14) Secondary Growth of Plants

14) Secondary Growth of Plants - cannot keep pace since...

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AP Biology Secondary Growth of Plants 1) Main purpose = to enlarge (widen) in diameters; adds girth to stems and stems in woody plants 2) Works by the interaction of two cambiums: vascular cambium and cork cambium Vascular Cambium = Adds secondary xylem (wood) toward the inside = Adds secondary phloem (barks) toward the outside Cork Cambium = Adds tough layers for prevention of water loss or any invasion of pathogens; this occurs by replacing the epidermis of the outside 3) Also, we need to differentiate two terms: periderms and bark Periderm = the addition of cork cells and cork cambium Bark = all tissues external to the vascular cambium (secondary phloem, bark cambium, and cork) 4) Secondary Growth of a Stem First Lateral Meristem (Vascular Cambium) a) After completion of primary growth, the vascular cambium (1 st lateral meristem) is formed b) This vascular cambium forms secondary xylem to the inside & secondary phloem to the outside c) As the vascular cambium adds more cells, other tissues outside of the cambium
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Unformatted text preview: cannot keep pace since there are no more cells to divide d) These non-growing tissues are destroyed Second Lateral Meristem (Cork Cambium) e) The cork cambium is formed from parenchyma cells in the cortex f) The cork cambium produces cork cells; they replace the epidermis and non-growing parts g) More cork cells are produced as the stems diameter increases 5) Mechanism of Secondary Growth Produced by the Vascular Cambium a) A cambial initial can divide to form 2 cambial initials; multiple divisions of cambial initial results in the complete formation of vascular cambium: Periclinal Division b) A cambial initial can be differentiated into either a secondary xylem cell (X) or secondary phloem cell (P) with significant elements for each cell (vessel elements, companion ells, tracheid, and etc.): Anticlinal Division Figure 1 <Figure 1> Anticlinal Division & Periclinal Division...
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14) Secondary Growth of Plants - cannot keep pace since...

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