This PPT intends to explore the basic idea of the secondary growth of the plant along its outcomes in connection with wood formation.

1. PLANT ANATOMY
.
By N.Sannigrahi, Associate Professor, Department
of Botany, Nistarini College, Purulia, 723101(W.B)
India

2. BEAUTY LIES INSIDE THE PLANT-EXPLORE IT

3. PRIMARY & SECONDARY GROWTH IMAGE

4. What is Secondary growth
• WHERE?

5. VASCULAR CAMBIUM IMAGE

6. NORMAL SECONDARY GROWTH
• Secondary growth as far as location takes place in two regions-
• Stealer Groth & Extrastealer Growth
• Stealer growth- Stele as you know the cental region of the tissue
ciomprising the pith, vascular bundle delimited by pericycle and
when secobdary growth takes place in that region called steaer
groiwth.
• Extrastealer growth- When the secondary growth takes place beyond
the stele, distributed in the outer part to be trweated as Extrastealer
growth.
• Both the two type of growth is soliciterd for the overall growth and
development of the plant by effective cell divisions, differentoatoio,
dedifferentiation and redifferentiastion called cyto differentation.

7. HOW DOES SECONDARY GROTH TAKE PLACE?

8. SECONDARY GROWTH IN DICOT STEM
• As you know, the dicot stem has conjoint, collateral and open type of Vascular
Bundle with exarch stem, in some cases the vascular bundle is bicollateral that
experiences another type of growth. The open vascular bundle is due to the
presence of camium that enables the secondary growth in dicot stem.
• It takes place in two regions-
• Intrastealer Growth-Within stele
• Extrastealer Growth-Outside stele
• INTRASTEALER GROWTH
• 1.A strip of procambium remains in between primary xylem and primary phloem
known as Intrafsciclar cambium making the VB as open for secondarey growth.
• 2. When the primary xylem and phloem are first differentiated, there is no
cambium across the pith rays or medullary rays to connect the edges of cambium
within vascular bundle.

9. PATHWAY FOLLOWS DURING SECONDARY GROWTH
• 3.As soon as the differentiation of of the first xylem and phloem of the bundles
take place, the cells of the pith or medullary rays which lie in between the edges
of the cambium within bundles divide accordingly and form a layer across the
medullary rays.
• 4. The newly formed cambium called interfasciclar cambium connects the
intrafascicular cambium and forms a complete cambial ring.
• 5.The cells of the cambium possess all the properities of meristenmatic cells-
Compactly set with little intercellular spaces, cell wall thin, rich cytoplasm,
cytoplasm contains less erserve food, eregastic subsrtances, large nucleus with
porplastid and vacuoles.
• 6. The cambium intially contain single layer cells and the cells divide in a
direction parallel with epidermis.Eacxh time, a cambial cells divides vin two, one
of the cells remain meristematioc-multiplicative in nature and other is
differentiated into permanent tissues
• 6. If the cell that is differentiated next to the xylem forms xylem and if it is next
to the phloem to form phloem.

10. PATHWAYS---------------------------------
• 7. In this manner, the cambium cells divide continuously in this manner
producing secondary tissues on both sides of it.
• 8. More cells of xylem sides than on the phloem side
• 9. The cells formed from the cambium in the region of pith rays become pith ray
cells.
• 10. The formation of new cvells from the cambium result in an enlargement of
the stem is known as secodary thickening in stealer rfegion.Ther primar phloem
occupies the peripheral position above the secondary phloem .
• The seconday xylem consists of scalriform and pitted vessel, tracheids, wood
fibres and wood parenchyma .
• With the passage of the time, yearly annual growth rings form due to secondary
xylem and this called annual rings.
• The branch of biology helps to determine the age of the plants by counting the
annual ring is called endroochronology.

11. AFTER SECONDARY GROWTH IN DICOT STEM

12. EXTRA-STELAR SECONDAREY GROWTH
• The considerable amount of secondary vasular tissues in the stlear region exerts
pressure developed within the stele and it is transmitted to the extrastelear region
when the epidermis ruptured, the cells of the cortex are crushed, the epidermis is
stretchedx and tends to be ruptured.So, to withstand the pressure, a special
protective tissues are formed usually replacing the peripheral tissues of stems.The
protective tissues are known as Periderm which is formed as a result of
extrastelear growth.
• In between the epidermis and cortex or phloem, some cells become meristematic
termed as phellogen or cork cambium.
• Unseriate, polygonal or rectangular in shape compactly set with little interc
ellular spaces.
• The cork cambium divides mainly tangentially oor less radially.
• The peripheral derivatives of cork cambium known as phellem-rectangular,
compactly set without intercellular spaces, 2-20 in rows form phellem or cork is
dead at maturity.The suberin, wax and the fatty substances make it impervious
but non-suberized cells occur in the phellem called Phelloids.

