The colors of fall

The leaves are falling off the trees pretty quickly here in New England, but only after putting on a fantastic color display this year. I haven't seen blazing foliage like that in a while.

But where do those colors come from? What causes that fiery display? As we all learned in high school biology class, the green we see in the leaves from spring through summer is caused by chlorophyll - the pigment that captures sunlight for photosynthesis. As the temperatures drop and the days get shorter, leaves stop producing chlorophyll. And here's the trick. The orange and yellow pigments, called carotenoids, are already there...the leaf produces them at the same time that it produces the chlorophyll, but they are masked by the intensity of the green coloring. Once the green is gone, the orange and yellow can show through.

As for the reds, they come from pigments called anthocyanins - and these are a little more mysterious. They are only produced in the fall, act as a kind of antifreeze and sunscreen for the leaves, and, interestingly enough, can be a sign of a tree in distress (a tree that turns red early is in some trouble).

In nature, you often find that brilliant colors are a signal for danger or distress. Me, I like to think of these colors as a sign that my favorite season is here.

[Read more at MSNBC.]