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Wood Anatomy of Tree Rings. Tree growth begins with photosynthesis to produce new wood when the growing season begins. Like “melting wax” !!. Trees grow upward and outward (including root tips), but….

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Like “melting wax” !!

Trees grow upward and outward (including root tips), but…

… tree growth actually begins in the crown and moves downward due to the growth regulator, auxin.


Meristems: apical and lateral growth

D: cell division

E: cell elongation

M: cell maturation


Meristems: annual growth can also be seen in the branching patterns of many tree species (esp. conifers)


When we dissect the trunk, we can see this annual incremental growth, both upward and outward.


locally absent rings
Locally Absent Rings

Rings may be locally absent along the length of the tree.

false ring
False Ring

Cells leading into the false ring will gradually decrease in size and then gradually increase back to earlywood cells.



Cambium: the growing (generative) layer between the xylem and phloem.

Xylem: principle strengthening and water conducting tissue of the stem, roots, and branches.

Phloem: inner bark, principal function to distribute manufactured foodstuffs.

Bark: dead, outer tissue that protects the cambium from the external

environment and exposure to pathogens and physical injury.

Vessel: the composite, tube-like structure found in hardwoods from the fusion of cells in a longitudinal column.

Fiber: an elongated cell with pointed ends and a thick or infrequently thin wall.

Rays: ribbon-shaped tissue extending in a radial direction across the grain of the wood.


Phloem (inner bark)


Xylem (wood)


Role of heartwood is…?

Role of sapwood is…?


The Wood Cell:

1. Holocellulose

a. alpha-cellulose (40-50%) = non-soluble = long-chain polymers (glucose)

b. hemicellulose (20-35%) = readily soluble = short-chain polysaccharides

2. Lignin (15-35%) – non-carbohydrate materials in cell wall, very complex chemical structure.

3. Numerous Extractives – can be removed!

a. tannins

b. oils and resins

c. other complex organic compounds


Cell lumen

Cell wall