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STEMS

STEMS. And you thought roots were fun. Purpose of Stems. Support leaves Transport water and nutrients Store water and food. WHY?!?. Growth in height only occurs at tip of roots and branches. Specialized Stems. Cactus is a stem that stores food and water for the plant

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STEMS

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  1. STEMS And you thought roots were fun...

  2. Purpose of Stems • Support leaves • Transport water and nutrients • Store water and food

  3. WHY?!? • Growth in height only occurs at tip of roots and branches

  4. Specialized Stems • Cactus • is a stem that stores food and water for the plant • spines are leaves of a cactus

  5. Specialized Stems • Rhizomes • underground stem which grows horizontally through soil • Ex. Iris

  6. Specialized Stems • Bulbs • specialized stems that store food • Ex. onions, tulips, daffodils

  7. Specialized Stems • Corms • Short, swollen underground plant stem used as food storage • Ex. crocuses, gladiolas • Stolons • slender stem that grows above ground • “touch, root-and-shoot” • Ex. strawberries

  8. Where do Stems Grow? • Apical Meristems • cell division occurs at tip of stem • Lateral Meristems • cell division occurs • stems grow in diameter

  9. Structure of stems • Nodes • region on stem where 1 or more new leaves form • Internode • distance between segments • Lenticels • pores in surface of stem • allow gas exchange

  10. Structure of stems • Buds • Terminal - bud at the end of stem • Lateral - buds on side of stem • Bud scales- protective covering over embryonic shoots (present in winter) Lateral Bud

  11. Primary Growth in Stems • Epidermis • outer layer • protection • prevents H20 loss • contains lenticels • allow for O2 and CO2 exchange • Cortex • lies inside epidermis • storage of food for stem

  12. Primary Growth in Stems • Pith • located in center of stem • stores food • Vascular Bundles • Xylem : transfers H2O • Phloem : transfers food

  13. Type of stems • Monocot Stem • **V.B. are scattered** • xylem in center • phloem on outside

  14. Types of Stems • Dicot Stem • **V.B. make a circle** • xylem closer to center • phloem behind xylem

  15. Secondary Growth in Stems • Occurs mainly in dicots b/c monocots lack lateral meristems • Stems increase in diameter due to lateral meristems • 2 types : vascular cambium, cork cambium

  16. Secondary Growth in Stems • Vascular cambium • makes new xylem, phloem through cell division • this becomes secondary xylem & secondary phloem

  17. Secondary Growth in Stems • Wood • is secondary xylem • Heartwood (pith) • is older primary xylem • stopped transporting H20

  18. Secondary Growth in Stems • Sapwood • new secondary xylem • lighter in color (still transports H20) • Bark • protection for woody stems • made up of cork, cork cambium, phloem

  19. Why does bark appear to be rough or crack? • Cells aren’t living • cork cambium produces cork, but dies before maturity • as tree grows, cork ruptures and forms cracks

  20. Annual rings • Springwood • xylem produced in spring • rain is plentiful • cells are larger than summer wood • Summerwood • xylem still produced • limited amt. of water • cells are smaller than springwood

  21. Annual rings • Annual rings • during hibernation xylem isn’t produced • difference from 1 year to the next • can tell app. age of tree • tell environmental conditions • lg.= moist • sm. = drought

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