Tree Growth and Wood Formation

• Basic macroanatomy of a tree stem

• How a tree grows

FW1035Lecture 1Bowyer et al, Chapter 1

Coast RedwoodSequoia sempervirens

Tallest Living Individual: 380 feet (~2000 yo)

Weight: up to ~2.7 million lbs

Saturn V RocketHeight: 383 feetWeight: 6.7 million lbs

Mountain AshEucalyptus regnans

Tallest Living Individual: 330 feet (~400 yo)

“World’s tallest flowering plant.”

Planes-of-View in Wood Samples

TangentialPlane

Transverse Plane (Cross-Section)

RadialPlane

Heartwood

Sapwood

Stem Macroanatomyand Transverse Anatomical Directions

RadialTangential

Vascular Cambium

Longitudinal Direction is perpendicular to the transverse directions.

Heartwood

Sapwood

Stem Macroanatomyand Transverse Anatomical Directions

RadialTangential

Vascular Cambium

Longitudinal Direction is perpendicular to the transverse directions.

Basic Wood Anatomy

Softwood Hardwood

Microanatomy

Annual Ring

An Electron Photomicrograph of Sugar Maple

Pore

Ray

Ray

Light Photomicrograph of Sugar Maple

RayPore

Annual Ring

Rays in Wood

• Ray cells are elongated in the radial direction

• Width, height, density, and appearance vary - useful for ID

Annual Ring

Latewood

Earlywood

Function: Transport from the phloem towards the pith.

Major Tissues in the Tree Stem

Outer Bark• Protection

Phloem (Inner Bark)• Transport (down)

Cambium• Radial growth

Xylem (Wood)• Transport (up) and

mechanical support

Transport in Trees

Sap - a water solution of sugars, minerals, O2, and growth regulators

• Roots – water, dissolved minerals, other nutrient uptake

• Xylem - flow up toward leaves

• Phloem - downward flow (sugars

and regulators) • Rays - flow towards the center of

the tree (pith)

Growth Tissues - “Meristematic Tissues”

Diameter• Diameter growth occurs at

the lateral meristem (vascular cambium)

• Tissues formed are “secondary tissues”

– secondary xylem

– secondary phloem

Height• Height growth and branch

shoot elongation occurs only at their tips

• Apical meristem

• Apical meristems only produce “primary tissues”

– primary xylem

– primary phloem

Meristem = Plant tissue which contains cells that have the capacity to divide to make new cells.

The Apical Meristem

The Apical Meristem

Epidermis• single layer of thick, waxy cells

that prevents moisture loss

Procambium• meristematic region that provides

growth• cell division produces primary

phloem and xylem• further differentiation gives rise to

the vascular cambium• primary xylem and pith is different

from secondary xylem (wood)

Vascular Cambium

The Vascular CambiumLateral meristematic region • Division of cells here produces

secondary xylem and secondary phloem tissues

• Diameter expansion forces tangential elongation of phloem cells

• Epidermis and primary phloem layers eventually fall off

• Dead phloem cells compose the outer bark

Vascular Cambium Two Cell Types • Fusiform Initials - divide to

produce new xylem or phloem cells that have longitudinally elongated shapes

• Ray initials - short, rounded cells that divide to produce new xylem or phloem ray cells.

Cell Division Direction

Cells can divide 2 ways:• Periclinal division - cells

divide along the longitudinal axis of the stem (responsible for diameter growth of cambium)

• Anticlinal division - cells divide in radial direction (responsible for circumference growth of tree, in general)

After Periclinal division, one cell remains a cambial initial, the other a xylem or phloem “mother” cell. Mother cells may divide several more times before differentiating into mature xylem or phloem cells, or immediately differentiate into a xylem or phloem cell without further division.

Periclinal Division

Section of a young basswood (Tilia spp.) stem

Monocot Trees (E.g. Palms) Grow Differently.