2.2.1 Cell Types.
Tracheids. Tracheids are the principal longitudinal cell type in
softwoods. Tracheids, or fibers (Figure 2-6) as they are sometimes referred to, comprise 90 to 95
percent of the volume of the wood, and are about 100 times longer than they are in diameter. They
contribute greatly to the strength of a wood. The diameter of tracheids varies from one species to
the next. This difference is readily observed with a hand lens, and is useful for identification pur-
Parenchyma. Parenchyma cells are generally short, thin-walled cells
which are connected together in strands and serve primarily for storage and distribution of car-
Resin canals are tubular passageways lined with living parenchyma cells which exude resin or pitch.
In pine, resin canals are easily seen with the naked eye on the end grain as well as the side grain
220.127.116.11 Hardwoods. The hardwoods have more cell types and the variation in the
size and arrangement of these cells is greater than in the softwoods (Figure 2-8). As a result, the
hardwoods are more varied in appearance, and may have unique characteristics making certain
species more desirable for selected end uses than others.
Vessels (Pores). Vessels are relatively large diameter, thin-walled, round cells
that are connected end to end to form microscopic tubes that are ideal for sap conduction. It is the
vessels which constitute the pores in hardwoods (Figure 2-3). The presence of large diameter un-
obstructed vessels makes some woods easy to treat. Red oak is an example. Its structure is so open
that smoke can be blown through short pieces of the wood.
Fibers. Fibers are relatively small diameter, elongated cells with thick walls
and closed ends. Fibers are primarily responsible for the strength characteristics of hardwood.
Parenchyma. In the hardwoods, parenchyma cells vary widely in size and
arrangement. In oak, beech, and sycamore, the rays (mostly parenchyma cells) are conspicuous to
the naked eye and aid greatly in the identification of these species.
Miscellaneous. Hardwoods contain other miscellaneous features which are
often important in identification, as well as the end use of the product. For example, white oak con-
tains tyloses. Tyloses are literally plugs in the vessels or pores of this species group. Thus, white