The mixture of red, purple, orange and yellow is the result of chemical processes that take place in the tree as the seasons change from summer to winter.
Leaves are nature’s food factories. Plants take water from the ground through the roots and the gas called carbon dioxide from the air.
During the spring and summer the leaves serve as factories where most of the foods necessary for the tree’s growth are manufactured. Plants turn water and carbon dioxide into oxygen and sugar through a process called photosynthesis, which means putting together with light. This food-making process takes place in the leaf in numerous cells containing chlorophyll, which gives the leaf its green color.
Along with the green pigment are yellow to orange pigments, carotenes and xanthophyll pigments which, for example, give the orange color to a carrot. Most of the year these colors are masked by great amounts of green coloring.
But in the fall, the days get shorter. Because of changes in the length of daylight and changes in temperature, the leaves stop their food-making process. The chlorophyll breaks down, the green color disappears, and the yellow to orange colors become visible and give the leaves part of their fall splendor.
At the same time, other chemical changes may occur, which form additional colors. Some mixtures give rise to the reddish and purplish fall colors of trees such as dogwoods and sumacs, while others give the sugar maple its brilliant orange.
The autumn foliage of some trees shows only yellow colors. Others, like many oaks, display mostly browns. All these colors are due to the mixing of varying amounts of the chlorophyll residue and other pigments in the leaf during the fall season.
As the fall colors appear, other changes are taking place. It is at this point where a special layer of cells develops and gradually severs the tissues that support the leaf. At the same time, the tree seals the cut, so that when the leaf is finally blown off by the wind or falls from its own weight.
Most of the broad-leaved trees in the North shed their leaves in the fall. However, in the South, where the winters are mild, some of the broad-leaved trees are evergreen; that is, the leaves stay on the trees during winter and keep their green color.
Only some trees loose leaves. Most of the conifers — pines, spruces, firs, hemlocks, cedars, etc. — are evergreen in both the North and South. The needle- or scale-like leaves remain green or greenish the year round, and individual leaves may stay on for two to four years or more.
It is the combination of all these things that makes the beautiful colors in the fall. Enjoy the colors; they only occur for a brief period every year, during autumn/fall.
From the Internet