1. Tree Growth and Wood Formation
FW1035
Lecture 1
Bowyer et al, Chapter 1
Tree Growth and Wood Formation
Basic macroanatomy of a tree stem
How a tree grows

2. Coast Redwood Sequoia sempervirens
Tallest Living Individual: 380 feet (~2000 yo)
Weight: up to ~2.7 million lbs
Saturn V Rocket
Height: 383 feet
Weight: 6.7 million lbs

3. Mountain Ash Eucalyptus regnans
Tallest Living Individual: 330 feet (~400 yo)
“World’s tallest flowering plant.”

4. Planes-of-View in Wood Samples
Transverse Plane (Cross-Section)
Radial
Plane
Tangential
Plane

5. Stem Macroanatomyand Transverse Anatomical Directions
Sapwood
Heartwood
Longitudinal Direction is perpendicular to the transverse directions.
Radial
Tangential
Vascular Cambium

6. Stem Macroanatomyand Transverse Anatomical Directions
Sapwood
Heartwood
Longitudinal Direction is perpendicular to the transverse directions.
Radial
Tangential
Vascular Cambium

7. Basic Wood Anatomy
Microanatomy
Annual Ring
Softwood
Hardwood

8. An Electron Photomicrograph of Sugar Maple
Ray
Pore
Ray
An Electron Photomicrograph of Sugar Maple

9. Light Photomicrograph of Sugar Maple
Pore
Ray
Annual Ring
Light Photomicrograph of Sugar Maple

10. Rays in Wood Function: Transport from the phloem towards the pith.
Ray cells are elongated in the radial direction
Width, height, density, and appearance vary - useful for ID
Annual Ring
Latewood
Earlywood

11. Major Tissues in the Tree Stem
Outer Bark
Protection
Phloem (Inner Bark)
Transport (down)
Cambium
Radial growth
Xylem (Wood)
Transport (up) and mechanical support

12. 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)

13. Growth Tissues - “Meristematic Tissues”
Height
Height growth and branch shoot elongation occurs only at their tips
Apical meristem
Apical meristems only produce “primary tissues”
primary xylem
primary phloem
Diameter
Diameter growth occurs at the lateral meristem (vascular cambium)
Tissues formed are “secondary tissues”
secondary xylem
secondary phloem
Meristem = Plant tissue which contains cells that have the capacity to divide to make new cells.

14. The Apical Meristem

15. The Apical Meristem Epidermis Procambium
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)

16. Vascular Cambium The Vascular Cambium Lateral 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

17. 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.

18. 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)

19. Periclinal Division
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.

20. Section of a young basswood (Tilia spp.) stem

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