The various kinds of stems differ in structure. Herbaceous stems have only <I>primary tissues,</I> which develop from cell division at the tip of the stem. Woody stems have both primary and <I>secondary tissues.</I> Secondary tissues cause woody stems to develop wood and bark and to grow thicker. These diagrams show the internal structures of the herbaceous stems and of a woody stem.
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World Book diagrams by Marion Pahl</P>
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