Secondary growth occurs in woody stems and roots through the activity of lateral meristems like the vascular cambium and cork cambium. This results in an increase in the stem or root diameter. The vascular cambium divides to produce secondary xylem internally and secondary phloem externally. In dicots, the vascular cambium forms a complete ring. As the stem grows in diameter, tissues inside like pith and medullary rays are compressed. The epidermis may rupture and be replaced by a protective periderm tissue like cork. Lenticels allow gas exchange through the impermeable cork layers. Secondary meristems also function in wound healing through wound cambium and cork formation.
The Shoot apex is also known as the terminal bud of plants that grows from 0.1-1.0 mm and consists of the apical meristem, developing leaves and the immediate surrounding leaf primordial. The shoot apex is present in both dicot and monocot plants.
Pollen pistil interaction
Types of Incompatibility in plants
Methods to overcome Incompatibility
Prepared by
Dr. T. Annie Sheron
Assistant Professor of Botany
DEPARTMENT OF BOTANY
KAKATIYA GOVERNMENT COLLEGE, HANAMKONDA
The Shoot apex is also known as the terminal bud of plants that grows from 0.1-1.0 mm and consists of the apical meristem, developing leaves and the immediate surrounding leaf primordial. The shoot apex is present in both dicot and monocot plants.
Pollen pistil interaction
Types of Incompatibility in plants
Methods to overcome Incompatibility
Prepared by
Dr. T. Annie Sheron
Assistant Professor of Botany
DEPARTMENT OF BOTANY
KAKATIYA GOVERNMENT COLLEGE, HANAMKONDA
It is called as “living fossil”
The whole order is extincted except one species Ginkgo biloba
This order was occurred in Triassic periods of Mesozoic age (200,000,000 years ago)
This order consists of 16 genera and many species (all in fossil forms except one)
Vascular Cambium & Seasonal activity & its Role in Stem & RootFatima Ramay
Vascular Cambium & Seasonal activity & its Role in Stem & Root:
The vascular cambium (pl. cambia or cambiums) is a lateral meristem in the vascular tissue of plants.
The vascular cambium is a cylindrical layer of cambium that runs through the stem of a plant that undergoes secondary growth.
In Dicots:
The vascular cambium is in dicot stems and roots, located between the xylem and the phloem in the stem and root of a vascular plant, and is the source of both the secondary xylem growth (inwards, towards the pith) and the secondary phloem growth (outwards).
In Monocots:
Monocot stems, such as corn, palms and bamboos, do not have a vascular cambium and do not exhibit secondary growth by the production of concentric annual rings. They cannot increase in girth by adding lateral layers of cells as in conifers and woody dicots.
Cambium of some plants remains active for the entire period of their life, i.e., cambial cells divide and resulting cells mature to form xylem and phloem elements.
This type of seasonal activity usually found in the plants present in the tropical regions, and not all plants show cambial activity.
Percentage of ringless trees in the rain forests of;India : 75%Amazon : 43%Malaysia : 15%
In regions with definite seasonal climate; seasonal activity of cambium ceased with onset of unfavorable conditions; In Autumn, it enters the dormant state and lasts for the end of summer; In Spring, cambium again becomes active.
Duration of cambial activity is also affected by day-length, e.g., In Robinia pseudoacacia, cambium is dormant under short-day condition.
The cambium cells formed in circular in cross section from the beginning onwards.
The cambial ring is partially primary (fascicular cambium) and partially secondary (interfascicular cambium).
Periderm originates from the cortical cells (extra stelar in origin).
In Dicot stem, for mechanical support xylem is with comparatively smaller vessels, greater fibers and less parenchyma.
More amount of cork is produces for protection.
Lenticels on periderm are very prominent.
The cambial ring formed is wavy in the beginning and later becomes circular.
The cambium ring is completely secondary in origin.
Periderm originates from the pericycle (intra stelar in origin).
In Dicot root, xylem is with big thin walled vessels with few fibers and more parenchyma.
Less amount of cork is produced as root is underground.
Lenticels on periderm are not very prominent.
A group of cells which are similar in Origin and function but of more than One type in structure.
