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Half of the Procambium usually produces Phloem. Phloem is generally opposite the Xylem and nearer to the Epidermis. The inner Procambial cells produce Xylem. | ||
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The first step in xylem differentiation is cell enlargement. This establishes the pattern in which Tracheary Elements will differentiate. The innermost xylem cells have the narrowest diameter. Those at the opposite pole have the largest diameter. | ||
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The next step is the deposition of
thick, lignified secondary cell wall in the walls of Tracheary Elements. The first cells
to develop these secondary walls are those with the smallest diameters near the center of
the stem. These cells are called Protoxylem. Proto = First |
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This continues centrifugally (away from the center). This is called Endarch |
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Eventually, all of the Procambium cells destined to become Xylem differentiate! |
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Syllabus |  |
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