2. CONTENTS
• Introduction
• Ontogeny of secondary vascular tissues,
• Growth Rings,
• Heart wood,
• Types of Heart wood,
• Sap wood,
• Wood parenchyma
3. Introduction
In most dicotyledons and gymnosperms, the stems
increase in girth by the activity of lateral meristems.
A tree stem consists of three areas; pith, xylem and
bark. The central pith is usually bare visible and
does not increase in size through the life of the tree.
A cylinder of wood, known scientifically as xylem
ries in diameter with age and rate of growth. And
finally, the bark sheath can be subdivided into inner
bark and outer bark.
4. • New wood and inner bark are added each year
by the activity of a layer of dividing cells
sandwiched between the inner bark and
sapwood. New bark production is relatively small
compared with new wood production, and bark is
continually being shed to the outside of the stem,
thus in older trees the greatest volume of the
stem is wood. Since New wood is added to the
outside of existing wood the oldest wood is close
to the pith, and the most recent is close to the
bark.
5. Ontogeny of secondary vascular
tissues
• The initiaation of secondary vascular tissue occurs
after the maturation of primary xylem and
phloem. At this stage the cambium is represented
by a single layer of cells.
• The primary tissues lying outside the secondary
vascular tissues are subjected to pressure from
the inside by the enlarging secondary vascular
cylinder.
• The primary phloem is crushed and becomes non-
conducting.
6. • The cortex persists for a longer time as it increases
in circumference by cell division and cell
expansion.
• The epidermis may also persist through cell
division and cell enlargement to accmmodate the
diameter increase as the result of secondary
growth.
• However, in most plants with continued secondary
growth these outer tissues are completely crushed
by the formation of perdierm within them during
secondary growth. These dead peripheral layers
are eventually eliminated by decay or by
abscission.
7. Growth Rings
• The secondary xylem in the stems of parennial
plants commonly consists of concentric layers,
each one of which represents a seasonal
increment.
• In transverse section of the axis,these layers
appear as rings ,and are called annual rings or
growth rings.
• Each layer represents the growth of one year. The
width of growth rings varies greatly and depends
upon the rate of growth of tree.
8.
9. • In regions with a pronounced cold season, the
activity of the cambium takes place only during
the spring and summer seasons thus giving rise to
the growth in diameter of woody plants.
• In spring or sunmer the cambium is more active
and forms a greater number of vessels with wider
cavities. In winter ot autumn season,however
there is less need of vessels for sap transport,the
cambium is less active.
• EARLY WOOD:- The wood developed in the
summer or spring season is called spring wood or
early wood.
• Early wood is inner layer of growth rings. The
early wood zones of a growth rings typically
consists of thin walled, larger diameter cells and
also appear lighter in colour.
10. • Late wood:- The wood formed in winter or
autumn season is known as autumn wood or late
wood.Late wood is a outer layer of growth rings.
• Late wood zones thick walled , smaller diameter
cells and also appear darker or brownshade in
colour.
11.
12. • Dendrochronology:- Each annual ring corresponds
to one year's growth, and on the basis of these
rings the age of a particular plant can easily be
calculated. The determination of age of a tree by
counting the annual rings, is known as
dendrochronology.sometimes two annual rings
are formed in a single year, and in such cases the
counting of the annnual rings does not show the
correct age of the tree.this happens perhaps
because of the drought condition prevailed in the
middle of a growing.
13. • Tyloses:- In many plants, the walls of the xylem
vessels produce ballon like outgrowth into the
lumen of the vessels, are called Tyloses.
• Usually these structure are formed in secondary
xylem. Tyloses are formed by the enlargement of
the pit membranes of the half bordered pits
present in between a paranchyma cell and a
vessek or a tracheids.
14.
15. HEART WOOD & SAP WOOD
Sap wood Heart wood
The outer region of the old trees is
sapwood or alburnum.
The central region of the old tress
is called heart wood or duramen.
The sapwood consists of recently
formed xylem elements.
It is filled up with tannins,resins,
gums and other substances.
It is not hard and durable. It is hard and durable.
This is of light colour and contains
some living cells also in the
association of vssles & fibres.
