We are well into November and a lot of trees still have their leaves on. However, the leaves did not have their usual fall color and are brown. What is going on?
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Colorado Public Radio - Royalty Free Stock Photos
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The process of leaves falling involves an understanding of the abscission zone, which is the area between the leaf petiole (leaf stalk) and the branch. The accompanying picture shows the leaf, petiole, branch, and abscission zone. In the abscission zone there are two sets of cell structures, one set of cells is attached to the petiole and the other set of cells are attached to the branch. In a normal fall, the cells attached to the petiole become weaker since the photosynthesis process in the fall is lower. This is the time that the leaves start to turn color as the green covering on the leaves disappears, leaving the natural reds, oranges, purples, and yellows to give the trees their fall beauty. As the days go on, the cells closer to the petiole weaken and can’t hold the leaves on. Thus, the leaves fall off. Meanwhile, the cell structure that is attached to the branch covers up the wound that is left after the leaf falls off. This is to prevent moisture loss from the wound to aid the tree in surviving through the winter.
