Fiery foliage

摘要

Just as everything in the garden, including the gardener, appears to be winding down with a deep sigh, foliage explodes into autumn colour. GRAHAM RICE picks through the fallen leaves to find the best plants for a memorable display. Why do the leaves of so many trees turn flaming and fiery in autumn? Usually the only part of a plant that's colourful is the flowers, which need to attract pollinating insects. So why do trees spend so much effort in what seems, from a biological point of view, such apointless exercise? In fact, they're not wasting effort; the trees are actually doing the exact opposite, conserving resources. As the days shorten, temperatures cool and light levels drop, chemical changes take place in the foliage which allow carbohydrates and other reserves to be moved back down into the woody structure of the plant, to be stored until the following spring. The dramatic foliage colouring is simply a by-product of these chemical reactions, evidence of the useless chemicals left behind