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LEAF SCAR, VASCULAR BUNDLE SCARS, and LENTICELS IN AILANTHUS (Ailanthus altissima) TREE-OF-HEAVEN. In the fall the base of the petiole (leaf stalk) forms a weak zone called an Abscission Layer. When the leaf falls a healing layer (cork) develops on the stem which closes the wound, thus forming the leaf scar. Leaf scars are found on many winter twigs and sometimes aid in their identification. The Vascular Bundle Scars seen inside the leaf scar, represent vascular tissue that connected the leaf and stem and broke off. A lateral bud is also seen in the image closely associated with the leaf scar. The Lenticels are the very numerous small light structures, and function in gas exchange of oxygen and carbon dioxide. Ailanthus is a very hardy, introduced tree, native from China. Michigan