Water conducting tissue
Along with phloem make vascular tissue
Provide support to plants
1)Tracheary elements
These are nonliving cells, provide support and conduct water. Two types,
(a)Tracheids: elongate, tube like cell, tapering, rounded or oval ends, hard lignified walls.
(b)Vessels members: long, cylindrical, tube-like structures with lignified walls.
(2)Fibres: thick walls, evolve from tracheids and provide mechanical strength. Two types,
(a)Fibre-tracheids: medium thickness walls, have reduced boardered pits.
(b)Libriform fibres: very thick walls, have reduced simple pits.
Parenchyma cells: living cells, in woody plants, store of food in starch form. Two types:
(a)Axial parenchyma: derived from fusiform initials, have tracheary elements and fibres.
(b)Ray parenchyma: derived from ray initials of cambium, xylem ray cells.
Developmentally, xylem have two types
(1)Primary xylem: derived from procambium, developing from embryo, non-woody plants.
(2)Secondary xylem: from vascular cambium, second stage of plant development, in woody plants.
the top three theories of root apical meristem in plants. The theories are: 1. Apical Cell Theory 2. Histogen Theory 3. Korper-Kappe Theory.The root apical meristem, or root apex, is a small region at the tip of a root in which all cells are capable of repeated division and from which all primary root tissues are derived. The root apical meristem is protected as it passes through the soil by an outer region of living parenchyma cells called the root cap.
The timing of cambial reactivation plays an important role in determination of the amount and quality of wood and the environmental adaptavity of trees.
Environmental factors, such as temperatures, influence the growth and development of trees.
Temperatures from late winter to early spring affect the physiological process that are involved in the initiation of cambial cell division and xylem differentiation in trees.
Cumulative elevated temperatures from late winter to early spring result in earlier initiation of cambial reactivation and xylem differentiation in tree stems and an extended growth period.
However, earlier cambial reactivation increases the risk for frost damage because the cold tolerance of cambium decreases after cambial reactivation.
A better understanding of the mechanisms that regulate wood formation in trees and the influence of environmental conditions on such mechanisms should help in efforts to improve and enhance the exploitation of wood for commercial applications and to prepare for climatic change.
Wood is the product of vascular cambium, and the formation of wood depends on the cambial activity of trees.
In temperate and cool zones, the vascular cambium of the stems of trees undergoes seasonal cycles of activity and dormancy, which are collectively known as annual periodicity.
This periodicity plays an important role in the formation of wood and reflects the environmental adaptivity of trees, for example their tolerance to cold in winter in cool and temperate zones.
The quantity and quality of wood depend on the division of cambial cells and the differentiation of cambial derivatives.
Cambial activity in trees is regulated by both internal factors, such as plant hormones, and environmental factors, such as, temperature, rainfall and photoperiod.
Temperature provides the appropriate physical conditions for the growth and development of trees in temperate and cool climates.
Timing of cambial reactivation is controlled by temperature, which influences both the quantity and quality of wood.
During the period from late winter to early spring, new cell plates are formed in the cambium and this springtime phenomenon is referred to as cambial reactivation.
It is called as “living fossil”
The whole order is extincted except one species Ginkgo biloba
This order was occurred in Triassic periods of Mesozoic age (200,000,000 years ago)
This order consists of 16 genera and many species (all in fossil forms except one)
Vascular Cambium & Seasonal activity & its Role in Stem & RootFatima Ramay
Vascular Cambium & Seasonal activity & its Role in Stem & Root:
The vascular cambium (pl. cambia or cambiums) is a lateral meristem in the vascular tissue of plants.
The vascular cambium is a cylindrical layer of cambium that runs through the stem of a plant that undergoes secondary growth.
In Dicots:
The vascular cambium is in dicot stems and roots, located between the xylem and the phloem in the stem and root of a vascular plant, and is the source of both the secondary xylem growth (inwards, towards the pith) and the secondary phloem growth (outwards).
In Monocots:
Monocot stems, such as corn, palms and bamboos, do not have a vascular cambium and do not exhibit secondary growth by the production of concentric annual rings. They cannot increase in girth by adding lateral layers of cells as in conifers and woody dicots.
