PRIMARY AND SECONDARY PLANT
GROWTH Page 2
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Page 1
II. Secondary Growth
A. Vascular Cambium
1. Origin
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a. From procambium between
xylem and phloem + parenchyma between vascular bundles in STEMS
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b. From procambium between
xylem and phloem + parts of pericycle in ROOTS
2. Two types of cells
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a. Fusiform Initials (elongated)
-> axial elements = vertical conduction
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b. Ray Initials (isodiametric)
-> ray parenchyma = radial conduction and storage
3. Direction of cell differentiation
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a. Secondary Xylem to inside
of VC accumulates in annual growth rings
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b. Secondary Phloem to outside
of VC and inside older secondary phloem and periderm is crushed and is
eventually lost via periderm
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c. Vascular Cambium is perpetuated
via tangential cell divisions & expansion to maintain VC continuity
through time
4. Secondary Xylem and Phloem
provide physical continuity between Primary Xylem and Phloem of Roots and
Stems
5. Only increases girth of
plant body
6. Human uses of Wood=Secondary
Xylem
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a. Lumber, Veneer,
and Plywood
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b. Paper
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c. Fuel
-
d. Wood distillation
products
-
(Resins, Turpentine, Methanol)
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