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									Meristems and plant structure
The plant body

Tissue systems

Meristems

Stems

Roots

Secondary thickening
                           shoot tip
                           (terminal bud)
        lateral                                young leaf
        (axillary)
                                               flower
        bud

            node
                     internode
                                               EPIDERMIS
           node
                                                                Dermal tissue
                                            leaf
VASCULAR TISSUES
                                               seeds
                                               (inside             The plant body
                                               fruit)
 GROUND TISSUES                                withered
                                               cotyledon
    SHOOT SYSTEM
     ROOT SYSTEM
                                                                    A tomato plant
   primary root
                                                   root hairs
     lateral root
                                               root tip
                                               root cap
                      Tissues
A   tissue is a cooperative unit of many similar cells
      performing a specific function
      within a multicellular organism

Tissues usually have cells that are specialized for
particular functions

The vascular tissue system conducts water and
nutrients from roots to leaves through specialized cells
and conducts the products of photosynthesis, sugars,
from leaves in different but equally specialized cells.
                                There is continuity of tissue
                                 systems through the plant




                            Cells conduct water and nutrients
                            and products of photosynthesis




Cells protect the plant   The body of the plant. Tissues with
                          different functions: ee.g., storage, support
           activity at           Shoot apical meristem
           meristems               Actively dividing cells near the
                                   dome-shaped tip
           new cells
           elongate and start
           to differentiate
           into primary
           tissues                The apical meristems
                                  descendants divide, grow and
                                  differentiate to form:
                                        Protoderm
                                        Ground meristem
       new cells elongate and           Procambium
       start to differentiate
       into primary tissues


           activity at
           meristems               Root apical meristem
Root cap      Function of apical meristems         Fig. 29.4 p501
                                       Immature leaf
shoot apical meristem


       procambrium

       protoderm    procambrium ground meristem
                                                                 Fig. 29.11, p. 504




               Meristems-> Tissues                         Meristems




                                                                Tissues



      cortex procambrium           primary xylem       primary pholem
                            pith
            What does a meristem look like?
  Coleus
                                Apical meristem




                               Transverse section through the
Longitudinal section through   apical meristem and newly forming
the apical meristem            leaves
                Scanning electron microscope picture
                  of Myriophyllum apical meristem

                                                The apical
            Scanning                            dome is usually
            electron                            convex or flat,
            microsco                            as in this
               pe                               example, and
             picture                            its surface is
                                                smooth.

                                                Developing
                                                leaves cover
                                                the apex

                                                Most recently
Water-milfoil                                   budded leaves
         Coleus



  Axilliary bud meristem


The axilliary meristem may
develop into a foliated branch.
Do roots grow differently to shoots?


          What is their problem?



            What may it affect?



  Is anything easier for roots rather than shoots?
Root meristem and
    structure

Roots must ‘force’ their
way through the soil

Protection of the apical
mersitem

Delayed initiation of the
lateral meristems (not
shown in diagram)

Different requirements for
support and water
collection and distribution
Zea mays root
    apex

                Zea mays root apex
                showing the junction
                between root apex
                and the root cap
Lateral root development in
         Zea mays

A meristem develops from parenchyma
and the lateral root grows out through
the cortex
Which is the most important function of a tree trunk:



               support of branches and foliage,


               conducting water, nutrients and sugars?




How might you find out?
                      Stem thickening
Lateral meristems
  Two lateral meristems in older stems and roots of woody
  plants produce secondary growth that results in an
  increase in diameter (whereas apical meristems result in an
  increase in length).
Vascular cambium            secondary vascular tissues, xylem phloem
Cork cambium             periderm (replaces the epidermis), bark tissue
                                                                   secondary
                                                                   xylem
                          Bark


                   cork cambrium

                 vascular cambrium


                                                     thickening    secondary
                                                                   phloem
Secondary growth
             Cell divisions of the cambium
Cambium cells in yellow                         outer surface
                                                of stem or root


                                              Phloem
                                             production


  division    division


                           Xylem
                         production



                                      direction of radial growth


                                                   Fig. 29.22, p. 511
Fig. 29.8, p. 502

pit in cell wall
                        Cells of vascular tissue
                                 one vessel member
                                                                     sieve plate




                                                          Sugar
                    cytoplasm
                                                        transport
                    absent
                    (cells
                    dead at                          sieve-tube
                    maturity                          member
                                                     companion
                                                     cell (living)

                      Water
                    conduction                                         PHLOEM
TRACHEIDS                           VESSEL                           SIEVE TUBE
             Transverse section of Quercus rubra wood

                                         vessel




                                                    EARLY WOOD



                                                    LATE WOOD


                                                    toward stem
                                                    surface
Fig. 29.25, p. 513
        Taking sections through a stem




Transverse        Radial           Tangential
 Section        Longitudinal      Longitudinal
                  Section           Section



                                      Fig. 29.3, p. 501

								
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