DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY
Leaf scar (light brown) on the branch of a horse chestnut tree (Aesculus hippocastanum). This scar, also known as an abscission zone, was produced when a leaf attached to the branch was shed by the tree in early autumn. Before the leaf detached, the tree formed a horseshoe- shaped area of cork-like material on the branch. This protects the tree from dehydration and infection once the leaf has been lost. The characteristic shape of the abscission zone gives the tree its common name.
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