Periderm

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Periderm

  1. 1. 2/17/2010 1 xylem  No change; living cells die Pith No change; ; living cells die 1 phloem Compressed Cortex Removed or retained Epidermis Removed or retained Leaf gap Cambium develops (closing) Protective tissue in  replacement of the  epidermis Consists of : Phellogen/ cork cambium Phellem/ cork Phelloderm / secondary  cortex Secondary meristem Lateral meristem One type of initials Appear rectangular in xs (regular polygons) l l l Vacuolated May contain chloroplasts and tannins No intercellular spaces 1
  2. 2. 2/17/2010 Legend: 1 lenticel 3 cork Polygonal in TS and XS 4 cambium 5 collenchyma Compact radial rows  7 phloem 8 secondary xylem y y Devoid of intercellular spaces 9 primary xylem Dead cells 2 epidermis 6 sclerenchyma Lined with a layer of suberin 10 pith SUBERIN‐ impermeable to water and gases;  withstands actions of acids Phelloids= non suberized Living cells; non suberized Arranged in radial rows ORIGIN Similar to cortical parenchyma  Epidermal cells Subepidermal Parenchyma and Collenchyma Parenchyma of phloem or pericycle, phloem rays Lose their  Volume of  Undergo  Starch grains  Cells become  central  cytoplasm  periclinal and tannins  meristematic vacuole increases division are lost Number of phellem layers > phelloderm layers Epidermis – Nerium Immediately below the epidermis 2nd or 3rd cortical layers – Aristolochia Near the phloem or in phloem parenchyma h hl hl h Roots – pericycle (dicot; gymnos); outer  layers of cortex (monocot) *first phellogen 2
  3. 3. 2/17/2010 Deeper in the cortex or primary phloem or  deeper within secondary phloem Types Form entire cylinders (CC formed from inner  layers) Form of scales or shells (CC formed  in the  epidermis) Tissues external to innermost phellogen Usually dead Cork, cortical, phloem tissues INNER BARK Living part 3
  4. 4. 2/17/2010 Depends on the  manner of growth of  periderm, structure of  phellem, etc phellem  etc Determined by the  type of rhytidome A. Scaly bark B. Ring bark Suberized cortical cells (when epidermis is  sloughed off) e.g. Gramineae Storied cork –derived from the outer cortex e.g palms ‐ repeated division of cortical parenchyma  cells and subsequent suberization of the  products of division  ‐ without formation of an initial layer, or  phellogen. Formed in the pericycle of the root or  underground stem of certain families Formed by a special phellogen ‐‐[centrifugal prod.]‐‐Layers of thin‐walled  f l d f h ll d non‐suberized cells alternating with a layer of  endodermal‐like cells Endodermal‐like cells become cork Cork cells are living and may serve as storage 4
  5. 5. 2/17/2010 Restricted areas of relatively loosely arranged  cells [suberized or non‐suberized] May develop a. under a stoma b. group of stoma c. between stomata [if sparsely distributed] b f l d b d d. under some stoma [if numerous] May appear in longitudinal rows or horizontal  rows • Division progresses in the cortex  • Periderm formation or shortly before – inwards dependent on the persistence of epidermis • Orientation of divisions becomes  • Cells under stoma or group of stomata  more periclinal begin to divide in different directions • Lenticel phellogen is formed • Chlorophyll disappears COMPLEMENTARY CELLS 5
  6. 6. 2/17/2010 • Inc. in number of complementary  cells May be suberized or non‐suberized More or less spherical • Rupture of epidermis Thin‐walled *Lenticel phellogen—may produced  • Complementary cells are pushed  phelloderm below out and rise above the organ * CLOSING LAYERS– compact tissue, alternate  with complementary cells Closing layer Complementary cells Origin‐‐ Epidermis 6

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