Cambium of some plants remains active for the entire period of their life, i.e., cambial cells divide and resulting cells mature to form xylem and phloem elements.
This type of seasonal activity usually found in the plants present in the tropical regions, and not all plants show cambial activity.
Percentage of ringless trees in the rain forests of;India : 75%Amazon : 43%Malaysia : 15%
In regions with definite seasonal climate; seasonal activity of cambium ceased with onset of unfavorable conditions; In Autumn, it enters the dormant state and lasts for the end of summer; In Spring, cambium again becomes active.
Duration of cambial activity is also affected by day-length, e.g., In Robinia pseudoacacia, cambium is dormant under short-day condition.
The cambium cells formed in circular in cross section from the beginning onwards.
The cambial ring is partially primary (fascicular cambium) and partially secondary (interfascicular cambium).
Periderm originates from the cortical cells (extra stelar in origin).
In Dicot stem, for mechanical support xylem is with comparatively smaller vessels, greater fibers and less parenchyma.
More amount of cork is produces for protection.
Lenticels on periderm are very prominent.
The cambial ring formed is wavy in the beginning and later becomes circular.
The cambium ring is completely secondary in origin.
Periderm originates from the pericycle (intra stelar in origin).
In Dicot root, xylem is with big thin walled vessels with few fibers and more parenchyma.
Less amount of cork is produced as root is underground.
Lenticels on periderm are not very prominent.
A group of cells which are similar in Origin and function but of more than One type in structure.
Water conducting tissue
Along with phloem make vascular tissue
Provide support to plants
1)Tracheary elements
These are nonliving cells, provide support and conduct water. Two types,
(a)Tracheids: elongate, tube like cell, tapering, rounded or oval ends, hard lignified walls.
(b)Vessels members: long, cylindrical, tube-like structures with lignified walls.
(2)Fibres: thick walls, evolve from tracheids and provide mechanical strength. Two types,
(a)Fibre-tracheids: medium thickness walls, have reduced boardered pits.
(b)Libriform fibres: very thick walls, have reduced simple pits.
Parenchyma cells: living cells, in woody plants, store of food in starch form. Two types:
(a)Axial parenchyma: derived from fusiform initials, have tracheary elements and fibres.
(b)Ray parenchyma: derived from ray initials of cambium, xylem ray cells.
Developmentally, xylem have two types
(1)Primary xylem: derived from procambium, developing from embryo, non-woody plants.
(2)Secondary xylem: from vascular cambium, second stage of plant development, in woody plants.
the top three theories of root apical meristem in plants. The theories are: 1. Apical Cell Theory 2. Histogen Theory 3. Korper-Kappe Theory.The root apical meristem, or root apex, is a small region at the tip of a root in which all cells are capable of repeated division and from which all primary root tissues are derived. The root apical meristem is protected as it passes through the soil by an outer region of living parenchyma cells called the root cap.
The timing of cambial reactivation plays an important role in determination of the amount and quality of wood and the environmental adaptavity of trees.
Environmental factors, such as temperatures, influence the growth and development of trees.
Temperatures from late winter to early spring affect the physiological process that are involved in the initiation of cambial cell division and xylem differentiation in trees.
Cumulative elevated temperatures from late winter to early spring result in earlier initiation of cambial reactivation and xylem differentiation in tree stems and an extended growth period.
However, earlier cambial reactivation increases the risk for frost damage because the cold tolerance of cambium decreases after cambial reactivation.
A better understanding of the mechanisms that regulate wood formation in trees and the influence of environmental conditions on such mechanisms should help in efforts to improve and enhance the exploitation of wood for commercial applications and to prepare for climatic change.
Wood is the product of vascular cambium, and the formation of wood depends on the cambial activity of trees.
In temperate and cool zones, the vascular cambium of the stems of trees undergoes seasonal cycles of activity and dormancy, which are collectively known as annual periodicity.
This periodicity plays an important role in the formation of wood and reflects the environmental adaptivity of trees, for example their tolerance to cold in winter in cool and temperate zones.
The quantity and quality of wood depend on the division of cambial cells and the differentiation of cambial derivatives.
