Chapter 33: Stems
varied

  1. support the leaves
  2. internal transport
  3. make new living tissue(buds-meristematic):branch, new leaves, flowers
  4. reproduction-asexual fashion
  5. photosynthesis(if green)
  6. storage(CHO)

Woody Stems-have secondary growth
Vascular cambium produces: 1)secondary phloem to its exterior 2)secondary xylem to its interior
Year one: herbaceous stem(dicot)
Year two: begin secondary growth
  1. vascular cambium becomes continuous
  2. divide(vascular cambium)
  3. new secondary phloem pushes out the old primary phloem; new secondary xylem pushes and crushes the pith and primary xylem
  4. cortex, epidermis sloughed off
cork parenchyma and cork cambium:
came from de-differentiated parenchyma>>>cork cambium>>>periderm
cork cells dead at maturity, have suberin (water-proofing, reduces water loss and soaking in)

Types of Wood-
  1. sapwood-young wood, close to bark, functional
  2. heartwood-older wood, close to center, non-functional, denser, better support
  3. hardwood-wood of angiosperms
  4. softwood-wood of gymnosperms
  5. annual rings-rings of growth in spring and summer (spring-few fibers, thick layer; summer- more fibers, thin layer) (1632 B.C. Mt. Thera erupted on Crete, layer of ash in rings of old trees)
  6. knot- dead branch surrounded by growing wood
  7. transport of stems-one way (water up, sugar down)

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