WPS 224 Hardwood structure

Hardwood features

• 4 major types of cells which each make up about 15+% of total volume.

• Vessels are unique to hardwoods.

• Wide rays in some species. 17% volume average.

• Rays seldom aligned in straight radial rows.

• Usually less dense than softwoods.

Longitudinal cells

• Produced by fusiform initial division in cambium.

• Visual differences & lack in radial alignment only prominent in cell maturation.

Vessels

• Made up of vessel elements. Much larger diameter and shorter length than most longitudinal cells. Shorter than HW fibre & SW tracheid.

• Vessel elements link end to end to form tube-like structures called vessels, which have considerable tangential variation (not straight). This ensures that each branch of the crown receives water from many different roots. Safety feature against root damage.

• Diameter size and arrangement used in identification.

• Side-to-side connection by bordered pits. Can be connected to fiber tracheids, longitudinal and ray parenchyma via pits.

Vessel perforation plates

• Are vessel element end walls (end-to-end connections). Holes in plates are called perforations.

• Formed at end of cell maturation when enzymes such as cellulase dissolve portions of perforation plates.

• Perforation shape used in identification.

Tyloses

• Outgrowths of parenchyma cells into the hollow lumens of vessels.

• Commonly form in many hardwoods as a result of wounding and effectively act to prevent water loss from the area around damaged tissue.

• Block vessels.

Fibres

• More specifically called fiber tracheids.

• Long, tapered, and usually thick‐walled cells. Much shorter and rounder than SW tracheids.

• Primary function is mechanical support.

• Bordered pits between fibre tracheids, but half bordered between fibre tracheids and parenchyma.

• Libriform fibre has simple pits instead.

Longitudinal parenchyma

• Thin walled storage units.

• Occur in the form of long, tapered longitudinal cells, short, brick‐shaped epithelium around gum canals (in only a few species), and ray cells.

• Can be 24% of total volume.

• Unlike in SW, occurs in many HW.

Parenchyma arrangements (transverse view)

Rays

• Tangential width of 1-30 cells.

• Homogeneous of parenchyma cell type.

• Square ray cells are sqaure when viewed radially.

  • Procumbent ray cells are when the cells’ long dimension is perpendicular to the axes of longitudinal cells.

  • Upright ray cells are when the cells stand on end with their long axes parallel to the grain direction.

• Storied ray cells are arranged into definite tiers as viewed on a tangential surface. Rays in each layer are roughly the same height, and all begin and end at about the same level along the grain.

Identification