Introduction to Wood Anatomy

I.  Plants increase in size through concerted processes of
     A. Cell division = mitosis + cytokinesis
     B. Cell expansion = turgor pressure leads to elastic
          expansion of cell wall

II. Plant Cell Walls
     A.Composed primarily of cellulose, with various amounts of
          other molecules
     B. How plants stand up to gravity
          1. Primary cell walls + turgor pressure  
          2. Secondary cell walls of dead cells

III. Growth of a plant stem

     A. Primary Growth via Shoot Apical Meristem
          1. Increase in length and girth
          2. Epidermis
          3. Cortex
          4. Procambium -> 
               a. Primary Phloem
               b. Fascicular Cambium -> Vascular Cambium
               c. Primary Xylem
          5. Pith

     B. Secondary Growth via Vascular Cambium 
          1. Increase in girth only
          2. Structural support
          3. Maintains continuity in Transport Pathways
               a. transpiration in xylem
               b. translocation in phloem
          2. Toward the end of primary growth
               a. Formation of Fascicular Cambium from Procambium
                  + formation of Interfascicular Cambium from
                    Primary Ray Parenchyma
               b. Vascular Cambium forms via merger of Fascicular
                    and Interfasicular Cambia
               c. Cell Division + Cell Expansion of cells
                    comprising Vascular Cambium give rise to
                    1. Secondary Xylem to inside
                    2. Vascular Cambium laterally
                    3. Secondary Phloem to outside
          3. Massive stem trunks of trees and shrubs are produced
               by cyclic periods of cell division + cell expansion
               in vascular cambium (& cork cambium)
               a. Period of dormancy
               b. New secondary xylem formed first to outside of
                    existing xylem
               c. New secondary phloem then formed to inside of 
                    existing phloem
               d. As development and accretion of new seconday
                    xylem increases girth of stem, new vascular
                    cambium cells develop to maintain continuity
                    of the vascular cambium cylinder

     C. Secondary Growth via Cork Cambium
          1. Increase in girth only
          2. Provides protection against 
               a. water loss
               b. desease vectors
               c. fire
          3. Lenticels provide regions of gaseous exchange
          4. Initial cork cambium may be derived from
               a. Epidermis
               b. Cortex
          5. Subsequent cork cambia derived 
               a. Interior to initial cork cambium
               b. Cortex
               c. Parenchyma within primary or secondary phloem
          6. Cork cambia can be continuous or discontinuous
          7. Most of the cells derived from cork cambium are
               a. to the outside
               b. heavily suberized and dead at maturity
          8. Bark texture is anatomically complex
               a. Continuity of cork cambium
               b. Types of cells that are incorporated from
                    secondary phloem into outer bark