Botany 1404: Stems

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Botany 1404: Stems
2012-01-27 20:33:32
botany stems

Basics of stems
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  1. The Shoot
    • composed of stem and leaves
    • has axillary and terminal buds
  2. Functions of the Stem
    • support
    • conduction of water, minerals, and food
  3. Organisation
    • buds: terminal and axillary
    • bud scales
    • Nodes: comprised of axillary bud and leaf. Can have multiple leaves attached.
    • Internodes are the space between nodes.
  4. Shoot Tip
    • has the shoot apical meristem
    • phytomere; has axillary bud, node, internode, and leaf.
    • Leaf primordia; develops into leaves
    • Axillary primordia; develops into lateral shoots
    • trichomes (small extentions of epithelial cells)
  5. Dicots
    • epidermis: single layer of cells, cuticle over it.
    • Cortex composed of collenchyma and parenchyma cells
    • Vascular bundle (xylem, phloem, vascular cambium)
    • Pith composed of parenchyma cells
  6. Monocots
    • epidermis: single layer of cells, cuticle over it
    • no pith/cortex regions, just ground tissue
    • vascular bundle (xylem, phloem, bundle sheath, airspace)
  7. Growth
    • annuals: go through their entire life cycle in one year, limited secondary growth, generally herbaceous
    • Biennials: two seasons needed to complete entire life cycle, limited secondary growth, generally herbaceous
    • Perennials: vegetative structures live year after year, undergo secondary growth, can be herbaceous or woody.
  8. Vascular Cambium
    • monocots have no vascular cambium
    • vascular cambium produces secondary xylem and phloem.
    • When 2 cells go out, 1 differentiates.
    • it alternates differntiation between xylem - phloem
    • rings on trees are rings of xylem
  9. Cork Cambium
    • outside part of stem
    • produces cork cells to outside and cork parenchyma (phelloderm) to the inside
    • produces periderm
  10. Secondary Growth in Stems
    • within vascular bundle, the fasicular cambium forms from the procambium.
    • In pith rays, interfasicular cambium forms between bundles.
    • at the end, remnants of cortex, pith, and epidermis.
    • peridem forms
  11. Periderm
    • 3 parts
    • cork cambium: lateral meristem that produces cork and phelloderm.
    • cork: heavily suberized walls, non-living.
    • cork parenchyma: phelloderm, living.
  12. Lenticels
    region of cork that allows gas exchange between intracellular spaces and the atmosphere.
  13. Bark
    • all tissues outside of vascular cambium (cork cambium, cork parenchyma, cortex, secondary phloem).
    • inner bark (living bark, tissue between vascular and cork cambium)
    • outer
  14. Secondary Phloem
    • phloem that is nonconducting is nonfunctional phloem
    • functional phloem is conducting.
  15. Wood
    • secondary xylem is wood
    • has a combination of tracheids, vessel fibers, fibers, and parenchyma cells.
  16. Growth Rings
    • Occur in temperate regions (regions with seasons)
    • periodic activity in vascular cambium produces growth in secondary xylem and phloem (growth rings)
    • more water available = bigger xylem cells = thicker ring
    • Factors in rings: temp, light, species, soil water availability, rainfall, and length of growing season.
  17. Heartwood
    • darker, non-conducting wood
    • provides structural support
    • dead tissue
  18. Sapwood
    • lighter
    • conducts water and ions
    • dead tissue
  19. Cladophylls
    • stems resembling leaves
    • ex: prickly pear
  20. Thorns
  21. Rhizomes
    underground stems
  22. stolons
    stems growing along surface of ground
  23. Tubers
    • storage
    • ex: potatoes
  24. Corms
    • w/contractile roots
    • ex: bulbs
  25. Bulbs
    • storage
    • ex: onion