Other than in April, when landscapes parade dozens of shades of green before us, it is September when we most notice plant pigments. The fact is these two conditions, spring's greens and autumn's golds, are related to each other.

Looking through a microscope at a plant leaf cell, we can see the tiny, green bodies that make the entire leaf green. If we were to look at a similar cell now, in September, we would see little yellow, orange and red bodies, but no green ones. The green structures, we call them plastids, are gone and have been replaced by more colorful plastids. Actually, the green bodies morphed into yellow, orange or red bodies.

Jerry Davis

In addition to all those changes in pigment-containing plastids, additional colors are manufactured in some leaves. Some red, yellow and purple pigments are floating around in these cells, too. They become may more numerous in autumn, but some cells, like those of beets, always have the purple pigments in their root cells. We see the same purple pigment in the leaves of may woodbine vine leaflets.

All said, plant leaves, young stems, and fruits change color in autumn when green pigments are replaced by more colorful red, orange and yellow pigments. In addition, new pigments are also produced in some plants. But why change color?

A cartoon sketch answered that by saying, "Now the leaves have become what they always wanted to be, more colorful."