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 • Most cells are elongated • The cell axis is oriented vertically
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)
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
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
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.
Photosynthesis • Sap (sugar) is carried downward through the inner bark, distributed to the cambium layer where new cells are built.
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?
More AboutCell Reproduction • Division of cambium cells takes place lengthwise. • Sister cells are created
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
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
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
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
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
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
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
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
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
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
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.
Porosity of Hardwoods Another look
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