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)