images  and  thoughts

Leaves get their green color from chlorophyll, but they also contain other pigments whose colors are masked during the growing season: carotenoids (yellow) and anthocyanins (orange and red). Why the fall emergence of these other pigments?

In autumn, trees break down their chlorophyll and draw some of the components back into their tissues. Conventional wisdom regards autumn colors as the product of the remaining pigments, which were finally unmasked. In other words, autumn leaves were a tree’s gray hair.

But in recent years, scientists have recognized that autumn colors probably play an important role in the life of many trees. [...] Trees need energy to make carotenoids and anthocyanins, but they can not reclaim that energy because the pigments stay in a leaf when it dies. If the pigments did not help the tree to survive, they would be a waste. What’s more, leaves actually start producing a lot of new anthocyanin when autumn arrives.

The scientists do agree on one thing: the colors are for something. That represents a major shift in thinking.

Carl Zimmer: Those brilliant fall outfits may be saving trees, The New York Times, Oct. 19, 2004.

Virginia creeper above our garage door in Boulder, CO.

If the gray hair does not help us to survive, it’s a waste.