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primarystem213-page4 - Cucurbita stem vascular tissue is an...

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The Shoot System: Primary Stem Structure - 4 Vascular Tissue Pattern 1: Ring of discrete vascular bundles with pith rays Vascular bundles may have a fiber bundle cap (which is called a phloem fiber cap because it is adjacent to the phloem) or a simple sheath of sclerenchyma surrounding the entire vascular bundle. Individual bundles are separated from each other by pith rays, parenchyma tissue that extends from the interior pith region of the stem to the cortex. Primary Phloem is found toward the exterior of the vascular bundle. (Some vascular bundles also have phloem on the inside of the xylem, too.
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Unformatted text preview: Cucurbita stem vascular tissue is an example of this.) • Primary Xylem is found toward the interior of the vascular bundle. • When there is secondary growth, there will be a layer of procambium retained between the primary xylem and primary phloem. Such vascular bundles are said to be open vascular bundles, because they can proceed to secondary growth. • Eudicots that lack secondary growth have closed vascular bundles, and no procambium remains between the primary xylem and primary phloem. Eudicot open vascular bundle Closed vascular bundle...
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