Forest Utilisation Chapter 8: Anatomical Structure of Wood, Sapwood, Heartwood, Vessels and Rays

Forest Utilisation Notes · Chapter 8

Chapter 8: Anatomical Structure of Wood

Cell development and pits, pith, sapwood and heartwood, bark, early and late wood, growth rings, vessels, ring and diffuse porous woods, tyloses, tracheids, fibres, parenchyma, rays, ripple marks and resin canals.

CellGross structureMinute structureTree formRevisionMCQ quiz

1. The cell

A group of similar cells doing the same work is a tissue. Height growth takes place at the tips and girth growth in the cambium.

Cell division

↓

Cell enlargement and wall thickening

↓

Lignification (cell hardening)

PitsDuring the course of secondary thickening certain places in the primary cell wall are left uncovered, and these thin places in the wall which serve as a means of inter-communication between two adjacent cells are known as pits.

Liquids move through the tree mainly through pits. Once lignified, a cell cannot enlarge further.

2. Gross structure (seen with naked eye or pocket lens)

Pith

Small soft mass of tissue in the centre; no special function and no diagnostic value.

Sapwood

Light coloured outer part with the youngest rings; food storage and sap conduction. Liable to fungal attack because of stored starch.

Heartwood

Deep coloured central dead tissue giving mechanical support; more durable because of gums, resins and oils that are toxic to fungi and insects.

Bark

Outer corky dead zone and inner living zone that conducts and stores food; useful in identification.

Sapwood and heartwoodThe light coloured outer portion of a tree log consisting of the youngest growth rings is called sapwood and the deep coloured central portion heartwood.

Growth ringsThese are concentric rings which usually represent the wood formed during one growing season; also called, though less aptly, annual rings.

'All sapwood' trees show no colour difference between sapwood and heartwood: fir, spruce, mango, haldu, semal, bahera, Ficus, bel and kadam. Colour can mislead: in ebony the black wood is not true heartwood, and sal sapwood can be reddish.

Early (spring) wood is formed fast with thin-walled cells and more pores; late (summer or autumn) wood is slower, thick-walled and darker. Rings are 5 to 25 mm wide in fast-grown timber and 8 or more per cm in slow-grown timber.

3. Minute structure

Element	Description
Vessels (pores)	Short wide cells forming tubes that conduct sap in broad-leaved trees. Absent in conifers except near the pith.
Tracheids	In softwoods, one cell type does both conduction and support: hollow, needle-shaped, with large bordered pits; cross-section like a honeycomb.
Fibres	Narrow spindle-shaped cells with pointed closed ends; give strength in broad-leaved woods.
Parenchyma	Short thin-walled cells for storage and conduction of food; vertical parenchyma usually absent in conifers.
Wood (medullary) rays	Horizontal cells running radially; radial conduction and food storage. Give silver grain on quarter-sawn faces.
Tyloses	Ingrowths into vessels, foam-like, mostly in heartwood. Increase durability but make impregnation difficult.
Pith flecks	Patches of parenchyma caused by insects in the cambium
Ripple marks	Rays in tiers (storeys) giving fine wavy lines on the tangential face; useful for identification
Resin canals and gum ducts	Intercellular cavities. Pine and spruce have vertical and horizontal canals; sal and toon have gum ducts in bands; gurjan, chir and spruce have them evenly spread.

Ring-porous wood

Early-wood vessels clearly larger than late-wood vessels, forming a band. Rare in India: teak and toon.

Diffuse-porous wood

Vessels of similar size scattered through the ring. The majority of Indian hardwoods, owing to a long growing season.

Memory trick: Teak and Toon are Two ring-porous Timbers. Most Indian hardwoods are diffuse-porous.

Exam point: On the transverse section rays appear as radial lines, on the tangential section as short vertical lines, and on the radial section as horizontal ribbons.

4. Shape and size of trees

• Species: fir and pine give tall straight stems; mango and oaks branch in the open.
• Density of crop: dense crops give long clean boles and small crowns.
• Age: near maturity branchwood is only 8 to 10% of the stem wood.
• Soil and locality: better sites give more stem wood.
• Silvicultural system: even-aged woods give clean boles; selection gives shorter, more tapering boles; coppice gives fuel and small timber.

5. Quick revision

• Cell stages: division, enlargement and thickening, lignification. Pits link adjacent cells.
• Heartwood is more durable because of toxic gums, resins and oils.
• All-sapwood trees: fir, spruce, mango, haldu, semal, kadam.
• Vessels are absent in conifers; tracheids do conduction and support.
• Ring-porous: teak, toon (rare in India). Most Indian hardwoods are diffuse-porous.
• Tyloses: improve durability, hinder impregnation.
• Rays give silver grain; storeyed rays give ripple marks.

6. Interactive MCQ Quiz

15 questions. Tap an option to see the answer and explanation, then go to the next question.

Forest Utilisation NotesAll Forest Utilisation notes →

← PreviousChapter 7: Grading rules, defects and teak log classesNext →Chapter 9: Weight, strength, fuel value and defects

Ch 1Ch 2Ch 3Ch 4Ch 5Ch 6Ch 7Ch 8Ch 9Ch 10Ch 11Ch 12Ch 13Ch 14Ch 15Ch 16Ch 17Ch 18Ch 19