Dr. Simon Ellis
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Softwoods Hardwoods
Lodgepole pine Hemlock Aspen Oak
Douglas-fir Spruce Birch Maple
(Waddington arboretum)
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May 3
October 11
May 21
December 20
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(Ellis)

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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, C ôté & Day)
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earlywood latewood
(Hoadley) 7

(Haygreen and Bowyer)
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Three-dimensional representation of the vascular cambium
(Haygreen and Bowyer)

(Haygreen and Bowyer)
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Ontogeny of young tree stem c d e vc sp sx pc p pp px cortex epidermis epidermis procambium pith primary phloem primary xylem vascular cambium secondary phloem secondary xylem
(Panshin and de Zeeuw)
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Protoderm
Epidermis
Apical initials
Mother cells
Procambium
Primary phloem
Vascular cambium
Primary xylem
Secondary phloem
Secondary xylem
Cortex
Ground meristem
Pith

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 2 3 4 5
1. Mature xylem
2. Zone of xylem differentiation
3. Cambial zone
4. Zone of phloem differentiation
5. Mature phloem
(Zimmerman and Brown)
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Cell types and tissues associated with cambial activity bark mature phloem differentiating phloem cambium differentiating xylem maturing phloem radially enlarging phloem dividing phloem (phloem mother cells) cambial initial (dividing) dividing xylem (xylem mother cells) radially enlarging xylem maturing xylem mature xylem pith
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(Haygreen and Bowyer)
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(Panshin and de Zeeuw)
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(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
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(Panshin and de Zeeuw)

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