Wood Diversity

1. Wood diversity

2. What is Wood
• Wood is a porous and fibrous structural tissue found in the stems and roots of trees and
other woody plants.
• It is an organic material – a natural composite of cellulose fibers that having capacity to face
different kind of tension and embedded in a matrix of lignin that resists compression.
• Wood is sometimes defined as only the secondary xylem in the stems of trees, or it is
defined more broadly to include the same type of tissue elsewhere such as in the roots of
trees or shrubs.
• In a living tree it performs a support function, enabling woody plants to grow large or to
stand up by themselves.
• It also conveys water and nutrients between the leaves, other growing tissues, and the roots.

3. • Classification of wood
(A) on the basis of amount of parenchyma wood is classified into two groups:
1. Manoxylic wood: such type of wood contains more living parenchyma.
⮚ It is soft and loose wood e.g., Cycas.
⮚ In these secondary vascular tissues with large amounts of softer storage cells (i.e.,
Parenchyma) mixed with the wood or xylem cells (i.e., Tracheids).
⮚The stems of these plants are softer than the wood of trees we use for lumber.
⮚Examples of plants with manoxylic wood are sago palms or cycads, the spurs or short
shoots of ginkgo trees, as well as many extinct seed fern groups.

5. 2. Pycnoxylic wood:
⮚such wood contains less amount of living parenchyma.
⮚It is hard wood. Such types of wood are found in most of the plants and in
these secondary vascular tissues with copious amount of xylem cells (e.g.
Tracheids) and little parenchyma.
⮚This wood is much stronger and durable.
⮚ Examples of plants with pycnoxylic wood are conifers or cone-bearing trees,
the long shoots of ginkgo, and most of angiosperms

6. (B) on the basis of distribution of parenchyma wood is classified into three groups:
1. Apotracheal: in this type of wood parenchyma is in scattered form and not in the contact of vessels e.g.,
Gymnosperms
2. Paratracheal wood: in this wood parenchyma is arranged or distributed in the form of masses or group.
In this type parenchyma is in contacts of pore like tissue i.e vessels e.g., Dicot plants.

7. Apotracheal parenchyma maybe divided into following types:
• (1)Diffuse or scattered- When the apotracheal parenchyma occurs as isolated cells or short tangential aggregates, the
distribution is described as diffuse or scattered. e.g., Adina cordifolia, Dillenia
• (2) Diffuse-in-aggregates- Here, the apotracheal parenchyma occurs in the form of fine and evenly spaced broken or
tangential lines. This type of distribution is also referred to as fine line distribution. e.g., Dipterocarpus, Hopea
parviflora
• (3) Banded- In this type the parenchyma forms relatively conspicuous tangential bands, occurring at frequent intervals
throughout the growth rings. When the band is broad and conspicuous, it is termed as banded-broad (e.g., Pterygota)
and when fine and narrow, it is called banded-narrow. (e.g., Lophopetalum)
The Paratracheal parenchyma shows following variations:
• 1.Vasicentric - When parenchyma is closely associated with the pores, forming a fairly uniform light coloured sheath
around the vessels, it is known as vasicentric. (e.g., Acacia catechu)
• 2. Aliform - In this type of parenchyma surrounds the vessels in such a way that wing like lateral projections are
formed. It is also known as eyelet type. (e.g., Albizzia lebbek , Holoptelea integrifolia).
• 3. Aliform confluent - It is a modification of aliform type. Here the wing like extensions of adjacent pores becomes
connected laterally. Such distribution may either be found independently or in association with aliform type. (e.g.,
Ongelnia cojeinensis). When adjacent connecting pores are thin and narrow, it is called confluent narrow and when
relatively broa then confluent broad.

9. C) Classification based on vessels:
On the 'basis of presence or absence of vessels, wood is classified in two categories
1. Non-porous soft wood: vessels are absent in such type of wood e.g. Gymnosperms
2. Porous wood: vessels are present in such type of wood. On the basis of arrangement of vessels porous wood is divided into
two groups.
(A) ring porous wood: vessels are arranged in the form of a ring in this type of wood. Such wood conducts water more
efficiently e.g., In temperate region as in dalbergia
(B) diffused porous wood: asystematical distribution of vessels is found in this type of wood in tropical region as in
azadirachta

12. Types of wood on the basis of Formation of Annual rings
• Annual rings are formed due to unequal activity of vascular cambium.
• The activity of cambium does not remain same; it is changeable in the whole
year. Activity of vascular cambium is affected by physiological and
environmental factors.
• In winter or autumn season the activity of the cambium is less and the
secondary xylem or wood formed is not extensive through the vascular
cambium.
• Cells formed during this period are small thick walled and have narrow
lumens. This is called autumn wood or late wood.
• The vascular cambium is highly active in spring or summer season and
secondary xylem formed during this period is extensive and cells of
secondary xylem are larger, thin walled and have wider lumen.
• This wood is known as spring wood or early wood. The spring wood is
lighter in colour and exhibits low density whereas the autumn (or winter)
wood is darker and has higher density

13. • The autumn and spring wood is formed in the form of rings.
• The ring of any type of wood is called growth ring. Thus, two growth rings are
formed in one year.
• A ring of autumn wood and a ring of spring wood are collectively/known as
annual ring. Thus, are annual ring consisting of two growth rings. The number of
annual rings, formed in a tree gives the idea of the age of the tree.
• The study of determination of age of the plant by these techniques is called
Dendrochronology.
• The annual rings are counted from the base of the stem because basal part has
maximum annual rings and upper part has less. Therefore, counting from the basal
region can give the correct idea.
• A piece is taken from the stem up to central region from the base of stem with the
help of increment borer instrument. The annual rings are counted from that piece
and again inserted (fitted) into the same stem at the same place