Cambial activity in trees is regulated by both internal factors, such as plant hormones, and environmental factors, such as, temperature, rainfall and photoperiod.
Temperature provides the appropriate physical conditions for the growth and development of trees in temperate and cool climates.
Timing of cambial reactivation is controlled by temperature, which influences both the quantity and quality of wood.
During the period from late winter to early spring, new cell plates are formed in the cambium and this springtime phenomenon is referred to as cambial reactivation.
This PPT contains a birds' eye view of the basic internal organization of the plant body comprising of tissue networks along with tissue systems to perform diverse functions for plants survival even in stress condition.
Gymnosperms definition
Morphological characters of Gymnosperms
Anatomy of Gymnosperms
Cycas
General character of cycas
Sexual reproduction in cycas
Asexual reproduction in cycas
Economical importance of cycas
Pinus
Characters of pinus
Sexual reproduction in pinus
Asexual reproduction in pinus
Importance of pinus
Roots anatomy
Stem anatomy
Xylem
Phloem
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2. Secondary Growth –
The growth which responsible for increase in height of plant is called primary
growth & produces primary tissues.
It is brought about by the activity of the meristems. The meristem which
involved in increase in height of plant either be apical or intercalary meristem.
These meristematic tissue responsible for primary growth of plant.
Many monocots & some herbaceous dicots possess only primary growth.
In Gymnosperms, woody as well as herbaceous dicots, & some monocots the
stem & root continue to grow, not only in length but also in diameter. This is
called secondary growth.
Secondary growth can be defined as production of secondary tissues by the
activity of the vascular cambium & cork cambium in the stelar & extra-stelar
regions leading to an increase in the girth of the stem or root. The vascular
cambium and cork cambium are also called as lateral meristem because they
present at lateral side of plant.
Complete secondary growth occur in two region ,stelar and extrastelar region .
3. Secondary growth in Dicot stem
Stelar secondary growth
Stelar secondary growth occur in plant due to vascular cambium . In plant there are two kind of
vascular cambium present inside stele i.e. interfascicular and fascicular cambium
Cambium which is located in between two vascular bundle called as interfascicular and cambium
present between xylem and phloem of single vascular bundle. Parenchyma cells which are a part
of the medullary ray & are in line with the fascicular cambium start becoming meristematic. Thus,
interfascicular cambium is formed.
Fascicular & interfascicular cambium now join hands to form a complete cambial ring.
The vascular cambium i.e., fascicular cambium is composed of two types of cells – the fusiform
initials & the ray initials.
The fusiform initials are elongated & spindle shaped & produce vascular tissues. The fusiform
initials are elongated tapering cells that give rise to all cells of the vertical system of the secondary
phloem and xylem (secondary tracheary elements, fibres, and sieve cells and the associated
companion cells).
The ray initials are smaller & isodiametric & give rise to the xylem & phloem rays. They
produce the vascular rays, which constitute the horizontal system of secondary tissues; this
horizontal system acts in the translocation and storage of food and water.
4. The cambial cells divide tangentially & produce secondary xylem on
the inner side & secondary phloem on the outer side.
The amount of secondary xylem produced is more than the amount of
secondary phloem.
Secondary xylem is composed of xylem vessels & fibres. There is less
of wood parenchyma.
Secondary phloem consists of sieve tubes, companion cells & phloem
parenchyma.
Due to increase in the girth, the cells of the non-vascular tissue, i.e.,
medullary rays, pith, hypodermis & cortex become tangentially
compressed.
The secondary tissues put pressure on the primary phloem lying
immediately outside & therefore it gets crushed.
T.S of Dicot Stem Showing normal growth
7. Extrastelar secondary growth
When a large amount of secondary tissues are produced in the stelar region,
the epidermis gets stretched & ultimately ruptures.
To protect the inner tissues, the epidermis is replaced by a new secondary
tissue called periderm.
The periderm consists of three layers which are meristematic in nature –
i) Cork cambium /Phellogen ,
ii)First cork cell /The phellem or cork produced by the phellogen
towards the outer side &
iii) The phelloderm or secondary cortex, a tissue that resembles cortical
parenchyma & consists of the inner derivatives of the phellogen.
