PRIMARY AND SECONDARY PLANT GROWTH

     I. Primary Growth <- Apical Meristems

          A. Cell Division

          B. Cell Expansion

          C. Perpetuates itself

          D. Forms cells of primary plant body though
             cell differentiation

          E. Increases length and girth of plant body

          F. Forms cells that become organized into Secondary
             Meristems

          G. Components

               1. Protoderm -> Epidermis

               2. Procambium -> Primary Vasculature +
                                Vascular Cambium

               3. Ground Meristem -> Cortex + Pith

               4. Leaf Primordia in SAM (Superficial)

               5. Root Cap in RAM (Internal)<


     II. Secondary Growth

          A. Vascular Cambium 

               1. Origin

                    a. From procambium between xylem and phloem
                       + parenchyma between vascular bundles
                         in STEMS

                    b. From pericyle in ROOTS

               2. Two types of cells

                    a. Fusiform Initials (elongated) ->
                       axial elements = vertical conduction

                    b. Ray Initials (isodiametric) ->
                       ray parenchyma = radial conduction

               3. Direction of cell differentiation

                    a. Secondary Xylem to inside of VC accumulates
                       in annual growth rings


                    b. Secondary Phloem to outside of VC and inside 
                       older secondary phloem and periderm is     
                       crushed and is eventually lost via periderm

                    c. Vascular Cambium is perpetuated via
                       tangential cell divisions & expansion to
                       maintain VC continuity through time
     
               4.  Secondary Xylem and Phloem provide physical    
                   continuity between Primary Xylem and Phloem of 
                   Roots and Stems

               5.  Only increases girth of plant body

          B. Cork Cambium 

               1. Origin is discontinuous in space and time

                    a.  New CC made each year to inside of old CC

                    b.  Initial CC derived from Epidermis or      
                        Cortex

                    c.  Subsequent CC derived from parenchyma in 
                        Primary and Secondary Phloem

               2. CC makes Cork Cells toward outside

               3. Because of discontinuity Periderm (Bark) can    
                  include:

                    a. Epidermis + Cortex
                    b. Non Functional Primary Phloem
                    c. Non Functional Secondary Phloem

               4. Can be sloughed off, or accumulated into thick  
                  ridges & furrows

               5. Special regions of loose cork cells (Lenticels) 
                  are produced to facilitate gaseous exchange from
                  atmosphere to internal living cells.