© Janet Davis

October means apples. And apples mean that the Joni Mitchell circle game that started with those first plump buds in April finally comes all the way around in autumn-- with the help of buzzing bees, bountiful sunshine and brimming bushel baskets.

Apples ripening for picking just as red and gold leaves flutter down from maples and birches are flip sides of the same botanical coin. Both demonstrate the common mechanisms that nature employs to bring the growing season to an end: a process described by the lovely word "senescence". Defined as the breakdown of a plant’s cellular structures leading to death, it shares the same root as the word "senility", but without the negative connotation. For although built-in obsolescence is something we decry in cars and computers (and humans, for that matter), it’s a fact of life in apples and maples. And it all has to do with ethylene.

Ethylene. Four hydrogen atoms, two carbon atoms, and one of the simplest plant hormones known, but absolutely essential if the maple is to survive winter and the apple tree’s fruit is to sweeten and turn red. Ethylene is a gas that causes cell walls to soften and membranes to deteriorate. So if you’re standing under a brilliant sugar maple as the leaf stems twist, break and fall, you’re seeing ethylene dissolve the starchy cells between the petiole and the twig. And if that dropped banana soon forms a dark bruise, you’re witnessing the production of ethylene by the damaged cells. And if you’re tucking green tomatoes into paper bags in the basement to ripen, you’re hoping for the effects of trapped ethylene. And if you’re removing one rotten orange from the crisper to keep its neighbours from spoiling, you’re preventing ethylene from doing its job.

So if ethylene is the agent of ripening and death, what triggers the plant to grow, flower and bear fruit? That would be auxin, the hormone of growth, flowering and fruiting. But that’s a story for an entirely different season.

Adapted from an article that appeared originally at Chapters Online.

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