13. INSIDE A TREE TRUNK-AWESOME BEAUTY OF NATURE

14. WOOD-TYPES
• SPRING/ EARLY WOOD & AUTUMN /LATE WOOD
• In the temperate region, the wide fluctuation of temperature is visible in winter &
spring season.The wood of one season is markedly differ to the other season.In
spring or summer, the cambium is more active and forms a greater number of vessels
with wide cavities as the number of leaves increase.In winter or autumn season,
however, there is less need of vessels for sap transport, the cambium is less active
and gives rise to narrow vessel, trachids and wood fibres.
• The wood developed in summer or spring season is called spring wood or early wood
and the wood formed in the winter or autumn is called autumn wood or later
wood.Howver, the line of demarcation is quite conspicious between late wood of one
year and the early wood of the next year.An annual ring therefore consists of two
parts-an inner layer , early wood and an outer layer or late wood.
• In the age determination of plant, sometimes two annual rings are formed in a single
layer that make difficulty to determine the correct age of the plants.

15. ALBURNUM & DURAMEN
• SAP WOOD/ ALBURNUM & HEART WOOD/DURAMEN
• The outer region of the old trees consisting of recently formed xylem elements , light
in color, contains living cells also in the association of vessels and fibres with reserve
food to extend the physiological functions.It becomes proned to insects like teremites
to invade for food.This is called sap wood/alburnum.
• The central region of old trees formed earlier due to the actvity of vascular cambium
is filled up with tannins, resins, gums and other substances,and make it less prone to
insects, hard, durable, black in color .The vessels are plugged with tylosis.Such type
of more economical value containing wood used as timber.Haematoxylin is obtained
from the heart wood of Haematoxylon campechianum is an important constituents in
industrial purposes.
• The proprtion of sap woods and heart woods variable.Some trees do not have clear
distinction-Poplus, Salix, abies whereas other possess sap wood like Morus, taxus etc.

16. PERIDERM-BARK
The cork or suberized tissue present at the periphery of the stems and roots originates
from the secondary lateral meristem or phelloogen is known as bark or periderm.The
periderm consists of three parets-
- a meristem known as phellogen or cork cambium
-the layer of cells cut off by phellogen on the outer side known as phellem or cork,
-the layer of cells cut off by phellogen towards inner side is known as phelloderm.
The periderm apopears on the surface of the plant parts that possess a continous
increase of thickness by secondar gowth.
Commercial cork-The development of the periderm layersd in the cork oaks (Quercus
suber) s of special interest.The abil;ity of the plant produce phellogen in deeper layers
when the periderm is removed and produce massive cork of better quality than the first.
Phelloderm very often termed as secondary cortex like the other tissues.

17. DEVELOPMENT OF PERIDERM

18. PERIDERM

19. RHYTIDOME & LENTICELS
In most of the plants, as soon as the first phellogen ceases to function, second phellogen
develops in the tissue below the first one.In this way, additional layers of periderm are
formed progressively deeper regions of stem, thus new phellogen layers arise in deeper
regions of the cortex which may exceed even upto phloem.As ther phellogen arises in
deeper regoion and cuts cork cells or phellem towards outside, all the living cells ouside
the phellogen do not get water supply and become dead.These dead tissues formed
outside the phellogen constitute rhytidome.
LENTICELS
In the periderm of most of the plants. Certain areas with loosely arranged cells
undergone breakage and the broken areas are called lenticels.A lenticel is thus a small
portion of the periderm where the actvity of the phellogen is more than elsewhere, and
the cork cells produced by it are loosely arranged and possess intercellular spaces.As
the lenticels are formed, the parenchyma cells lose their chlorophyll and divide
irregularly giving rise to a mass of colorless, rounded , thin walled cells called
complementary cells.

20. LENTICELS

21. RHYTIDOMES

22. TYLOSIS & TYLOSOIDS
• TYLOSIS
• In many plants, the walls of the xylem vessels produce ballon like outgrowths into
the lumen of the vessels are called tylosis.Usually, the structures are formed in the
secondary xylem but they may also develop in the primary xylem vessels.Tylosis are
formed by the enlargement of the pit membranes of the half bordered pits present in
between a pasrenchyma cell and a vessel or tracheid.Usually they are sufficiently
large and the lumen of the vessel is blocked.The nucleus of the xylem parenchyma
cell along with the cytoplasm passes into this ballon like outgrowth.The delicate pit
membranes forms the ballon like tylosis inside the lumen cavity. They are commonly
found in the different angiospermic famiilies to add durability.e.g Cucrbita,
Rumex.etc
• TYLOSOIDS
• In the wood of conifers, the closing of the cavity of resin canals by the enlargement
of epithelial cells are termed as tylosoids.

