lecture 11

• Vascular cambium


  Lateral meristematic tissue that runs between xylem and phloem. It adds more of those tissues, widening the shoot.

  
• Cork cambium


  Lateral meristematic tissue that produces a tough, thick, waxy covering called cork.
• Secondary growth


  1. Vascular cambium grows in circumference and adds cells to itself

  2. Inner xylem tissue grows unevenly across seasons, leading to annual rings

  3. Secondary phloem does not keep pace with stem thickening, older layers become bark

  
• Cork


  • Tissue of compacted cells that also makes suberin, waterproofs the stem, prevents leakage, and impairs attacks
  • Lenticels, regions of loose cork that allow diffusion of gases into stems, form in the cork layer
• Layers of a tree trunk or branch


  • Sapwood
  • Heartwood

  
• Cut out volume from tree


  • Only fully removes heartwood, VC and sapwood layers still intact enough
  • Phloem layers still being made by VC
  • New lateral meristem tissue forms around the cut out section
  • Old trees like coast redwoods die very slowly
• Nail sign into tree


  Sign height will be much higher off the ground in 20 years
• Cohesion


  Water molecules like to stick to each other by hydrogen bonds
• Evaporation


  Water -> water vapor, requires energy to break H-bonds
• Transpiration


  Loss of water vapor from leaves
• Mechanisms of water movement


  • Osmosis
  • Active transport
  • Bulk flow
• Water potential


  The physical property that predicts which direction water will move, typically measured in megapascals (MPa)
• Solute potential


  Negative when solutes are present, pure water is defined as 0
• Pressure potential


  Also called turgor or tension pressure, a positive pressure potential
• Key terms


  • Annual rings
  • Cork
  • Bark
  • Heartwood/sapwood
  • Hydrogen bonds
  • Cohesion
  • Tension
  • Evaporation
  • Transpiration
  • Active transport
  • Osmosis
  • Bulk flow
  • Water potential
  • Solute potential
  • Pressure potential