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Diagram to Show Leaf Fall, or Abscission
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Cells at the base of the leaf-stalk divide and form layers of cells across the region where the petiole joins the stem. The inner layers of this new tissue become corky and the vessels become blocked so that the leaf is deprived of water. Before this occurs, the contents of the cell begin to break down chemically, producing the characteristic red and yellow autumnal tints. The cells' contents are digested and the soluble products absorbed back into the tree. The cells beyond the corky layer degenerate, and the dried-up leaf falls, leaving a scar on the stem protected from the entry of bacteria and fungi by impermeable cork. The details of abscission vary in different species.
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