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 averaging not less than four annual rings per inch one-half summerwood are also classified as
dense. Fast growth southern pine may have only two or three growth increments per inch and a rela-
tively small percentage of latewood. Due to its lower strength properties, this material is placed in a
lower grade. The specifications for railroad crossties also recognize the importance of growth rate
in the softwoods. These specifications indicate that the purchaser may specify that any inch of any
radius from the pith shall have six or more rings of annual growth throughout the top fourth of the
tie.
The latewood in softwoods is more easily treated with wood preservatives than earlywood.
2.1.2.3 "Pores". The distribution of large diameter cells (pores) within growth in-
crements of hardwoods allows grouping of these hardwoods into three categories based on their
cross sectional appearance (Figure 2-3). These categories are: ring porous, semi-ring porous, and
diffuse porous. Ring porous woods have large diameter pores at the beginning of each growth incre-
ment. The pores can be easily seen with the naked eye. Ring porous woods include oak, ash and
elm. Semi-ring porous woods, on the other hand, have pores that are initially large and then gradual-
ly decrease in diameter throughout the growth increment. Examples of semi-ring porous woods in-
clude walnut and butternut. In diffuse porous woods, the pores are uniform in size across the entire
growth increment and are generally too small to be seen without the use of a hand lens. Diffuse
porous woods include maples, yellow poplar, sweetgum, and others.
2.1.3 Grain (Planes Or Surfaces). Visible characteristics, shrinkage and mechanical
properties of wood are defined in terms of the three planes in which wood can be cut (Figure 2-l).
Characteristics of these surfaces can also be useful in the identification of wood. In reality, how-
ever, very few boards are perfectly cut on one of these planes. The saw cut usually ends up at some
angle between them.
2.1.3.1 End. End gram (cross section) is the surface exposed when wood is cut
across the width of a log or board. The end gram reveals the annual rings and, thus, is a key surface
for identification of wood when using a hand lens to determine cell structure.
Because the end gram is porous it absorbs preservatives more easily than side gram (radial or tan-
gential)
2.1.3.2 Radial. The radial surface is exposed when a log is cut longitudinally
from its center to the bark (along the radius). In the hardwood industry, lumber cut this way is
known as quartered lumber. Some large timbers and railroad ties will show ray flecks if on one face
a large log is cut through the pith (Figure 2-4). Sycamore and beech are two more wood species
which can be quartered to show distinctive ray flecks, but these are not as large as in oak. Some
softwood species, such as southern pine and Douglas-fir, are quartered to expose a vertical gram pat-
tern, and are used for flooring because of the high resistance to wear. This lumber is sometimes
referred to as edge grain (Figure 2-2).
2-5
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