PRIMARY AND SECONDARY PLANT GROWTH
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PRIMARY AND SECONDARY PLANT GROWTH
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I. Primary Growth <- Apical Meristems
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A. Cell Division
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B. Cell Expansion
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C. Perpetuates itself
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D. Forms cells of primary plant body though cell differentiation
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E. Increases length and girth of plant body
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F. Forms cells that become organized into Secondary Meristems
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G. Components
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1. Protoderm -> Epidermis
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2. Procambium -> Primary Vasculature + Vascular Cambium
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3. Ground Meristem -> Cortex + Pith
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4. Leaf Primordia in SAM (Superficial)
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5. Root Cap in RAM (Internal)<
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II. Secondary Growth
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A. Vascular Cambium
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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 + pericyle in ROOTS
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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
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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
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4. Secondary Xylem and Phloem provide physical continuity between Primary
Xylem and Phloem of Roots and Stems
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5. Only increases girth of plant body
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6. Human uses of Wood=Secondary Xylem
a. Lumber, Veneer, and Plywood
b. Paper
c. Fuel
d. Wood distillation products
(Resins, Turpentine, Methanol)
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B. Cork Cambium
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1. Origin is discontinuous in space and time
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a. New CC made each year to inside of old CC
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b. Initial CC derived from Epidermis or Cortex
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c. Subsequent CC derived from parenchyma in Primary and Secondary Phloem
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2. CC makes Cork Cells toward outside
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3. Because of discontinuity Periderm (Bark) can include:
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a. Epidermis + Cortex
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b. Non Functional Primary Phloem
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c. Non Functional Secondary Phloem
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4. Can be sloughed off, or accumulated into thick ridges & furrows
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5. Special regions of loose cork cells (Lenticels) are produced to facilitate
gaseous exchange from atmosphere to internal living cells.
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6. Human uses of Bark
a. Source of Tannic Acid used in making leather
b. Source of Cinnamon, one of the oldest and most valuable
spices known
c. Phloem Fibers from
1. Flax used to make Linen cloth
2. Hemp used to make Hemp cloth, canvas, cordage
3. Jute used to make Burlap
d. Landscape Mulch
e. Fuel
If you're interested in learning more about Trees,
Wood, and Bark
consider enrolling in Dendrology (BOT 205)
offered every Fall
Semester