WOOD 280

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WOOD 280 Wood Anatomy and Identification Dr.
Simon Ellis
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(No Transcript)
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(Ellis)
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Tree trunk showing the successive concentric
layers
Outer bark - dead tissue that protects the inner
tissues from drying out, from mechanical injury
and from insects Inner bark (phloem) conducts
sugars produced by photosynthesis to the roots
and other non-synthetic parts of the tree Cambium
produces secondary xylem and secondary
phloem Sapwood consists of xylem tissues
through which water and minerals move from the
soil to the leaves and other living parts of the
tree Heartwood composed entirely of dead cells,
supporting column of the mature tree
(St. Regis Paper Company)
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Sapwood - Heartwood
Sapwood Heartwood
(Hoadley)
(Core, Côté Day)
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earlywood
latewood
(Hoadley)
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(Haygreen and Bowyer)
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Three-dimensional representation of the vascular
cambium
(Haygreen and Bowyer)
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Cambial cell division
(Haygreen and Bowyer)
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Ontogeny of youngtree stem
c cortex d epidermis e epidermis pc procambium
p pith pp primary phloem px primary
xylem vc vascular cambium sp secondary
phloem sx secondary xylem
(Panshin and de Zeeuw)
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Cell development at apical shoot
Epidermis
Protoderm
Primary phloem
Secondary phloem
Apical initials
Mother cells
Procambium
Vascular cambium
Primary xylem
Secondary xylem
Cortex
Ground meristem
Pith
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Representation of developing stem
(Haygreen and Bowyer)
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Portion of a transverse section of a young stem
showing arrangement of tissues

1. Mature xylem
2. Zone of xylem differentiation
3. Cambial zone
4. Zone of phloem differentiation
5. Mature phloem

1 2 3
4 5
(Zimmerman and Brown)
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Periclinal division of cambial fusiform initials
(Haygreen and Bowyer)
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Anticlinal division of cambial fusiform initials
(Panshin and de Zeeuw)
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Formation of new ray initials in the vascular
cambium
(a) (b) (c) (d)
(e) (f)

• (a) Initial a with extensive ray contact
  survives, while initial b with sparse ray contact
  matures into a deformed cell and disappears
• A ray is split by instrusive growth of a fusiform
  initial
• A new ray initial arising from pinching off the
  top of a fusiform initial
• Two single ray cells are formed through reduction
  of a short fusiform initial either or both of
  these cells may survive and later develop into
  rays consisting of a number of cells formed by
  subsequent division of these initials or they may
  be eliminated
• A new ray is formed by septation of the entire
  short fusiform initial
• A new ray initial is formed on the side of a
  fusiform initial, which will continue to function
  as such

(Panshin and de Zeeuw)
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Plant Hormones nature, occurrence and effects
Hormone Chemical Nature Sites of Biosynthesis Transport Primary Effects
Auxins Indole-3-acetic acid Apical bud Cell to cell, unidirectional (down) Apical dominance promotion of cambial activity
Cytokinin Phenyl urea compounds Roots tips Via xylem from roots to shoots Cell division, delay of leaf senescence
Gibberellins Gibberellic acid Young tissues of shoot and developing seeds Via xylem and phloem Hyperelongation of shoots, induction of seed germination
Ethylene Ethylene Most tissues in response to stress, during senescence or ripening By diffusion from its site of synthesis Fruit ripening, leaf and flower senescence
Abscisic acid Synthesized from mevalonic acid Mature leaves in response to water stress Via the phloem Stomatal closure, induction of photosynthate transport
(Raven, Evert Eichorn)
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Plant Growth Hormones