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UNDERSTANDING WOOD. Trees. Trees. Hardwoods and Softwoods. Gymnosperms – Class of plants having naked seeds including all softwood trees Angiosperms – Class of plants having seeds enclosed or covered. Includes all hardwood trees. Tree Cells. Living cells (protoplasm) Non living cells

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  2. Trees

  3. Trees

  4. Hardwoods and Softwoods • Gymnosperms – Class of plants having naked seeds including all softwood trees • Angiosperms – Class of plants having seeds enclosed or covered. Includes all hardwood trees

  5. Tree Cells • Living cells (protoplasm) • Non living cells • Most cells are elongated • The cell axis is oriented vertically

  6. Planes And Surfaces

  7. Cross Section

  8. Annual Rings Earlywood • Usually light in color • Usually softer than latewood Latewood • Typically darker in color • Typically has higher density Uneven Grain - Pronounced difference in earlywood and latewood (red oak) Even Grain – Little contrast between early and late wood (eastern white maple)

  9. Earlywood and Latewood

  10. Rays (Fleck or Flake) • Strips of cells extending radially within a tree and varying in height from a few cells in some species to 4 inches or more in oak. • Rays serve primarily to store food and to transport it horizontally in the tree

  11. Rays (Fleck or Flake)

  12. More About Cells Some cells are comprised of reproductive tissue. They divide and form new cells. • Apical meristematic tissue – growth tips • Lateral meristematic tissue – cambium Cells are collectively called tissue • Bark tissue • Wood tissue • Both are permanent tissue

  13. Photosynthesis • Water and nutrients move up through the roots and sap wood cells to the leaves. • Most of the water evaporates helping cool the foliage. • Water from the soil combines w/CO2 catalyzed by chlorophyll and energized by the sun produces basic sugar.

  14. Photosynthesis • Sap (sugar) is carried downward through the inner bark, distributed to the cambium layer where new cells are built.

  15. These facts are important because……. • During the primary growth season the cambium is fluid and the cell walls are extremely thin. • During the dormant season cambial cells are thick and rigid. What does this mean to woodworkers? If you were making clock faces or coasters from cross-sections would you want cross-sections harvested in the summer or winter? If you were peeling logs to build log cabins when would you want to harvest?

  16. More AboutCell Reproduction • Division of cambium cells takes place lengthwise. • Sister cells are created

  17. More About Cells New wood cells undergo a change • They develop a fixed size and shape. • They develop a secondary cell wall • Cellulose • Lignin – Comprises 25% of woods composition Most wood cells eventually loose their living protoplasm • Prosynchyma – Cells whose function is to support the tree and to conduct sap • Parenchema – A small percentage of cells found in the rays retain living protoplasm and can assimilate and store food

  18. Sapwood & Heartwood • Twigs – All sapwood • As twigs grow they no longer need all of the wood tissue to conduct sap • Near the pith sapwood cells cease to transport sap and become heartwood • As sapwood becomes heartwood, extractives are formed giving heartwood its darker color

  19. Extractives In Heartwood • Formed in cell walls • Give heartwood a distinctive brown, red color • There are exceptions – Spruce extractives are non pigmented • Properties of Extractives • Fungal and decay resistance • Make wood impermeable (acts as a preservative) • Make wood denser • Makes wood more stable • Can be abrasive • Causes surface hardness

  20. More About Heartwood • As the tree’s girth increases a proportionate amount of heartwood is created as new sap wood is created. • The amount of heartwood varies from species to species and growing environment

  21. Density & Specific Gravity of Wood • Density = weight/unit volume • Specific Gravity – The ratio of the density of wood to the density of water. Example: White Ash weighs 37.44 lb./ft3 Water weighs 62.4 lb./ ft3 37.44/62.4 = 0.6

  22. So why should we care about density and specific gravity?

  23. Density and Specific Gravity • Single most important indicator of strength in wood • Hardness • Ease of machining • Nailing resistance • Generally denser wood shrinks and swells more creating greater problems in drying

  24. Resistance to Heartwood Decay

  25. Hardwood Cell Types • Vessel Elements • Relatively large in diameter • Form end to end forming continuous pipelines for sap conduction. • Fibers • Small in diameter • Closed ends and thick walls (poor for sap conduction) • Give strength to the wood

  26. Hardwood Cell Types Pores • When vessels are cut transversely (across the end grain) pores are exposed. Because all hardwoods contain vessels they are considered Porous. • Softwoods do not contain vessels therefore they are considered non-porous • The size, location and number of vessel cells determine the appearance, uniformity and hardness of a hardwood

  27. Annual Rings

  28. Porosity of Hardwoods • Ring Porous Large pores concentrate in the earlywood Pronounced uneven grain Distinct figure or pattern Typical Species – Oak, Ash, Elm and Chestnut

  29. Porosity of Hardwoods Semi Ring Porous • Large vessels in earlywood and small vessels in latewood but more evenly distributed than ring porous • More even grained • Less distinctive figure • Typical species - Black walnut & butternut

  30. Porosity of Hardwoods • Diffuse Porous Pours are evenly distributed in earlywood and latewood Most species have small diameter pores, (mahogany is the exception) Typical wood species – birch, maple, poplar, mahogany and basswood.

  31. Porosity of Hardwoods Another look

  32. Tyloses • As some wood species make the transition from sapwood to heartwood bubble like structures form, blocking the passage way between connected vessels • White Oak – used for wine barrels

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