It looks black or dark brown due to
the presence of various substances
in it.
Generally the vessels are not
plugged with tyloses.
Usually the vessels remain plugged
with tyloses.
16. This part of the stem performs the
physiological activities ,such as
conduction of water and
nutrients, storage of food etc..
The function of heart wood is not
of conduction, it gives only
mechanicak support to the stem.
17.
18. Types of heart wood
1) Ring-porous hardwoods: - for some groups of
species (oaks and elms) the earlywood/ latewood
transition occurs abruptly and is very distinct.
Within each growth ring, a band of large earlywood
vessels (pores) is clearly visible to the naked eye,
after which a band of latewood vessels appears
much smaller and requires the use of a hand lens to
see.
19.
20. 2) Semi-ring-porous hardwoods :- For another
group of species (black walnut, butternut and
hickory) the pore transition from large to small
diameter within a growth ring is gradual. The
pores in the earlywood zone have a largediameter
that gradually decreases in size as pores enter the
latewood zone.
21. • (3) Diffuse-porous hard woods :- the last group of
species has vessels (pores) that are uniform in size
across the entire growth ring (yellow poplar, gum and
maple). These vessels are usually small, uniform in size
and are very difficult to see with the naked eye (a hand
lens is needed).
22. • Ring porus heart wood also divided follow types:-
• Solitary pores : single pores that do not touch any other
pores evenly spaced across cross section (maples).
• Pore multiples : arrangement where two to five pores
appear grouped together.Pore multiples usually occur in
radial rows (cottonwood), but can occur in both radial
and tangential directions (Kentucky coffeetree).
• Pore chains : arrangement where pore multiples appear
in radial direction only.
• Nested pores : when larger numbers of pores contact
each other both radially and tangentially (cluster).
• Wavy bands : Pores are arranged in irregular concentric
bands. Also called ulmiform because this characteristic
is distinctive of all elms(also seen in strawberry)
23.
24. Sap wood
• Resin Canals :- The first step after making the
determination that a wood specimen is softwood
due to the absence of pores is to inspect the
cross-section surface for the presence of resin
canals. Resin canals are tubular passages in wood
that exude pitch, or resin, to seal off wounds that
occur due to insect or mechanical damage. Resin
canals most often occur in or near the latewood
zone of the growth rings. Softwoods can be
separated into two classifications based on the
presence or absence of resin canals.
25.
26. • Examples:- Species that have resin canals include
pines, spruces, larches and Douglas-fir. The species
that do not have resin canals include firs, hemlocks,
cedars, redwood, baldcypress and yew.
27. • Woods with resin canals are further separated
into two groups: (1) those with large resin canals
pines, and (2) those with small resin canals
Douglas fir, spruce and larch. Using a sample wood
identification set to compare the size and number
of resin canals of different species is useful in
determining how much they can differ between
species.
• For example, most pines have quite large and
numerous resin canals that can be seen without
the aid of a hand lens.
28.
29. Wood parenchyma
• Parenchyma are small, thin-walled, longitudinal cells
that provide food storage. These cells are sparse in
softwoods but are often quite significant in
hardwoods. Parenchyma are often very small and
difficult to see.
• However, there are many species with visible and
unique arrangements of parenchyma cells that offer
a clear structural feature for decisive identification.
30. • There are two basic types of parenchyma:
paratracheal and apotracheal.
• The major difference between them is that
paratracheal parenchyma make contact with the
pores or vessel elements, while apotracheal
parenchyma are separated from pores by fibers or
rays. In most species, apotracheal parenchyma are
not be useful in identifying wood with just a hand
lens. Paratrachal parenchyma appears in many
forms, and is often more useful for identification.
For example, in hickory the banded parenchyma
looks like a reticulate, Òweb-likeÓ formation as it
connects between the rays and pores. This Òweb-
likeÓ appearance is unique to hickory.
31.
32. References
• A Textbook of botany - Angiosperms
By :- B.P. Pandey
• http://wood
280.forestry.ubc.ca/files/2012/08/wood-anatomy.
• http://les.bf.uni-lj.si/fileadmin/datoteke-
asistentov/kcufar/english.
