A. Coniferous Trees (Needle-Leaved, Naked-Seeded, Such As Pines, Cedars, Etc.), Soft Woods

1. Bark - outside or protecting tissue, thickest and roughest near the base, forms about 10 per cent of the entire trunk in space.

2. Pith or medulla - thickness varying from 1/5 of an inch in Norway pine to 1/25 of an inch in cypress.

3. Sap wood - the living portion of the tree - composed of many-sided, thin-walled cells - the zone next to the bark containing about 50 annual rings - wood light in color - cells very active and very numerous - assist in the life processes of the tree. In old trees about 40 per cent sapwood, in young trees nearly all of the trunk sapwood.

4. Heart wood - the inner zone - fibrous bundles - the darker part of the log - cells lifeless - gives strength to the tree.

5. Annual rings - concentric rings one of which is added yearly - seen on the cross section of a log. By counting these rings the approximate age of a tree may be determined.

1 For "Key to the More Important Woods of North America," see Appendix A, page 233.

6. Spring and summer. wood - the inner, softer, lighter-colored part of the annual ring caused by rapid growth called spring wood - the outer, or peripheral, firmer and darker-colored portion of the annual ring, caused by slower growth, called summer wood.

7. Anatomical structure - very porous - little tubes arranged in straight radial rows, resin ducts found in summer wood - cells long with pointed ends - dark lines, called medullary rays, run radially from the center toward the bark - structure simple and regular - growth stops during the winter.

B. The Dicotyledonous, Or Deciduous Trees (With Two Seed Leaves, Broad-Leaved Trees, Such As Oak, Maple, Beech, Etc.)

1. Bark, pith, sapwood and heartwood arranged the same as in coniferous trees, having the same function.

2. Color - varies in different trees.

3. Wood - translucent - exposure to air and sunlight changes color - kinds of wood sometimes distinguished by odor, such as cedar, pine, oak, etc.

C. The monocotyledonous trees (with one seed leaf, such as palms, yuccas, etc.). 1. Structure - bundles of tissue arise, placed irregularly in the soft tissue or pith, extend from the apex of the leaf to the small ends of the roots - each new leaf has its own bundles of tissue in the stem.

II. Composition Of Wood

A. Cells of sapwood - composed of cellulose, albuminoids, starchy matter, oils and water holding in solution sugars, gums, and acids.

B. Cells of heartwood - walls thick and contain a dense substance called lignin which gives elasticity and hardness to wood.

C. Elements found in wood - carbon, hydrogen, oxygen, nitrogen, sulphur, potassium, iron, phosphorus, calcium, sodium, silicon, and sometimes traces of other elements.

III. Decay Of Trees

A. How detected - top branches refuse to send forth leaves - dead and broken branches - decay of bark.

B. Causes - diseases of tree, parasitic insects, fungi, injury, etc.

IV. Lumbering

A. Season for cutting trees - late fall and winter, because the growing and conducting cells are less active.

B. How cut - with axes and saws - limbs trimmed - trunk of tree cut to desired lengths for logs - logs transported to saw mills and sawed into lumber - lumber piled up to season - lumber transported to dealers or to manufacturers.