Wood Anatomy of Tree RingsWood Anatomy of Tree Rings

Tree growth begins with photosynthesis to produce new wood when the growing season begins.

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.

Like “melting wax” !!

Like “melting wax” !!

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.

STEM ANALYSIS

Locally Absent Rings

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

False Ring

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

Viewing wood: tangential, radial, and transverse planes. We are only interested in which of these?

Definitions:

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 externalenvironment 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.

Note the five major portions of the tree trunk.

Phloem (inner bark)

Xylem (wood)

Cambium

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