Plants & Human Affairs (BIOL106)  -  Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; ssaupe@csbsju.edu; http://www.employees.csbsju.edu/ssaupe

Wood Exercises & Study Questions

Objectives:  At the conclusion of this exercise/unit you should be able to:

1. distinguish between trees, shrubs, herbs and vines
2. identify and give the function of the major cell types in the xylem
3. describe the function and location of xylem and phloem in a woody plant
4. define meristem and give examples
5. identify the major features visible in the cross section of a tree, including rays, annual rings, grain, latewood (summerwood), early wood (spring wood)
6. distinguish between ring-porous and diffuse-porous wood
7. distinguish between a hardwood and softwood
8. recognize the wood of common species in central Minnesota
9. describe the difference between radial, tangential and transverse sections
10. describe the difference between quarter sawn and plain sawn boards.
11. determine the age of a tree from its wood
12. explain why trees have growth rings
13. list important wood products

Annual Rings:
     Each year a new layer of wood is produced by a tree. By counting the number or layers, or annual growth rings, the age of the tree can be determined. The width of the ring provides an indication of the growing conditions in that year. Study a wood block or sketch.

• Can you tell from looking at the rings which direction is toward the middle of the stem?
• Vessels produced early in the season are ____________ (larger or smaller) than those produced later in the growing season.
• Which is darker colored, early (spring) or late (summer) wood?
• If given woody stem, can you tell how old it is?
• If given a section of tree cut in 1991, can you determine what were the three best and three worst years for growth?

Wood Cuts: 
     The three standard cuts of wood are transverse (cross sectional), radial and tangential.  Can you draw a section of wood and then:

• Indicate a transverse (or cross sectional) cut

• Indicate a radial cut

• Indicate a tangential cut

• If provided with a piece of wood, can you determine which way it has been cut - transverse, radial or tangential?

• Explain how the cut affects the appearance of the board.

Quarter Sawn vs. Plain Sawn Boards: 
     By examining the figure (= appearance) of a board, it is possible to tell if it was plain‑sawed or quarter‑sawed.

• A tangential cut results in a ___________ ‑sawed board.

• A radial cut results in a ____________ ‑sawed board.

• The annual rings will run roughly parallel in a __________‑sawed board, but will appear triangular in a ______________‑sawed board.

• Draw a sketch of the appearance of a plain‑sawed board.

• Draw a sketch of the appearance of a quarter-sawn board.

Heartwood and Sapwood:
    If given a transverse section of a tree, can you distinguish the heartwood and sapwood.  Sketch a pie shaped section of this specimen and label heartwood, sapwood, bark, annual ring, ray, vascular cambium.

• Which wood is older, heart‑ or sapwood?  Explain.

• Which wood is generally darker colored, heart‑ or sapwood? Explain.

Cell Types of Wood: 
    The two major water conducting cells in wood are tracheids and vessels. 

• The diameter of a tracheid is ____________ (larger or smaller) than a vessel

• Identify the primary water conducting cell in the following woods:

Wood Porosity: 
    The vessels in wood are also termed the pores.  The distribution of vessels in wood is species-specific and can be useful for identifying wood.  Ring-porous refers to wood in which the vessels are arranged parallel to the ring.  In diffuse-porous wood, the vessels are scattered throughout the ring. Using the wood samples provided, do you observe any vessels or pores in the wood of spruce, oak or pine?

Wood Forensics:
    Wood played a major role in solving the murder of Charles Lindbergh's infant son.  Describe this case and the type of information derived from wood that was used to solve it.

Tyloses:
    Vessel cells can become plugged by outgrowths from the parenchyma cells called tyloses.  These bubble-like structures can accumulate a variety of resins and other materials that effectively plugs up the vessel.  Tyloses are usually formed when sapwood changes into heartwood, but can be formed at any time (Sharp, 1990).  Tyloses are common in white oak and black locust and a characteristics of wood used in tight cooperage (barrel making). 

    Obtain a twig (1/4 to 1/2 inch diameter) from red oak and white oak.  Attach a rubber hose to one end of the twig and attach the other end to a water outlet.  Slowly turn on the water and observe the end of the twig.  On which twig, in either, do drops of water appear?  Explain why.  Which wood would make better barrels? 

Some Study Questions:

1. If given a log, can you show where to make the following cuts: transverse (cross section), radial, and tangential?
2. Can you identify on a piece of wood, whether it has been cut transversely, radially or tangentially?
3. If you drive a nail into a tree, list the sequence of cells/tissues that you would encounter from outside to inside.
4. Compare and contrast veneer & plywood.
5. What are the dimensions of a 2 x 4?  Explain.
6. Can you define/use the following terms:

References:

• Sharp, JB 1990  Wood Identification.  A Manual for the Non-Professional.  University of Tennessee Agricultural Extension Service.  Publication 1389.
• Palenik, S (1983) Microscopic trace evidence - the overlooked clue.  The Microscope 31: 1 - 14.

 

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Last updated:  11/19/2008 / � Copyright  by SG Saupe /