Chapter XIII: Appendix: How to Distinguish the Different Kinds of Wood.a

BY B. E. FERNOW AND FILIBERT ROTH.

The carpenter or other artisan who handles different woods, becomes familiar with those he employs frequently, and learns to distinguish them thru this familiarity, without usually being able to state the points of distinction. If a wood comes before him with which he is not familiar, he has, of course, no means of determining what it is, and it is possible to select pieces even of those with which he is well acquainted, different in appearance from the general run, that will make him doubtful as to their identification. Furthermore, he may distinguish between hard and soft pines, between oak and ash, or between maple and birch, which are characteristically different; but when it comes to distinguishing between the several species of pine or oak or ash or birch, the absence of readily recognizable characters is such that but few practitioners can be relied upon to do it. Hence, in the market we find many species mixed and sold indiscriminately.

To identify the different woods it is necessary to have a knowledge of the definite, invariable differences in their structure, besides that of the often variable differences in their appearance. These structural differences may either be readily visible to the naked eye or with a magnifier, or they may require a microscopical examination. In some cases such an examination can not be dispensed with, if we would make absolutely sure. There are instances, as in the pines, where even our knowledge of the minute anatomical structure is not yet sufficient to make a sure identification.

In the following key an attempt has been made--the first, so far as we know, in English literature--to give a synoptical view of the distinctive features of the commoner woods of the United States, which are found in the markets or are used in the arts. It will be observed that the distinction has been carried in most instances no further than to genera or classes of woods, since the distinction of species can hardly be accomplished without elaborate microscopic study, and also that, as far as possible, reliance has been placed only on such characteristics as can be distinguished with the naked eye or a simple magnifying glass, in order to make the key useful to the largest number. Recourse has also been taken for the same reason to the less reliable and more variable general external appearance, color, taste, smell, weight, etc.

The user of the key must, however, realize that external appearance, such, for example, as color, is not only very variable but also very difficult to describe, individual observers differing especially in seeing and describing shades of color. The same is true of statements of size, when relative, and not accurately measured, while weight and hardness can perhaps be more readily approximated. Whether any feature is distinctly or only indistinctly seen will also depend somewhat on individual eyesight, opinion, or practice. In some cases the resemblance of different species is so close that only one other expedient will make distinction possible, namely, a knowledge of the region from which the wood has come. We know, for instance, that no longleaf pine grows in Arkansas and that no white pine can come from Alabama, and we can separate the white cedar, giant arbor vitae of the West and the arbor vitae of the Northeast, only by the difference of the locality from which the specimen comes. With all these limitations properly appreciated, the key will be found helpful toward greater familiarity with the woods which are more commonly met with.

The features which have been utilized in the key and with which--their names as well as their appearance--therefore, the reader must familiarize himself before attempting to use the key, are mostly described as they appear in cross-section. They are:

(1) Sap-wood and heart-wood (see p. 17), the former being the wood from the outer and the latter from the inner part of the tree. In some cases they differ only in shade, and in others in kind of color, the heart-wood exhibiting either a darker shade or a pronounced color. Since one can not always have the two together, or be certain whether he has sap-wood or heart-wood, reliance upon this feature is, to be sure, unsatisfactory, yet sometimes it is the only general characteristic that can be relied upon. If further assurance is desired, microscopic structure must be examined; in such cases reference has been made to the presence or absence of tracheids in pith rays and the structure of their walls, especially projections and spirals.

(2) Annual rings, their formation having been described on page 19. (See also Figs. 128-130.) They are more or less distinctly marked, and by such marking a classification of three great groups of wood is possible.

(3) Spring wood and summer wood, the former being the interior (first formed wood of the year), the latter the exterior (last formed) part of the ring. The proportion of each and the manner in which the one merges into the other are sometimes used, but more frequently the manner in which the pores appear distributed in either.

(4) Pores, which are vessels cut thru, appearing as holes in cross-section, in longitudinal section as channels, scratches, or identifications. (See p. 23 and Figs. 129 and 130.) They appear only in the broad-leaved, so called, hard woods; their relative size (large, medium, small, minute, and indistinct when they cease to be visible individually by the naked eye) and manner of distribution in the ring being of much importance, and especially in the summer wood, where they appear singly, in groups, or short broken lines, in continuous concentric, often wavy lines, or in radial branching lines.

