WOOD 280 – Tree growth and wood formation

Softwoods Hardwoods (gymnosperms) (angiosperms) Lodgepole pine Hemlock Aspen Oak Douglas-fir Spruce Birch Maple (Waddington arboretum)

May 3 May 21 October 11 December 20 (Ellis)

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* Tree trunk showing the successive concentric layers Outer bark Sapwood Heartwood Cambium Inner bark 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)

Sapwood - Heartwood Sapwood Heartwood Sapwood Heartwood (Hoadley) (r.fld.czu.cz)

earlywood latewood (Hoadley)

(Haygreen and Bowyer)

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

Cambial cell division Fusiform initials

Apical vs. Lateral Meristems

* Ontogeny of young tree stem c cortex d epidermis e endodermis vc Ontogeny of young tree stem c cortex d epidermis e endodermis pc procambium p pith pp primary phloem px primary xylem vc vascular cambium sp secondary phloem sx secondary xylem (Panshin and de Zeeuw)

Cell development at apical shoot Protoderm Epidermis Primary phloem Secondary phloem Apical initials Mother cells Vascular cambium Procambium Primary xylem Secondary xylem Cortex Ground meristem Pith

Representation of developing stem (Haygreen and Bowyer)

* Portion of a transverse section of a young stem showing arrangement of tissues (Zimmerman and Brown) Mature xylem Zone of xylem differentiation Cambial zone Zone of phloem differentiation Mature phloem 1 2 3 4 5

Cell types and tissues associated with cambial activity

Periclinal division of cambial fusiform initials (Haygreen and Bowyer)

Softwood – longitudinal section (tangential) Longitudinal parenchyma Ray Longitudinal tracheids

Anticlinal division of cambial fusiform initials (Panshin and de Zeeuw)

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)

Plant Hormones – nature, occurrence and effects 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 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)

Plant Growth Hormones