1&2 growth

PRIMARY AND SECONDARY PLANT GROWTH

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.