All of our broadleaf woods are either ring-porous or diffuse-porous,
    though some of them, like the walnut, are nearly half way between
    the two groups.

If the wood of hickory, for example, be examined with the magnifying lens, it will be seen that there are numerous small pores in the late wood, while running parallel with the annual rings are little white lines such as are shown in Fig. 149.  These are lines of wood parenchyma.  Wood parenchyma is found in all woods, arranged sometimes in tangential lines, sometimes surrounding the pores and sometimes distributed over the cross-section.  The dark, horn-like portions of hickory and oak are the woodfibers.  They give the strength to wood.

In many of the diffuse-porous woods, the pores are too small to be seen with the unaided eye, and in some cases they are not very distinct even when viewed with a magnifier.  It is necessary to study such examples closely in order not to confuse them with the woods of conifers.

The woods of conifers are quite different in structure from broadleaf woods, though the difference may not always stand out prominently.  Coniferous woods have no pores, their rays are always narrow and inconspicuous, and wood parenchyma is never prominent.  The woods of the pines, spruces, larches, and Douglas fir differ from those of the other conifers in having resin ducts, Fig. 144.  In pines these are readily visible to the naked eye, appearing as resinous dots on cross-sections and as pin scratches or dark lines on longitudinal surfaces.  The presence or absence of resin ducts is a very important feature in identifying woods, hence it is very important to make a careful search for them when they are not readily visible.

How to identify a specimen of wood:  The first thing to do in identifying
    a piece of wood is to cut a smooth section at the end and note
    (without the magnifier) the color, the prominence of the rays and
    pores, and any other striking features.  If the pores are readily
    visible, the wood is from a broadleaf tree; if the large pores are
    collected in a ring it belongs to the ring-porous division of the
    broadleaf woods.  If the rays are quite conspicuous and the wood is
    hard and heavy, it is oak, as the key given later will show.  Close
    attention to the details of the key will enable one to decide to
    what group of oaks it belongs.

In most cases the structure will not stand out so prominently as in oak, so that it is necessary to make a careful study with the hand lens.  If pores appear, their arrangement, both in the early wood and in the late wood, should be carefully noted; also whether the pores are open or filled with a froth-like substance known as tyloses.  Wood parenchyma lines should be looked for, and if present, the arrangement of the lines should be noted.

[Illustration:  FIG. 148.—­(Magnified about 8 times.)]