Elm(Fig. 14) has an easily recognized feature of wavy bands of
pores dominating the latewood portion of the growth rings. These undu-
lating, more or less tangential bands are up to several pores wide and give
the latewood portion of growth rings a distinctive jagged appearance on
tangential board surfaces. A microscopic check of tangential sections will
show rays to be mostly 4–6 seriate.
Walnut(Fig. 15) is a typical semi-ring-porous wood. The larger
pores are usually visible without magnification, but pore size diminishes
across the growth ring, and the smallest latewood pores can be seen only
with a hand lens. Pores are solitary or in radial multiples of two to four.
Rays are distinct but not conspicuous when viewed on transverse surfaces
with a hand lens; on tangential surfaces examined microscopically, rays of
European walnut ( Juglans regia) are mostly 2–4 (occasionally 5) seriate. The
milk-chocolate color of the heartwood is also an important identification
characteristic.Diffuse-porous hardwoods
Woods in this group lack a distinct earlywood zone of larger pores when
examined in transverse surface with a hand lens. The term diffuse porous
implies that pores of more or less uniform size are distributed evenly
across the growth ring. Pores may be relatively large, as in many coarse-
textured tropical woods such as mahogany (Fig. 16); the largest pores of
coarse-textured hardwoods are visible without magnification, and the
large-diameter vessels exposed lengthwise along tangential or radial sur-
faces appear as distinct lines (called vessel lines). Diffuse-porous hard-
woods ofthe temperate regions, however, are typically fine textured; the
relatively small pores cannot be seen without magnification, and vessel
lines are indistinct to invisible. In a few woods, such as mahogany and
cherry, heartwood color may be useful. But most diffuse-porous woods are
nondistinctive pale shades oflight brown and, especially after centuries of
aging, some darken while others lighten. Ray size is helpful in identifying
some; pore size and arrangements are helpful in identifying others. A few
woods have characteristic patterns of parenchyma cells. With most diffuse-
porous woods, however, reliable identification requires the determination
ofmicroscopic features.
Vessel cells have several important microscopic features. The dis-
tinctive characteristic of vessel cells is that their end walls have openings
where they are joined end to end. These openings, called perforations,
enable the aligned vessel cells to form continuous conductive pipelines—
i.e., vessels. In most species the perforations are single large openings
called simple perforations;in other species, the vessel end walls have a series
of elongated openings separated by thin bars and forming ladderlike or
gratelike openings called scalariform perforations. Afew species have both
types ofperforations. They are best viewed in radial sections (Fig. 24a, b).
Another important microscopic feature is intervessel pitting (pits are small
voids in the cell walls). Where two vessels are in contact side by side (as
where a pore multiple is seen on a transverse surface), the common wall
joining the two vessels is relatively wide and has numerous pits. Because
pore multiples are more commonly radial, the shared tangential vessel
walls with intervessel pitting are most easily found by scanning tangential
sections. The appearance of these intervessel pits (size, shape, and
arrangement) may be an important identification characteristic for aI W P P 33a
b
Figure 24a, b
Radial sections showing examples of perfora-
tions, the openings in the end walls ofadjoin-
ing vessel cells in hardwoods: (a) scalariform
perforations in alder (Alnussp.); and (b) a
simple perforation in poplar (Populussp.).