Sunday, November 4, 2012

Exothermic Plants?

Last night came the first genuine frost of the year. In preparation late yesterday Brigitte was out in the yard “covering” the few plants that still remained outside. These would, in fact, winter out there, but she still wished to harvest some of them. I saw the results this morning and got curious about the mechanism of frost protection. Unlike the orders above the vegetable kingdom, which are heat-producing (exothermic), plants are heat-consuming (endothermic). So why does covering plants protect them?

The simple answer from the plant-raising community (link) is that a covering them keeps cold air from reaching the moisture on plants’ leaves and buds. The ideal cover is some kind of natural fabric able to breathe: cotton, linen, newspapers, burlap. Moisture escapes. Covering plants with plastic is a distinctly inferior tactic. Moisture will accumulate, and if the overall temperature drops low enough, the frost damage will be much greater, cover or no cover.

In this process of trying to discover the mechanism of protection, I came across something interesting. Some plants are exothermic. They generate heat—and often quite a lot of it (link). Two examples—and everybody on this subject names them—are the Voodoo Lily (shown on left above) and Skunk Cabbage (shown on the right); the illustrations come from Wikipedia. Curiously these plants do not make heat to keep warm, although that is a by-product. The Voodoo Lily, which has a rotting smell, uses heat to spread the odor in order to attract flesh-eating insects which then, disappointed after they arrive (no meat anywhere) nonetheless serve to pollinate. The Skunk Cabbage is suspected of the same tactic. Tricky, tricky.  Reminds me of car companies that sell cars by showing sexy, mysteriously smiling females. Buy the car and—well, there is no girl inside.

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