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stem structure - external/internal 

  • heartwood - inside, nonfunctional part of stem
    • sealed off w/ lignin
    • only for structure
  • sapwood - functional, still acts as transport
  • external form - primordia (bulges) develops into leaves, shoots, flowers
    • phyllotaxy - leaves arranged 137.5 degrees apart (golden mean)
    • node - region where leaf attaches
    • internode - area of stem between 2 nodes
    • sessile leaf - leaf lacking the petiole (stalk)
    • axillary bud at every axil (between petiole/stem)
    • scars - mark where stems branch off
    • lenticels - pores for gas exchange
  • internal form - apical meristem at stem’s tip produces primary meristems
    • protoderm >> epidermis
    • ground meristem >> parenchyma cells (pith in center, cortex away from center)
    • procambium >> primary xylem/phloem
    • trace - strand of xylem/phloem branching off from the main clinder >> enters developing leaf, flower, shoot >> produces gap
    • periderm - cork cambium, cork, phelloderm found between epidermis and collenchyma
    • outer bark - made of cork tissue


modified stems - most grow erect


  • bulbs - swollen underground stems w/ adventitious roots (ex. onion)
  • corms - similar to bulbs but w/ no fleshy leaves
  • rhizomes - horizontal stems growing underground
  • runners/stolons - similar to rhizomes, but grows on the surface
  • tubers - swollen tips of stolons (ex. potatoes)
  • tendrils - twins around supports (ex. climbing plants like grapes)
Subject X2: 

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