Lecture 6 stem by HC120809085953

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									Lecture 6:


Stems
The axes of plants—consist of nodes (where leaves and
axillary buds are produced) separated by internodes.
               Morphology of the shoot apex

                                                      Apical meristem


                                            Leaf primordium



                                           Axyllary bud primordium


                                            Leaf primordium (older)



                                            Axyllary bud primordium


Shoot growth in Rubus spp:
http://www.youtube.com/watch?v=aNjR4rVA8to&feature=PlayList&p=68A23A31F29AB1
9F&playnext=1&playnext_from=PL&index=28
Structure of stem apex
            Anatomy: roots versus stems

         Roots                                     Stems

-Epidermis with absorbent hairs      -Epidermis with glandular and/or
                                     nonglandular trichomes, and
-Thin or absent cuticle              stomata
-Xylem and phloem do not associate   -Cuticle present
to form bundles
                                     -Xylem and phloem form bundles
- Development of xylem is exarch     (closed or open)
                                     -Development of xylem is endarch
Anatomy of stems: Vascular bundles in the stem have both xylem and
phloem
                    Monocots versus “Dicots”




                                   Vascular bundles

Transversal sections: monocot                   “Dicot”
Monocots have only a primary structure




                phloem       Closed collateral
                             bundle [“closed”
                xylem        because no cambium
                             differentiates]




                          Mx (at the exterior)
                          Px (at the interior)
                   ‘Dicots’ develop a secondary structure
                        Intrafascicular
                        vascular cambium

Interfascicular                                              Open collateral
vascular cambium                   phloem
                                                             bundle [“open”
                                                             because
                                     v. cambium              intrafascicular
                                                             cambium
                                   xylem                     differentiates
                                                             between primary
                                                             phloem and xylem]
                    Intrafascicular + interfascicular cambium = vascular cambium


                                                                   phloem

                                                                  v. cambium

                                                                   xylem
                         Anatomy of stems
                         Monocots versus “Dicots”



- Vascular bundles are scattered in a   - Vascular bundles arranged in a
the ground tissue.                      distinct circle.



- They do not develop a vascular        - They develop a secondary
cambium and cork cambium                structure: the vascular cambium and
differentiate, therefore they don’t     cork cambium differentiate.
have a secondary structure – at
least not one in the sense of dicots.
Secondary structure in herbaceous ‘dicots’




                                 Vascular cambium
       Fibers                  produces relatively little
 Sph
                                secondary xylem and
                             stems remain herbaceous.
                              Stems will be destroyed
  Sx                             during the winter.

                                Sph = secondary phloem
                                  Sx = secondary xylem
              Secondary structure in woody ‘dicots’
              Vascular cambium produces more secondary xylem




                                                                  Periderm

                                                                 Vascular cambium


                                                               Secondary phloem
                                                             produced in the 1st year

                                                              Secondary xylem
                                                             produced in the 1st
                                                                   year




Example, Sambucus spp., transversal sect., 1-year old stem
          Secondary structure in woody ‘dicots’

                                                       phloem
                                                 Vascular cambium
                                                  3rd year’s xylem


                                                 2nd year’s xylem




                                                  1st year’s xylem




                     pith

Example, Tulip tree (Lyriodendron tulipifera), transversal sect.
Heartwood and sapwood
Each wood is unique!
   Xylem uses:
Dendrochronology
Dendroclimatology
Dendroarchaeology
 Dendroforensics
The secret of Stradivarius (1644 –1737)
The Bark: the succession of periderms produced
  cork cambia during the life of a woody plant.




                                Bark patterns are unique for
                                       each species
E.g. Birch tree – Betula papyrifera




                                 Inuit snow-
                                   glasses
Precious bark, e.g. Cinchona tree - quinine
Specialized (modified) stems – 1) Rhizomes




            Iris sp.


                               Reeds, Phragmites australis




 Ginger, Zingiber officinale
        2) Runners and stolons




Stolon – under the     Runners - above the
ground                 ground
3) Tubers




       Potato: Solanum
       tuberosum
The Great Irish Potato Famine (1880-1850)




                     Phytophtora infestans
                     Potato blight
                           4) Bulbs




                  Advenititious
                     roots




E.g. onion, tulip, etc.               e.g. Lilies, garlic, etc.
Tulipomania


      • Tulips caused the first
        “stock market” crush in
        the history of
        humankind in 16th
        Netherlands.
      • The whole nation
        caught up in bulb
        trading frenzy
The value of a tulip bulb

                   “Four oxen or
                 Twelve sheep or
                24 tons of wheat or
              2 hogsheads of wine or
                 2 tons of butter or
                4 barrels of beer or
             1000 pounds of cheese or
              A silver drinking cup or
                       even a
                       A ship”
             5) Corm




Crocus sp.             Gladiolus sp.
6) Cladophylls e.g. Opuntia spp.
“Nopales” in Mexico – Opuntia ficus indica
      7) Succulent stems




Cactaceae             Euphorbiaceae
                   8) Stems with spines




Honey locust - Gleditsia triacanthos


                                       Ziziphus spina-christi
Symbiosis between Acacia cornigera and Psudomyrmex ants




                        http://www.youtube.com/watch?v=RoKlA1h6cfU

								
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