Lecture #5 - Anatomical
Structure of Softwoods, part I
Forestry 280
Iowa State University
Cross-Section of Eastern White Pine
Cell Types of Coniferous Woods
Longitudinal Cells
 Tracheids –
Tracheids conduct
water/solutes and
provide mechanical
support.
 Two Types:
 Longitudinal
Tracheids
 Strand Tracheids
Radial Section (RS)
XS
Longitudinal Tracheids (LTs)
 Elongated cells with
thickened walls and
tapering, pointed ends
 Closed at the ends,
i.e., are “imperforate”
as opposed to the
vessel elements found
in hardwoods.
 Side walls of tracheids
contain pits.
Longitudinal Tracheids, continued
 Mature-wood softwood tracheids are
typically between 3-5 mm long and have a
l/d ratio of about 100; thus, the average
diameter of such cells would be 30-50
micrometers in (tangential) diameter.
 The radial diameter of LTs decreases from
earlywood to latewood.
 LTs typically comprise 90 to 94% of
softwood volume.
Strand Tracheids (STs)
 Strand tracheids are
short cells that are
arranged in
longitudinal strings
or “strands”
 STs have one or two
“square ends”
 They contain
bordered pits. They
are usually found
near a resin canal.
Parenchyma
 Parenchyma conduct and store food
and other substances.
 Longitudinal Parenchyma
 Epithelial Cells
Longitudinal Parenchyma





Relatively thin-walled
cells
Have simple pits
Form strands with
tapered ends
May contain darkly
staining substances
When present,
longitudinal
parenchyma are not
abundant.
Epithelial Cells




Epithelial cells form
the periphery of a
structure called a
resin canal (RC)
May be thin- or thickwalled
Collectively, they are
called “epithelium”
They excrete resin
into the RC
Epithelial Cells, continued
 “Normal” resin canals are found in four
domestic genera, namely Pinus (pines),
Picea (spruces), Larix (larches), and
Pseudotsuga (Douglas fir)
 “Traumatic” resin canals (i.e., those arising
in response to an injury to the tree) may be
found in these and other coniferous genera.
Longitudinal only.
Transverse Cells
 Ray Tracheids
 Ray Parenchyma
 Epithelial cells
Transverse Section of Sugar Pine
Ray Tracheids
 Have bordered pits
 Relatively thickwalled cells
 Interior walls are
either smooth or
dentate
 Not universally
present (i.e., not
found in all
genera).
Ray Parenchyma
 Universally present
in all genera
 Have simple pits
 Generally thinwalled, but some
may have relatively
thick, lignified walls
 End-walls may be
smooth, nodular or
indentured
Epithelial Cells
 These surround
transverse resin
canals
 May be thin- or
thick-walled
 Are part of a
composite
structure known
as a “fusiform ray”