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Lecture #5 - Anatomical Structure of Softwoods, part I

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

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Lecture #5 - Anatomical Structure of Softwoods, part I

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  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 WoodsLongitudinal 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 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.

  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”

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