Pigment

(From Kids InfoBits, a Gale online resource)

When the autumn season arrives, nature seems to color the landscape. Leaves on trees that have been green since spring all of a sudden turn to bright red, orange, yellow, rust and brown. How does this happen? Pigment is what creates colors. Green leaves contain the pigment chlorophyll, which helps make food for the tree. Like some animals that hibernate, plants slow down and rest in winter. During this period, trees stop growing so they don't need as much food. The shorter days and cooler temperatures of autumn signal the tree to begin its "dormant" period. In deciduous trees (those that drop their leaves), the dormancy process first shows in the leaves. When the tree shuts down its food-making process, a layer of cells forms at the end of each leaf where it's attached to the twig. Just like a cork in a bottle, this layer of cells stops the flow of moisture to the leaf. When this happens, chlorophyll is no longer needed to help produce food for the tree. Leaves contain yellow and orange pigments all the time, but the green chlorophyll hides them during the growing season. When the leaf is sealed off from the twig, the chlorophyll begins to disappear. Then, almost like magic, the yellow and orange leaves begin to appear.