I.  DEPOSITION OCCURS DURING CELL EXPANSION

    A.  All types of cells
        
    B.  Extra thick primary cell walls

        1.  Hypothesis 1

        2.  Hypothesis 2

SECONDARY CELL WALL DEVELOPMENT

I.  DEPOSITION OCCURS AFTER CELL EXPANSION

    A.  Basic Model

    B.  Pit development
 
         1.  Ray Parenchyma

        2.  Axial Parenchyma

        3.  Fibers

        4.  Fiber-Tracheids

        5.  Tracheids
 
            a. Angiosperm

            b. Gymnosperm