1. Lecture #5 - Anatomical Structure of Softwoods, part I
Forestry 280
Iowa State University

2. Cross-Section of Eastern White Pine

3. Cell Types of Coniferous Woods Longitudinal Cells
Tracheids – Tracheids conduct water/solutes and provide mechanical support.
Two Types:
Longitudinal Tracheids
Strand Tracheids XS
Radial Section (RS)

4. 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.

5. 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 micrometers in (tangential) diameter.
The radial diameter of LTs decreases from earlywood to latewood.
LTs typically comprise 90 to 94% of softwood volume.

6. 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.

7. Parenchyma Parenchyma conduct and store food and other substances.
Longitudinal Parenchyma
Epithelial Cells

8. 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.

9. Epithelial Cells
Epithelial cells form the periphery of a structure called a resin canal (RC)
May be thin- or thick-walled
Collectively, they are called “epithelium”
They excrete resin into the RC

10. 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.

11. Transverse Cells
Ray Tracheids
Ray Parenchyma
Epithelial cells

12. Transverse Section of Sugar Pine

13. Ray Tracheids Have bordered pits Relatively thick-walled cells
Interior walls are either smooth or dentate
Not universally present (i.e., not found in all genera).

14. Ray Parenchyma Universally present in all genera Have simple pits
Generally thin-walled, but some may have relatively thick, lignified walls
End-walls may be smooth, nodular or indentured

15. Epithelial Cells These surround transverse resin canals
May be thin- or thick-walled
Are part of a composite structure known as a “fusiform ray”