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Angiosperms VI Secondary Growth In Stems

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What is secondary growth? Growth in girth of woody plants Tissues derived from cambial layers VASCULAR CAMBIUM produces secondary xylem and secondary phloem CORK CAMBIUM (phellogen) produces cork (phellem) and phelloderm tissues

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Typical Woody Eudicot Stem (overview) Periderm or bark Vascular cambium Secondary xylem Pith

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Woody Eudicot Stem

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Typical Woody Eudicot Stem (detail) Secondary xylem Vascular cambium Rays Secondary phloem (including phloem fibers) Cortex

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Secondary Xylem (angiosperms) Vessels Fibers and tracheids Wood rays Growth rings (annual rings)

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Secondary Xylem (up close and personal) Fibers Tracheids Vessels Ray parenchyma

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Growth Rings Spring (Early) Wood first cells produced by the vascular cambium large cells (good growing conditions) Summer (Late) Wood smaller cells produced toward the end of the growing season poor conditions (cooler, drier) Radical change in cell size allows for recognition of annual growth rings

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Bristlecone Pine (oldest of tree species in North America) 4900 + years old

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Oak Wood in Section Note: thick, multiseriate wood rays

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Other Variations Heartwood darker in color occupies center of the stem, more dense (stronger) deposit of waste products such as resins, gums, oils, and tannins Sapwood lighter in color outer layers, less dense (weaker) contains the sap (dissolved nutrients and water)

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Woody Stem and Periderm sapwood heartwood

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Woody Twigs Terminal bud with bud scales Axillary buds Lenticels Leaf scar

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Twig Structures

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Lenticels Pores in the cork layers which allow for gas exchange in the periderm

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Uses of Secondary Growth Wood Products Various uses based on the density of the wood (often in lbs./cubic foot) Furniture, baseball bats, plywood, pulp products, musical instruments, particle board, artistic pieces, fuel Other Products rope, cinnamon, dyes, drugs (quinine), charcoal, cork, maple syrup

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Cork Harvesting

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Making Maple Syrup 30-50 gallons of sap to make 1 gallon of syrup