They are far more important than mere dress, however. The foods by which the plant lives and grows are made in the leaves. All the food eaten by human beings and other animals can be traced back to plants and the green leaf. Even our bacon and eggs start with plants, for pigs and chickens live on plant food. Without green leaves there would be no animal life on Earth.
Most leaves are broad and very thin, but they have many different shapes.
The needles of the pine trees are leaves. The long ribbon streamers of the seaweeds, the fronds of ferns, the tiny hairs of mosses, the hollow traps in which the pitcher plant catches insects, and the climbing tendrils of the garden pea are also leaves. The leaves of water plants show many interesting differences from those of land plants. In the autumn, leaves turn from green to brilliant shades of scarlet, gold, orange, and purple. Then they finally fall to the ground.