MadSci Network: Botany |
Leaves are juicy and green because those are the things that let the leaf make food for the rest of the plant. The juicy part is mostly water and the green is a colored substance called chlorophyll. These two things along with a gas from the air (called carbon dioxide) are used by the plant to make food for itself. But the plant cannot make food for itself when it is cold. So when the weather starts to get cold, the plant stops making chlorophyll and stops the flow of water from the roots into the leaves.
There are other colored substances (called pigments) in the leaves besides chlorophyll and when the chlorophyll disappears these other pigments become visible in the spectacular fall foliage displays that are beautiful to see. All of these colors last only a short time, however, before the layer which blocks water from the leaves hardens and the leaf's connection to the rest of the tree is cut off.
If you can, adopt a tree and watch closely what happens to it and some individual leaves on the tree over a whole year.
Try the links in the MadSci Library for more information on Botany.