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WOOD 280

Wood Anatomy and IdentificationDr. Simon Ellis

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Lodgepole pine Hemlock

Douglas-fir Spruce

Softwoods

Aspen Oak

Birch Maple

Hardwoods

(Waddington arboretum)

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May 3 May 21

October 11 December 20

(Ellis)

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*

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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)

*Outer bark

SapwoodHeartwood

Cambium

Inner bark

Outer bark

Sapwood

Heartwood

Cambium

Inner bark

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Sapwood - Heartwood

Sapwood Heartwood

(Hoadley) (Core, Côté & Day)

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earlywood latewood

(Hoadley)

9(Haygreen and Bowyer)

Three-dimensional representation of the vascular cambium

(Haygreen and Bowyer)

Cambial cell division

11(Haygreen and Bowyer)

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c cortexd epidermise epidermispc procambiump pithpp primary phloempx primary xylemvc vascular cambiumsp secondary phloemsx secondary xylem

Ontogeny of youngtree stem

(Panshin and de Zeeuw)

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Cell development at apical shoot

Apical initials

Mother cells

Procambium

Protoderm

Ground meristem

Epidermis

Cortex

Pith

Vascular cambium

Primary xylem

Primary phloem

Secondary xylem

Secondary phloem

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Representation of developing stem

(Haygreen and Bowyer)

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1. Mature xylem2. Zone of xylem differentiation3. Cambial zone4. Zone of phloem differentiation5. Mature phloem

Portion of a transverse section of a young stem showing arrangement of tissues

(Zimmerman and Brown)1 2 3 4 5

*

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bark

mature phloem

maturing phloem

differentiating phloem radially enlarging phloem

dividing phloem (phloem mother cells)

cambium cambial initial (dividing)

dividing xylem (xylem mother cells)

differentiating xylem radially enlarging xylem

maturing xylem

mature xylem

pith

Cell types and tissues associated with cambial activity

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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(b) A ray is split by instrusive growth of a fusiform initial(c) A new ray initial arising from pinching off the top of a fusiform initial(d) 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

(e) A new ray is formed by septation of the entire short fusiform initial(f) 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