Introduction
Wood isa Secondary Xylem tissue.
Wood is complex biological structure, a composite of many
chemistries and cell type acting together to serve the needs
of living plant.
Wood occurs in angiosperm and gymnosperm.
The term wood is applied to the secondary xylem formed
by vascular cambium during secondary growth.
Wood is hard and fibrous substance which forms a major
part of the trunk and branches of a tree.
4.
Structure of wood
It consists of a compact mass of thick-walled cells
arranged as: 1. Axial parenchyma, 2. Ray parenchyma
1. Axial parenchyma
The distribution of axial parenchyma is very
characteristic in dicotyledonous wood.
Parenchyma may lie independent of vessels or they may
be distinctly associated with them.
It is vertical and elongated and placed end-to-end
secondary xylem.
5.
It is derivedfrom fusiform cambial initials.
Axial parenchyma arranged longitudinal along the long
axis.
Each cell in a strand of axial parenchyma is usually
surrounded by a secondary by a secondary wall.
2. Ray parenchyma
Ray parenchyma cells vary in shape.
Ray cells that appear square in radial sections of wood are
called square ray cells modification of upright ray cells.
6.
Ray cells thatare composed only of either one type is
known as homocellular and the ray cells with both type is
known as heterocellular.
Angiosperm may have uniserate as well as multiseriate
rays which may range in height from one cell to many cell.
8.
Wood formation
• Woodformation (xylogenesis) comprises cell division, cell
expansion, secondary cell wall deposition, lignification and
finally programmed cell death, which occur in highly
coordinated and defined ways in response to the
environmental conditions imposed on the plant. In mature
tree stems, fusiform cambial initials give rise to fibres,
tracheids and vessel cells (only tracheids are formed in
conifers) while ray cell initials give rise to ray parenchyma
cells which, combined, form the ray system.
10.
Environmental Factors affectingWood Development
The processes of wood development are regulated by several
Intrinsic Factors, such as gene expression and hormonal signals,
together with Environmental Factors, such as temperature and
precipitation.
The Combined action of Intrinsic and Environmental Factors
is responsible for the unique structure of a tree ring formed at a
specific time in a specific position within the plant architecture.
The width of individual growth rings may vary greatly from year
to year as a function of such environmental factors as light,
temperature, rainfall, available soil water and length of the
growing season.
11.
Wood development issignificantly influenced by various
environmental factors, including light, water, and nutrient
availability. Research has shown that these factors can alter the
anatomical and physiological characteristics of wood, affecting
its growth and structure.
1. Light
•Light intensity plays a crucial role in wood development. High
light conditions generally promote greater vessel diameter and
shoot elongation, while low light can lead to reduced vessel
density and diameter. This variation in wood characteristics is
essential for optimizing photosynthesis and overall plant health.
12.
2. Water
•Water availabilitydirectly impacts wood growth. High
water levels can lead to broader vessels, enhancing the
plant's ability to transport nutrients and water. Conversely,
low water availability results in smaller vessel diameters,
which can restrict growth and wood production. The balance
of water is critical; excessive or insufficient water can both
negatively impact wood development.
13.
3. Temperature
Temperature playsa critical role in regulating growth and
cambial activity. Warmer temperatures can promote cell
division, cell-wall thickening, and increase cell production and
diameter, ultimately enhancing wood production.
4. Nutrients (Nitrogen and Phosphorus)
•Nutrient levels are vital for healthy wood development.
Adequate nitrogen and phosphorus are necessary for optimal
growth; low levels can reduce the amount of wood produced.
For instance, high nitrogen concentrations have been associated
with decreased wood production due to its effects on growth
dynamics.
14.
A research wasdone by David H. Arnold & James D.
Mouseth to know the effect of environmental factors on wood
development.
Experimental plants – Cereus (Genus)
Experimental factors – Light, Water, Nitrogen and
Phosphorus
Control plants received medium level of all factors.
Experimental plants received medium level of all factors
except experimental factors.
15.
Studies have demonstrateda strong correlation between
these environmental factors and wood formation across
different species.
In experiments involving Cereus peruvianus and Cereus
tetragonus, variations in light, water, nitrogen, and
phosphorus levels resulted in significant changes in vessel
characteristics and overall wood structure
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