1 Review What are three important functions of stems

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• 1 Review What are three important functions of
  stems
• Explain How does the arrangement of vascular
  bundles in monocot stems differ from dicot stems
• Apply Concepts How do the functions of a stem
  relate to the functions of the roots and leaves
  of a plant
• 2 Review Define primary and secondary growth
• Predict Describe what would happen over time
  to a tree sapling that could grow only taller,
  not wider

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Ch 23 Plant Structure and Function

• 23.3 Stems

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Stem Functions

• Stems produce leaves, branches, and flowers
• Stems hold leaves up to the sun
• Stems transport substances throughout the plant.

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Anatomy of a Stem

• Epidermal cells have thick cell walls and a waxy
  protective coating.

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Anatomy of a Stem

• Nodes
• Where leaves are attached
• Buds
• Contain apical meristems that can produce new
  stems and leaves
• Stems produce woody tissue in larger plants.

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Monocot Stems

• Clusters of xylem and phloem tissue are scattered
  throughout the stem
• Ground tissue is fairly uniform consisting mainly
  of parenchyma cells.

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Dicot Stems

• Vascular bundles are arranged in a cylinder, or
  ring
• Pith
• Parenchyma cells inside the ring of vascular
  tissue
• Cortex
• Parenchyma cells outside the ring of vascular
  tissue.

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Primary Growth

• Growth that occurs at the apical meristems.

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Secondary Growth

• Stems increase in thickness to support larger
  plant.

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Secondary Growth

• Very common among dicots and non-flowering seed
  plants such as pines
• Rare in monocots
• Dicots have meristems within stems and roots that
  produce true secondary growth
• Dicots can grow much larger.

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Conifers and Dicots

• Secondary growth takes place in meristems called
• Vascular cambium
• Produces vascular tissues and increases the
  thickness of stems over time
• Cork cambium
• Produces the outer covering of stems.

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• Vascular cambium appears as a thin, cylindrical
  layer of cells between the xylem and phloem of
  each vascular bundle.

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• Divisions in the vascular cambium give rise to
  new layers of xylem and phloem
• Cambium continues to produce new layers of
  vascular tissue each year, causing the stem to
  become thicker.

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Formation of Wood

• Most of wood is actually layers of secondary
  xylem
• Heartwood
• Older xylem near the center of the stem no longer
  conducts water.

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• Sapwood
• Active in fluid transport and is usually lighter
  in color.

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Tree Rings

• Spring growth
• Vascular cambium begins to grow rapidly,
  producing large, light-colored xylem cells,
  resulting in a light-colored layer of early wood
• As growing season continues
• Cells grow less and have thicker cell walls,
  resulting in a layer of darker wood
• Thick rings good growing conditions and thing
  rings poor growing conditions.

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Formation of Bark

• Bark
• All tissues found outside the vascular cambium
• Tissues include phloem, the cork cambium, and
  cork.

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• Cork cambium produces a thick, protective layer
  of waterproof cork that prevents water loss.