WPS 224 Softwood structure

Longitudinal tracheids

• 90-95% of total tree volume.

• Hollow centre (lumen), closed ends, pits are normally bordered.

• ~100 times longer than wide.

Pitting

• Pits on longitudinal tracheids. Bordered.

• They typify tracheid-to-tracheid linkages, therefore pit location matches adjacent tracheids.

Aspired pits

• Pit whose membrane is flexible, making it shift to one side, blocking the aperture by the impenetrable torus.

• Drying can be a cause because of liquid pressure differences.

• Occurs more frequently in earlywood.

• Wood with apsired pits are resistant to the penetration of chemicals and preservatives, and dry slowly.

Longitudinal parenchyma

• Rare amongst species.

• Same general shape of tracheids. Occurs as longitudinal strands of short cells butted end-to-end.

• 1-2% of total tree volume.

Epithelium

• Horizontal and longitudinal resin canals always accompany each other.

• Horizontal canals found in some rays.

• Intercellular space surrounded by specialized parenchyma cells that secrete resin into the canal. Can be created via trauma.

• Aids in healing, repels insects & other outsiders.

Rays

• Uniformly narrow rays characterize softwoods, except where horizontal resin canals are present.

• In tangential view rays are usually one to a few cells wide. Uniseriate and biseriate.

• Composed of either ray parenchyma (thick or thin walled, pits or no pits) or ray tracheids (thick walled, bordered pits), or both. Homogeneous or heterogeneous rays.

Dentate ray tracheids

• Ray tracheids that form secondary walls that are locally thickened in the vicinity of pits. Look like teeth.

Fusiform ray

• Ray that contains resin canal.

Crossfield pitting

• Crossfield pitting occurs at the intersections of longitudinal tracheids and ray parenchyma, and the half‐bordered pits are of unique form.

• Occurs in all softwoods.

• Useful in identification of species, because of variation of shapes in radial view.

Identification