Wood Structure

• Storage/transport of nutrients

• Stability and Strength

• cambial growth

• Formation of rings only in climate zones with a distinct annual rythm

• Earlywood: low density, water transport

• Latewood: high density, mechanical stability

• In tropical regions: no growth rings

• Hardwoods evolutionary younger

• HW: higher level of specialization in structure

• Earlywood tracheids: thin cell walls, wide lumina —> water transport

• Latewood tracheids: thick cell walls, narrow lumina —> mechanical functions

• Structural parameters of one cell type are varied according to the function

• Tracheids: dead after differentiation

• Parenchyma cells in wood rays are living

• Mainly in wood rays

• storage function

• resin production (Epithelzellen)

• Production of extractives

• Living cells until heartwood formation

• Connections between cells

• Membrane: thickend to torus in the middle

• Hoftüpfel: Randwulst umgibt Torus mit Porus; rundlich bei Früholz

• Vewrschliessen sich, um den Baum zu schützen z.B. bei Verletzungen oder zu hohem Wasservorkommen

• Tüpfelpaar: sich ergänzende Tüpfel angrenzender Zellen

• Vessels: thin cell walls, wide lumina —> water transport

• Fibres/Fibertracheids: thick cell walls, narrow lumina —> mechanical function

• Specific cell types for each function

Large pit fields between vessels

• Middle lamella, primary and secondary cell wall

• Parallel texture of cellulose in secondary walls

• Can be distinguished on the bassis of orientation of cellulose fibrils (MFA)

• 40% Cellulose

• 31% Hemicellulose

• 29% Lignin

• More Ligning in softwoods

Polymerization of Glucose units

• 2 Glucose —> Cellobiose-unit

• Degree of polymerization: 7000-15000

• For strength

• Various sugar units

• Side chains

• For flexibility

• Phenolic subuntits

• For stiffness

• Heartwood: Inner dead part —> no transport, no living cells

• Sapwood: Outer, functional part —> water transport, parenchyma cells

• Tylosis clog vessels in hardwoods

Juvenile wood: higher MFA, lower density 

• compression wood: softwoods —> higher MFA

• tension wood: hardwoods —> lower MFA