matching pits in adjacent cells), the smoothness of the cell walls, and the
presence and color of the cell contents. Conifers that contain vertical resin
canals, evident on transverse surfaces, also contain horizontal resin canals
located within special rays called fusiformrays (Fig. 8). Therefore, the pres-
ence of resin canals can be confirmed by locating fusiform rays on tangen-
tial sections examined microscopically. Scots pine and fir are separated
from one another and from spruce and larch by microscopic examination
of radial sections (Figs. 9a–c). On such sections, groups of smaller (hori-
zontal) ray cells will be evident crossing perpendicular to the larger (verti-
cal) longitudinal tracheids. Of special significance are the cross fields—the
rectangular areas formed where individual ray cells contact individual lon-
gitudinal tracheids. The pits occurring on these cross fields are classified
in terms ofsize and shape. Scots pine, the principal pine of Europe and
Asia, is distinct in having dentate ray tracheids (tracheids with jagged or
toothed walls) and large cross-field pits (called windowlike pits) in the ray
parenchyma cells (Fig. 9a). European larch (Larix decidua) and Norway
spruce (Picea abies) have more or less smooth-walled ray tracheids and
small multiple cross-field pits (called piceoid pits, each typically a rounded
pit with a diagonal slash, similar in appearance to the Greek letter phi)
in the ray parenchyma cells (Fig. 9b). Larch and spruce are separated by
examination (in radial sections) of the first-formed longitudinal tracheids28 Hoadley
Figure 4, right
Pine (Pinus sylvestris), transverse surface.
Figure 5, far right
Spruce (Piceasp.), transverse surface.
Figure 6, right
Larch (Larixsp.), transverse surface.
Figure 7, far right
Fir (Abiessp.), transverse surface.
Figure 8
Tangential section of spruce (Picea sp.) show-
ing several uniseriate rays and one fusiform
ra y with a centrally located transverse
resin canal.