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Lecture 12 - Lecture 12 Secondary Roots Secondary Roots Fig...

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Lecture 12 - Secondary Roots Secondary Roots – Fig. 24-15 Reminder: - increase in girth is the result of secondary growth (See pages: pp. 569-571, 615-617 8 th ed; 538-540, 580-583, 7 th ed) - lateral meristems give rise to secondary growth Keep in mind: Anticlinal vs Periclinal Anticlinal divisions: perpendicular to plant surface Periclinal divisions: parallel to plant surface Two lateral meristems (cambia à bidirectional divisions) – Fig. 24-23: Why are secondary roots important? - Provides anchorage and support as the upper part of the plant gets larger Secondary Growth in Roots is due to Two Lateral Meristems : (Fig. 24-15c-d,e,f; Fig. 24-16) A. Vascular Cambium à SECONDARY XYLEM AND SECONDARY PHLOEM - Vascular cambium develops by mitosis (periclinal divisions) of residual (undifferentiated) procambial cells that persist between primary phloem and primary xylem (Fig. 24-15c) - Pericycle opposite protoxylem poles begins to divide and forms the closed circle of vascular cambium around the xylem.
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