As a very young lad I was told that the summer sun bleached pigment from clothes hung on the line, and saved up the colors to paint on autumn leaves. It occurs to me that solar dryers (a.k.a. laundry lines) and fall leaf colors are similar in that they operate free of charge, but their performance depends on the weather. The same clear-sky conditions that produce dry, good-smelling (and a teensy bit faded) laundry also make for the best leaf color. While the former process is well-understood, the latter is a story fraught with murder and intrigue, and requires some explanation.

Chlorophyll, the green molecule at the center of the photosynthesis miracle, is what makes the world go ‘round. Some say money is, but without chlorophyll the sole life on Earth would be bacteria, whereas without money we’d only have to barter. (Given that both items are green, it’s easy to understand the mistake.) Green gives way to fall colors, though, when trees start killing their own chlorophyll, revealing yellow xanthophylls and orange carotenenoids that were in the leaves all along.

How could a tree be so heartless as to slay its chlorophyll? » Continue Reading.