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Earlier this week gales and rain finally swept leaves from the trees, and the glorious show of autumn colour came to a sudden end. Yet if this was a disappointment for humans, for the trees it was merely the completion of their summer labours.

Leaves turn gold and red when the green chlorophyll in them is reabsorbed into twigs and branches, and other chemical compounds show through. As far as biologists can tell, the different colours serve no biological purpose - but once the tree has taken back as much nutriment as it can from the leaves, it dumps the residue.

Shedding leaves is also a means of saving water. In winter, when the earth is cold, a tree cannot absorb much water through its roots, and if moisture continued to evaporate through the leaves, the whole organism would dry out. The fall, in short, shows that the tree has shut down for a good long rest until the spring.

Duff Hart-Davis