DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Leaf abscission layer. Light micrograph of a longitudinal section through a dicotyledon stem that has undergone leaf-fall. Part of the abscission layer (orange) is at centre. This layer is at the base of a leaf stalk where it meets the stem. The orange tissue is cork (laid down by a meristematic layer of cells, the phellogen), and made up of dead cells. When the leaf falls off, this scar of cork prevents the ingress of pathogens, loss of water, and insulates the stem against fire damage. Magnification: x230 when printed at 10 centimetres high.
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