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					Simplified Plant Tissues
    Lesson Plan 4
       00hblp4v1
               Plant Organs
   The 3 primary organs found in plants are:
    • Leaves
    • Stems
    • Roots
   Since flowers are thought to have evolved
    from leaves, they are called “reproductive
    structures”.
   Leaves, stems, roots, and flowers are all
    made up of various tissues.
                Plant Tissues
   Plant Tissues fall into two large categories:

    • Meristematic, or

    • Permanent (Non-Meristematic)
          Meristematic Tissues
   Meristems are places in plants where cell
    division is occurring.
   During cell division, one cell becomes two
    cells. Each new cell can also divide.
          Meristematic Tissues
   In this class we will discuss three kinds of
    meristems:
       • Apical Meristems
       • Intercalary Meristems
       • Lateral Meristems
               Apical Meristems
 In plants belonging to
  the DICOT class,
  apical meristems are
  located in BOTH the
  shoot tips and root tips.
  A shoot is simply a
  young, leaf-bearing
  stem.
                              Microscopic View of an
 In plants belonging to
                                 Apical Meristem
  the MONOCOT class,
  apical meristems are
  located ONLY in the
  root tips.
             Apical Meristems

 Apical meristems
  cause PRIMARY
  GROWTH.
 As cells in apical
  meristems divide and
  elongate, shoot tips
  and root tips grow
  longer. This increase
  in length is called
  primary growth.
                          Apical Meristem in
                              a Root Tip
Apical Meristems
•Primary growth of shoots
and roots occurs as the cells
of the apical meristem divide
and elongate.
           Apical Meristems
 A bud is a dormant
  apical meristem.
 When conditions are
  favorable for growth,
  buds “break” and
  begin pushing out new
  growth.


                          Bud Break
                      Buds
   Buds come in 3 basic types:
    • Vegetative-produce stems and leaves.
    • Flower-produce only flowers.
    • Mixed-produce stems/leaves and flowers.
           Mixed Buds




Mixed buds of Amelanchier x grandiflora
Mixed Buds of Cornus alternifolia



           1                 2




            3                4
             Pussy Willow
                     Pussy Willow is a plant
                     which bears separate
                     vegetative and flower
                     buds. In the image to the
                     left you can see vegetative
                     buds producing green
vegetative           leaves and flower buds
   bud
                     producing male flowers
                     (the species is dioecious).
flower bud
                     Also, note that the two
                     different types of buds are
                     indistinguishable from
                     one another.
   Lantanaphyllum Viburnum




flower bud                   vegetative bud

Viburnum x rhytidophylloides, Lantanaphyllum Viburnum,
also bears separate vegetative and flower buds. However,
the two types of buds are distinctly different from one
another in appearance.
         Intercalary Meristems
   In addition to the apical meristems located
    in their root tips, plants in the MONOCOT
    class have special meristems called
    intercalary meristems.
   Intercalary meristems are located on
    monocots where the leaf bases connect to
    the stem of the plant.
 Intercalary Meristems




Monocots, like grasses, have intercalary
meristems which allow the leaves to grow
          back after mowing.
             Lateral Meristems
 In addition to the
  apical meristems
  located in the shoot
  and root tips, plants in
  the DICOT class have
  lateral meristems.
 Lateral meristems
  cause SECONDARY
  GROWTH.
                             Lateral Meristems cause an
 Secondary growth
                              increase in stem diameter
  causes stems and
  roots to grow larger in
  diameter.
Lateral Meristems

    Think of a lateral meristem
    as being a cylinder, several
    cell layers thick, of
    actively dividing cells.
            Lateral Meristems
   MONOCOTS do not have lateral
    meristems.
   Lateral meristems come in two basic types:
    Vascular cambium; meristematic tissue
    located between the xylem and phloem. The
    vascular cambium makes new xylem and
    phloem cells.
   Cork cambium; meristematic tissue located
    just below the bark in woody dicot stems.
    The cork cambium makes new bark cells.
          Lateral Meristems
                     Phloem


                     Vascular Cambium



Cross Section of a   Xylem (Wood)
Woody Dicot Stem
         Lateral Meristems
                   Cork (Bark)

                   Cork Cambium



                   Vascular Cambium




Woody Dicot Stem
              Permanent Tissues
 Permanent tissues are non-meristematic.
 The following permanent tissues will be
  discussed:
    •   epidermis
    •   xylem
    •   phloem
    •   cortex
    •   pith
    •   fibers
                   Epidermis
 The epidermis can be
  from one to several
  cell layers thick.
 It covers all the parts
  of a plant; shoots,
  stems, leaves, and
  roots.
                            Agave Epidermis
 In woody dicots the
  epidermis is called the
  bark or cork.
                   Epidermis
 The epidermis
  covering the leaves of
  plants contains
  thousands of tiny pores
  called stomata. The
  singular of stomata is
  stoma.
 Stomata are usually
  found on the underside
  of leaves.
 An apple leaf contains
                            Stoma in Fuchsia
  39,000 stomata per
  square centimeter!
                   Epidermis
                             Cuticle
 In most plants the cells
  of the upper and lower
  leaf epidermis secrete
  a waxy substance that
  covers the leaf and
  prevents water loss.
 This waxy secretion is
  called a cuticle.           Leaf with Cuticle
                  Epidermis

 In many plants, the cells of
  the upper and lower leaf
  epidermis are modified to
  form small hairs.
 These small hairs are called
  pubescence.
 Lambs Ear is an example of
  a herbaceous perennial that
  has pubescent leaves.
                                 Leaf Hair
                 Cortex
   The cortex is a tissue found in both the
    stems and roots of monocots and dicots.
   The cortex is made up of thin-walled cells.
   Vascular bundles are surrounded by the
    cortex.
Cortex
Vascular Bundles




   Dicot Stem      Monocot Stem
    Dicots-Cortex and Pith

                          In this dicot stem cross
                           section the cortex,
                           vascular bundles, and
                           pith have been
                           identified.
                          The pith is located in
                           the center of dicot
                           stems.
     Cortex       Pith
Vascular Bundle
         Monocots-Cortex
                            In this monocot stem
                             cross section the
                             cortex and vascular
                             bundles have been
                             identified.
                            Monocots do not have
                             a pith.


Cortex   Vascular Bundle
                      Xylem
                       
                       Xylem tissue conducts water
                       and dissolved mineral
                       nutrients.
                      It is composed of columns
                       of vessel cells (tracheids in
                       gymnosperms), stacked one
                       upon another, and fibers.
                      Vessel cell walls are pitted
                       and allow water passage
                       between the xylem and
                       surrounding tissues. Mature
Xylem         Phloem   xylem cells are dead.
   fibers not shown
                      Phloem
                           Phloem tissue conducts the
                            food produced by the leaves in
                            a downwards direction to
                            stems and roots (from source
                            to sink).
                           Phloem is composed of sieve
                            tubes, companion cells, and
                            fibers.
                           The end walls of the sieve
                            tubes are called sieve plates.

Xylem         Phloem
   fibers not shown
                      Fibers
                             Fiber cells have thick
                              walls. A cluster of
                              fiber cells is called a
                              fiber.
                             Fibers are associated
                              with the xylem and
                              phloem of both
 Fiber Cell - the cell        monocots and dicots.
wall is stained dark red.    Fibers provide
                              strength and support to
                              xylem and phloem.
           Fibers




A cluster of many fiber cells
      make up a fiber
                      Fibers

                            Phloem
                         Xylem

                          Cortex

                                 Fibers




Vascular Bundles in
       Corn
The End

				
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