23. TYLOSIS IMAGE

24. RING POROUS WOOD VS DIFFUSE POROUS WOOD
• Hard woods may be divided into -ring porous and diffuse porous wood.
• In ring porous wood, the vessels laid down at the begining of the growing season are
much larger than subsequent vessels laid down at the end of the sason(ring). diffuse
porous trees form vessel of roughly same radial diameter throghout their life span.
• RING POROUS:
• i. Vessels are of different diameter,
• ii. Vessels are not uniformly distributed,
• iii.Vessels with wide and smaller diameter are foirmed in the early and later part of
the groth season respectively.
• iv.The developmen t of vessel is sudden and rapid.
• DIFFUSE POROUS WOOD
• i.Vessels areew more or less equal in diamter
• ii.Vessels are uniformly distributed throghout the wood
• iii.The vessels are shorter in length.

25. RING POROUS & DIFFUSE POROUS WOOD

26. HARD WOOD VS SOFT WOOD
CHARACTERS HARD WOOD SOFT WOOD
Definition Mostly dicots having broad leaves, vessel
elements to transport water, pores abundant
Comes from gymnosperm having
needles and cones, medullary
rays and tracheids transport water,
no visible pores beacuse of
tracheids
Uses High quality furniture like decks, flooring windows, doors, medium size
fibre board, paper, christmas trees
Examples Alder, Balsa, Maple, Oak, Teak, mahagony,
Beech, Walnut
Cedar, Fir, Juniper, Pine, spruce,
redwood
Density Higher Lower density
Growth Slower growth Faster growth
Shedding of leaves Shed their leaves No shedding of leaves
Fire resistence More Poor

27. SECONARY GROWTH IN DICOT ROOT
• Radial vascular bundle with exarch protoxylem are the characteristic of
roots.Primary xylem & primary phloem lie in separate and alternate to each other.In
dicot roots, secondary tissues are formed both at intrastelar and extrastelar
regions.Intially, the primary vascular bundles appear closed one but soon after, the
seconadry growth takes place.
• HOW DOES IT TAKE PLACE?
• The secondary growth restricted in two regions: Extrastelar & Intrastelar region.
• INTRASTELAR REGION:
• It takes place by the secondary cambium as the primary cambium remains absent.
The entire process of the secondary growth in the intrastelar region takes place by the
following sequences.

28. PLANT-ROOT & GROWTH

29. STEPS OF SECONDARY GROWTH
• Secondary cambium originates from the permanent tissues present in the stele.
• i. Strips of cambia differentiate below each primary phloem.
• ii. Cambia are also formed above the protoxylem , near or at the pericycle.
• iii. These strips of cambia extend laterally and join eacxh other.
• iv. As a result, a wavy cambium ring with ridges and furrows appear.
• v. The ridges lie overarching the protoxylem whereas the furrows are present below
the primary phloem.
• vi. So, according to the number of xylem and phloem present in the stele, the number
of ridges and furrows appear.
• vii. The wavy cambium ring divides in all segments and produces secondary tissues
at the peripheral and inner side.
• viii.The peripheral derivatives are differentiated into secondary phloem while
secondary xylem is formed from the inner cells.

30. SECONDARY GROWTH

31. STEPS OF SECONDARY GROWTH
• ix.Normally, the cambial cells at the furrowed region divide more in contrast to the
ridges zone.The camium ring becomes more or less circular and lies in between the
seconadry xylem and phloem.Usually, more Seconady xylem is differentiated than
Seconadry phloem like stem.All elements of xylem & phloem components are
differentiated in the secondary vascular tissues.
• PERIDERM FORMATION DUE TO EXTRASTELAR GROWTH
• Soon after the formation and division of vascular cambium, some cells of the
pericycle becomes meristematic. As a result, another cambium is formed-Cork
cambium or Phellogen.Like stem, the phellogen derivatives vin the peripheral region
differentiated into phellem or cork cells where as inner cells form Phelloderm.after
the differentiation of periderm all tissues, which lay outside the cork , die.They are
ultimately sloughed off. Periderm is protective in nature and impervious to air and
water. Sometimes, lenticels may appear. The exarch protoxylem pushed towards the
centre cofirms the root nature.

32. PRIMARY & SECONDARY GROWTH

33. CONCLUSION
• So, from the above presentation, it has been quite clear that the plant after having the
pleasure of the primary growth, the seconadry growth takes place in order to address
the growing needs of the physiological conditions to the body along with to develop
some features in order to adapt itself in the emerging ecological coditions.In addition
to these normal secondary growth in aerial and underground portion of the plants,
some abnormal secondary growth also take place that to be explored in our next
academic meet. Until, that thanks a lot for your patience to listen me.
• THANKS A LOT