secondarygrowth213-page15

secondarygrowth213-page15 - internode. Nodes and internodes...

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Secondary Growth in Stems: Wood, Bark and Surface Features - 15 External Features of Stems Before we leave our discussion of secondary growth and stems, we should spend a bit of time discussing the external features of twigs – young wood stems and branches. There are a number of easily recognized common surface features of the twigs of any woody stem, particularly when dormant. In fact, there are identification keys that focus on winter twig and bud patterns, particularly for deciduous trees. Most twigs have a terminal (or apical) bud, located at the tip of the twig, as well as a number of axillary (or lateral) buds, located in the axils of leaves. Dormant buds are protected by one to several bud scales, which are modified leaves. Leaves are attached to the stem at nodes; the space along the stem between leaves is called an
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Unformatted text preview: internode. Nodes and internodes are distinctive on twigs with or without their leaves attached. A leaf scar remains on the stem when leaves dehisce. The pattern of leaf scars is a species characteristic. The vascular bundles of the leaf petiole also leave bundle scars within the leaf scar. Each growing season, a ring of bud scale scars that protected the dormant terminal bud can be seen on twigs. This is one way to determine the age of a twig or branch. Lenticels are also more visible on twigs than on older stems where the bark patterns may mask them. As secondary growth continues, and branches increase in girth, the expansion of cork and bark eventually replaces the features found on twigs. Older branches take on the bark pattern associated with the specific species....
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