Phellogen originates in the primary cortex through dedifferentiation. It is
reversion of permanent parenchymatous cells into meristematic cells.
8. The phelloderm is composed of cells that remain arranged in definite
radial rows. They help in storage of food.
Phellem or cork is composed of cells which are arranged in distinct
radial rows, without intercellular spaces & are without protoplasts at
maturity.
They are filled with either air or with highly coloured organic
substances which may be resinous or tanniferous compounds.
In the big perennial trees, the phellogen originates successively towards
the inner side.
The earlier formed phellogen does not function throughout the life but
is replaced by many successive phellogen layers.
This causes an accumulation of dead tissue on the outer side of the stem
& root.
Such composite periderm is called Rhytidome (shell bark). It consists
of cork, cortical layers & dead phloem placed alternately.
Bark is a non-technical term used to refer to all the tissues lying
outside the vascular cambium, but often used to designate the
phellem.
9. Kinds of bark
1. Ring Bark
Continuous bark of equal thickening is called ring bark.
It is formed around the stem in the form of a complete ring. In
ring bark cork cambium is continuous.
A complete distinct ring bark is formed in this plant. Its bark
was used as a writing material as a paper in ancient period.
Example: Bhojpatra (Betula utilis) and it is also formed in
Eucalyptus. Ring Bark In bhojpatra Tree
11. 2. Scaly Bark
Discontinuous bark of unequal thickening is called scaly
bark.
This bark is formed around the stem in the form of
pieces or fragments. In scaly bark the ring of cork
cambium is not continuous.
This scaly bark formed in Neem (Azadirachta indica),
Mango (Mangifera indica) and Imli ( indica) etc.
Scaly Bark is also formed in Neem
(Azadirachta indica)
13. Lenticels –
These are structurally differentiated portions of the periderm that are
characterized by relatively loose arrangement of the cells without any
suberization.
During periderm formation, gaseous exchange between the internal living
cells & the outer atmosphere becomes difficult; lenticels take over this
function of gaseous exchange.
Lenticels are first formed beneath the stomata. They originate either
before, simultaneously with or after the initiation of the periderm.
Parenchyma near the sub-stomatal chamber loses chlorophyll & divides in
many planes to form a mass of colourless cells with inter cellular spaces.
When phellogen is formed, it also produces the same type of loosely
arranged cells on the outer side instead of normal cork cells.
They increase in numbers & ultimately the epidermis ruptures & these
cells called complementary cells are exposed, forming a lenticel.
14. Functions of Secondary Meristem
1. Healing of wounds
When any plant part gets injured wound is formed there.
Boundary of the wound is raised outside and composed of similar type of living cells
(parenchyma) called callus.
Living cells of wound are responsible to form a cambium.
This is called wound cambium. It is also called inducible cambium.
This newly formed cambium forms cork towards the outside.
This cork covers the wound entirely. Wound cambium is lateral meristem.
15. 2. Abscission
Falling of any plant organ is called as abscission.
Abscission takes place due to formation of abscission layer at the
base of plant organ and it is composed of parenchyma.
Middle lamella is dissolved in abscission layer during abscission
and primary walls also dissolve partially or completely.
Sign of leaf fall on stem is called leaf scar and it is a type of
wound. The living cells of leaf scar are responsible to form cork
cambium, which produce cork.
Cork covers the wound. At the site of abscission protective layer is
found which is suberized.
16. 3. Knots
Knot is formed when branches are embedded inside the main stem. In most
cases knots are caused by the natural growth of the tree.
As a tree grows and increases the circumference of its trunk, the growing trunk
begins to overtake the branches that grow out from it. Knots form around these
branches, building up trunk material as the tree continues to expand.
The wood of the knot is typically tougher than the surrounding wood and may
form a bulge around the branch emerging from its center and known as tight
knot.
If a branch becomes injured or otherwise dies while still attached to the tree, a
loose knot forms as the trunk grows larger. Loose knots are similar to tight
knots, but instead of having living wood in the center of the knot there is only a
dark plug of dead or decaying material.