One of the Secrets of the Universe

What makes the colors of the leaves change? As the colors on the trees turn from green in August, to yellow and red and orange in September and October, and finally to brown in November, I often wonder about the miraculous and beautiful changes in the colors.

Certainly, the leaves turn color as the temperature gets colder. And this is related to the days getting shorter and the nights longer. So both the temperature and the amount of daylight influence the colors of the leaves. Also the amount of precipitation toward the end of summer plays a role in how long it takes the leaves to turn and how long they stay on the trees.

But I noticed something intriguing on my walk today in the neighborhood. It is a clue about the changing colors of the leaves.

There is a bush that I walk past on every walk I take, and today many of the leaves on this bush were brilliant yellow, so I stopped to look a them. Tiny, oval, bright yellow leaves. Some of the leaves on this bush were still green, and a small number had turned from yellow to reddish brown, but what caught my attention were the brilliant yellow leaves.

I began collecting specimens of the leaves of different colors, when my attention was drawn to a reddish brown leaf. Then I noticed another reddish brown leaf right behind the first one and in contact with it, with only about half of this second leaf showing. When I looked more closely and separated the 2 leaves, I was startled and delighted! While the foreground leaf was entirely reddish brown, the background leaf had remarkable coloring. It was reddish brown where the light could fall, and bright yellow where it was in the shadow of the other leaf. There was a sharp line where the color changed from brown to yellow, not a gradual change, but as clearly marked as if by a shadow.

This was a dramatic demonstration that the daylight itself was causing the leaf colors to change! And where the light was blocked, the changes were less. It was awesome -- I felt as if I had just been shown one of the secrets of the Universe.

For most trees and bushes, the spacing of the leaves allows light to fall everywhere. So the light is not often blocked by one leaf from another.

And then I remembered something else I had noticed this year more than any other. As the leaves turned color, tree by tree, the leaves on the outside were reddest, then orange inside, and then yellow closest to the trunk. And this happened for the same reason, I think, as the tiny reddish brown leaf which had a yellow part where it was in the shadow of another leaf. The leaves on the outside of the tree get more light, and they shade the leaves to the interior.

So I thought I was just going on a walk today when I left the house in the brisk morning air. Little did I know that I would be shown one of the secrets of the Universe!