1. Wood with no living cells.
HEARTWOOD
Wood with no living cells.
Hoadley: “The central core of wood in mature stems that was at one time sapwood but no longer conducts sap or has living cells.
In most species, infiltration of extractives imparts a perceptibly darker color to this wood.”

2. Some species have light-colored heartwood
NOT ALL HEARTWOOD
HAS A DARKER COLOR
THAN THE SAPWOOD
Some species have light-colored heartwood
Spruce (Picea)
Aspen (Populus)

3. The number of sapwood rings varies with species.
Catalpa
Walnut Oaks
S. Yellow Pine Tupelo
Ponderosa Pine
Most ring porous species have 10 or fewer rings of sapwood

4. Changes Sapwood to Heartwood
Nuclei in parenchyma cells degenerate
Decrease in nitrogenous materials
Moisture content changes
Decrease in starch
Accumulation of extractives
These changes can be “abrupt” or gradual.

5. Death of the Parenchyma Cell
Spatial control -- Distance from the cambium & secondary phloem
Temporal Control -- Age of the parenchyma cell (programmed to die after a certain age).
Which factor is most important varies from species to species, and can be a combination of the two.

6. EXTRACTIVES
Organic compounds (e.g, gums, tannins, oils) manufactured by the parenchyma cells.
Extractives can be removed (extracted) by water, alcohol, or other solvents

7. EXTRACTIVES Not “structural elements” of cell walls
May or may not be colored
May be in the cell walls or in cell lumens

8. Heartwood Properties If extractives go into the cell wall,
If a lot of extractives deposited in cell wall,
Then may be some increase in the compressive strength of the heartwood relative to “like-aged” sapwood.

9. Effects of Extractives
Some, not all extractives are toxic to decay organisms or insects. Heartwood then will be more durable, last longer than sapwood.
This may be heartwood gets considered “stronger” than sapwood -- in some species it lasts longer.

10. Extractive Effects If extractives coat cell wall and pit membranes,
Then will reduce permeability.
Sapwood Intervessel Pit
Heartwood Intervessel Pits

11. Undesirable Effects of Extractives
Increased chemical consumption for pulping and bleaching
Tannins can corrode metals
Can interfere with setting of paints, glues, and varnishes
Can migrate during drying cause discoloration.

12. Desirable Effects of Extractives
Color
Durability
Dimensional Stability

13. Is Heartwood Stronger
than Sapwood?

14. More Cell Wall Substance
Does Heartwood Have
More Cell Wall Substance
Than Sapwood?