Secondary Growth in Stems

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Secondary Growth in Stems

• Ch. 26

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Objectives Define Comprehend

• How a plants girth increases
• The effects of 2cd growth on primary stem
• Bark
• Wood
• Conifer vs. angiosperm wood
• Growth rings
• Sapwood vs. heartwood

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How does a plant body increase in girth??

• Secondary growth derives from lateral meristems
• Vascular cambium
• Cork cambium

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Effects of secondary growth on primary stem
Pith rays produce interfascicular cambium
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Interfascicular fascicular cambium produce
Vascular cambium
Cortex produces cork cambium, which produces
periderm
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Periderm
Cortex
Primary Phloem fibers
Secondary Phloem
Vascular Cambium
Secondary Xylem
Primary Xylem
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Wood Secondary Xylem

• Conifers (softwood) lack vessels
• Have long tapering tracheids
• Pines have resin ducts
• Thought to protect the plant from decay-producing
  fungi and bark beetles

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Growth rings result from periodic activity of the
vascular cambium

• In temperate regions, the v.c. is dormant during
  the winter reactivates in the spring
• Width may vary due to rainfall, temp, light, etc.

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Sapwood vs. Heartwood?
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Good diagram to study
Periderm
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Questions that you should be able to answer

• Pg. 580 3, 4, 5a, and 6