(5) Resin ducts (see p. 26 and Fig. 128) which appear very much like pores in cross-section, namely, as holes or lighter or darker colored dots, but much more scattered. They occur only in coniferous woods, and their presence or absence, size, number, and distribution are an important distinction in these woods.

(6) Pith rays (see p. 21 and Figs. 129 and 130), which in cross-section appear as radial lines, and in radial section as interrupted bands of varying breadth, impart a peculiar luster to that section in some woods. They are most readily visible with the naked eye or with a magnifier in the broad-leaved woods. In coniferous woods they are usually so fine and closely packed that to the casual observer they do not appear. Their breadth and their greater or less distinctness are used as distinguishing marks, being styled fine, broad, distinct, very distinct, conspicuous, and indistinct when no longer visible by the naked (strong) eye.

(7) Concentric lines, appearing in the summer wood of certain species more or less distinct, resembling distantly the lines of pores but much finer and not consisting of pores. (See Fig. 129.)

Of microscopic features, the following only have been referred to:

(8) Tracheids, a description of which is to be found on page 28.

(9) Pits, simple and bordered, especially the number of simple pits in the cells of the pith rays, which lead into each of the adjoining tracheids.

For standards of weight, consult table on pages 50 and 192; for standards of hardness, table on page 195.

Unless otherwise stated the color refers always to the fresh cross-section of a piece of dry wood; sometimes distinct kinds of color, sometimes only shades, and often only general color effects appear.

[Footnote A: From Forestry Bulletin No. 10, _U. S. Department
of Agriculture_.]

HOW TO USE THE KEY.

Nobody need expect to be able to use successfully any key for the distinction of woods or of any other class of natural objects without some practice. This is especially true with regard to woods, which are apt to vary much, and when the key is based on such meager general data as the present. The best course to adopt is to supply one's self with a small sample collection of woods, accurately named. Small, polished tablets are of little use for this purpose. The pieces should be large enough, if possible, to include pith and bark, and of sufficient width to permit ready inspection of the cross-section. By examining these with the aid of the key, beginning with the better-known woods, one will soon learn to see the features described and to form an idea of the relative standards which the maker of the key had in mind. To aid in this, the accompanying illustrations will be of advantage. When the reader becomes familiar with the key, the work of identifying any given piece will be comparatively easy. The material to be examined must, of course, be suitably prepared. It should be moistened; all cuts should be made with a very sharp knife or razor and be clean and smooth, for a bruised surface reveals but little structure. The most useful cut may be made along one of the edges. Instructive, thin, small sections may be made with a sharp penknife or razor, and when placed on a piece of thin glass, moistened and covered with another piece of glass, they may be examined by holding them toward the light.

Finding, on examination with the magnifier, that it contains pores, we know it is not coniferous or non-porous. Finding no pores collected in the spring-wood portion of the annual ring, but all scattered (diffused) thru the ring, we turn at once to the class of "Diffuse-porous woods." We now note the size and manner in which the pores are distributed thru the ring. Finding them very small and neither conspicuously grouped, nor larger nor more abundant in the spring-wood, we turn to the third group of this class. We now note the pith rays, and finding them neither broad nor conspicuous, but difficult to distinguish, even with the magnifier, we at once exclude the wood from the first two sections of this group and place it in the third, which is represented by only one kind, cottonwood. Finding the wood very soft, white, and on the longitudinal section with a silky luster, we are further assured that our determination is correct. We may now turn to the list of woods and obtain further information regarding the occurrence, qualities, and uses of the wood.

Sometimes our progress is not so easy; we may waver in what group or section to place the wood before us. In such cases we may try each of the doubtful roads until we reach a point where we find ourselves entirely wrong and then return and take up another line; or we may anticipate some of the later mentioned features and finding them apply to our specimen, gain additional assurance of the direction we ought to travel. Color will often help us to arrive at a speedy decision. In many cases, especially with conifers, which are rather difficult to distinguish, a knowledge of the locality from which the specimen comes is at once decisive. Thus, northern white cedar, and bald cypress, and the cedar of the Pacific will be identified, even without the somewhat indefinite criteria given in the key.

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).

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).

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).

NOTE.--The above described three groups are exogenous, i.e., they grow by adding annually wood on their circumference. 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 pronounced
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.]

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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 assist 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 classification 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: