."
"I don't suppose sharks live altogether on men," laughed big Prue, "and the little fish they eat may live on other little fish, but if you go far enough you will find that somewhere the beginning is plant-life."
"Plants also warm and light us," went on the Chief Gardener. "Every stick of wood, or bit of coal, or drop of oil we burn, comes from plant-life. The coal was vegetation long ago—very long ago—and the heat and light that come from it were stored there in that far-away time by the green leaves that drew in life and light from the sunbeams."
"Do the leaves really take up light?" asked Davy.
"They really do. With every particle of vegetable matter that is made, a portion of the sun's heat and light is laid up in it. The light is still in the coal, though it looks so black. We have only to burn it, to get back the sunlight."