Wood and Forest Part 45

KEY TO THE MORE IMPORTANT WOODS OF NORTH AMERICA.

I. NON-POROUS WOODS--Pores not visible or conspicuous on cross-section, even with magnifier. Annual rings distinct by denser (dark colored) bands of summer wood (Fig. 128).

[Ill.u.s.tration: Fig. 128. "Non-porous" Woods. _A_, fir; _B_, "hard"

pine; _C_, soft pine; _ar_, annual ring; _o.e._, outer edge of ring; _i.e._, inner edge of ring; _s.w._, summer wood; _sp.w._, spring wood; _rd._, resin ducts.]

II. RING-POROUS WOODS--Pores numerous, usually visible on cross-section without magnifier. Annual rings distinct by a zone of large pores collected in the spring wood, alternating with the denser summer wood (Fig. 129).

[Ill.u.s.tration: Fig. 129. "Ring-porous" Woods White Oak and Hickory.

_a. r._, annual ring; _su. w._, summer wood; _sp. w._, spring wood; _v_, vessels or pores; _c. l._, "concentric" lines; _rt_, darker tracts of hard fibers forming the firm part of oak wood; _pr_, pith rays.]

III. DIFFUSE-POROUS WOODS--Pores numerous, usually not plainly visible on cross-section without magnifier. Annual rings distinct by a fine line of denser summer wood cells, often quite indistinct; pores scattered thru annual ring, no zone of collected pores in spring wood (Fig. 130).

[Ill.u.s.tration: Fig. 130. "Diffuse-porous" Woods. _ar_, annual ring; _pr_, pith rays which are "broad" at _a_, "fine" at _b_, "indistinct"

at _d_.]

NOTE.--The above described three groups are exogenous, i.e., they grow by adding annually wood on their circ.u.mference. A fourth group is formed by the endogenous woods, like yuccas and palms, which do not grow by such additions.

I.--NON-POROUS WOODS.

(Includes all coniferous woods.)

A. Resin ducts wanting.[1]

1. No distinct heart-wood.

_a._ Color effect yellowish white; summer wood darker yellowish (under microscope pith ray without tracheids)..........FIRS.

_b._ Color effect reddish (roseate) (under microscope pith ray with tracheids) ................................HEMLOCK.

2. Heart-wood present, color decidedly different in kind from sap-wood.

_a._ Heart-wood light orange red; sap-wood, pale lemon; wood, heavy and hard .........................................YEW.

_b._ Heartwood purplish to brownish red; sap-wood yellowish white; wood soft to medium hard, light, usually with aromatic odor, ...................................RED CEDAR.

_c._ Heart-wood maroon to terra cotta or deep brownish red; sap-wood light orange to dark amber, very soft and light, no odor; pith rays very distinct, specially p.r.o.nounced on radial section ..................................REDWOOD.

3. Heart-wood present, color only different in shade from sap-wood, dingy-yellowish brown.

_a._ Odorless and tasteless ........................BALD CYPRESS.

_b._ Wood with mild resinous odor, but tasteless ....WHITE CEDAR.

_c._ Wood with strong resinous odor and peppery taste when freshly cut, ................................INCENSE CEDAR.

B. Resin ducts present.

1. No distinct heartwood; color white, resin ducts very small, not numerous ............................................SPRUCE.

2. Distinct heart-wood present.

_a._ Resin ducts numerous, evenly scattered thru the ring.

_a.'_ Transition from spring wood to summer wood gradual; annual ring distinguished by a fine line of dense summer-wood cells; color, white to yellowish red; wood soft and light .......................SOFT PINES.[2]

_b.'_ Transition from spring wood to summer wood more or less abrupt; broad bands of dark-colored summer wood; color from light to deep orange; wood medium hard and heavy ............................HARD PINES.[2]

_b._ Resin ducts not numerous nor evenly distributed.

_a'._ Color of heart-wood orange-reddish, sap-wood yellowish (same as hard pine); resin ducts frequently combined in groups of 8 to 30, forming lines on the cross-section (tracheids with spirals), ..............DOUGLAS SPRUCE.

_b'._ Color of heart-wood light russet brown; of sap-wood yellowish brown; resin ducts very few, irregularly scattered (tracheids without spirals) ........TAMARACK.

[Footnote 1: Soft and hard pines are arbitrary distinctions and the two not distinguishable at the limit.]

[Footnote 2: To discover the resin ducts a very smooth surface is necessary, since resin ducts are frequently seen only with difficulty, appearing on the cross-section as fine whiter or darker spots normally scattered singly, rarely in groups, usually in the summer wood of the annual ring. They are often much more easily seen on radial, and still more so on tangential sections, appearing there as fine lines or dots of open structure of different color or as indentations or pin scratches in a longitudinal direction.]

ADDITIONAL NOTES FOR DISTINCTIONS IN THE GROUP.

Spruce is hardly distinguishable from fir, except by the existence of the resin ducts, and microscopically by the presence of tracheids in the medullary rays. Spruce may also be confounded with soft pine, except for the heart-wood color of the latter and the larger, more frequent, and more readily visible resin ducts.

In the lumber yard, hemlock is usually recognized by color and the silvery character of its surface. Western hemlocks partake of this last character to a less degree.

Microscopically the white pine can be distinguished by having usually only one large pit, while spruce shows three to five very small pits in the parenchyma cells of the pith ray communicating with the tracheid.

The distinction of the pines is possible only by microscopic examination. The following distinctive features may a.s.sist in recognizing, when in the log or lumber pile, those usually found in the market:

The light, straw color, combined with great lightness and softness, distinguishes the white pines (white pine and sugar pine) from the hard pines (all others in the market), which may also be recognized by the gradual change of spring wood into summer wood. This change in hard pines is abrupt, making the summer wood appear as a sharply defined and more or less broad band.

The Norway pine, which may be confounded with the shortleaf pine, can be distinguished by being much lighter and softer. It may also, but more rarely, be confounded with heavier white pine, but for the sharper definition of the annual ring, weight, and hardness.

The longleaf pine is strikingly heavy, hard, and resinous, and usually very regular and narrow ringed, showing little sap-wood, and differing in this respect from the shortleaf pine and loblolly pine, which usually have wider rings and more sap-wood, the latter excelling in that respect.

The following convenient and useful cla.s.sification of pines into four groups, proposed by Dr. H. Mayr, is based on the appearance of the pith ray as seen in a radial section of the spring wood of any ring:

Section I. Walls of the tracheids of the pith ray with dentate projections.

_a._ One to two large, simple pits to each tracheid on the radial walls of the cells of the pith ray.--Group 1. Represented in this country only by _P. resinosa_.

_b._ Three to six simple pits to each tracheid, on the walls of the cells of the pith ray.--Group 2. _P. taeda_, _pal.u.s.tris_, etc., including most of our "hard" and "yellow" pines.

Section II. Walls of tracheids of pith ray smooth, without dentate projections.