Plant Anatomy (re-edited)

Plant anatomy

• Meristematic tissues: structure, classification (origin, position, and function), apical meristem theories (histogen, tunica-corpus)
• Permanent tissues: simple, complex, and secretory tissues

Plant tissue system

• Tissue: group of cells alike in origin and structure, performing a specific function.
• Two types of plant tissues:
  • Meristematic tissues
  • Permanent tissues

Meristematic tissues

Origin & Development

• Promeristem
• Primary meristem
• Secondary meristem

Location

• Apical
• Intercalary
• Lateral

Function

• Protoderm
• Procambium
• Ground meristem

Permanent tissues

Simple

• Parenchyma
• Collenchyma
• Sclerenchyma

Complex

• Xylem
• Phloem

Meristematic Tissue

• Immature, young, undifferentiated cells with continuous division potential, commonly called meristem.
• Present in root and shoot apex.
• Assist in the growth in length and diameter of the plant.

Characteristics:

1. Living cells with continuous division capability
   • Carl Wilhelm von Nägeli coined the term "meristem".
2. Undifferentiated, young, and immature cells
3. Oval, rounded, polygonal, or rectangular shape
4. Compactly arranged without intercellular spaces
5. Thin cell wall made of Cellulose, enclosing dense protoplasm
6. Single, large, and prominent nucleus
7. Very small and few vacuoles
8. Do not store food but exhibit high metabolic activity
9. Heal wounds of an injured plant

Types of Meristematic Tissue

Classified based on origin, position, and function in the plant body.

Based on Origin:

1. Promeristem (primordial meristem)
2. Primary meristem
3. Secondary meristem

Promeristem:

• Embryonic in origin.
• Earliest and youngest meristematic tissue in growing root and shoot tips.
• Gives rise to primary meristem.

Primary Meristem:

• Arises from promeristem.
• Cells are always active and dividing.
• Present below promeristem in shoot and root tip, and in intercalary position.
• Gives rise to secondary meristem and primary permanent tissue.

Secondary Meristem:

• Arises from primary meristem.
• Develops later in life.
• Gives rise to secondary permanent tissue.

Based on Position:

1. Apical meristem
2. Intercalary meristem
3. Lateral meristem

Apical Meristem:

• Present at apical parts of the plant, such as root and shoot tips.
• Helps in increase in height of plants.
• Two distinct zones:
  • Promeristem zone: contains dividing cells (apical initials).
  • Meristematic zone: contains protoderms (epiderm), procambium (primary vascular tissue), and ground meristem (cortex and pith).

Intercalary Meristem:

• Present in intercalary position in the leaves and internode.
• A part of apical meristem.
• Adds to the height of plants.
• Commonly present in monocots, grass, and pines.

Lateral Meristem:

• Present on the lateral side of the stem and root.
• Helps in increasing the diameter or thickness of plants.
• Examples: vascular cambium (primary meristem) and cork cambium (secondary meristem).

Based on Function:

1. Protoderm
2. Procambium
3. Ground meristem

Protoderm:

• Outermost meristematic tissue.
• Gives rise to epidermis, providing protection from mechanical injury.

Procambium:

• Innermost meristematic tissue.
• Gives rise to vascular tissue (xylem and phloem).
• Transports water and nutrition.

Ground Meristem:

• Gives rise to cortex, endodermis, pericycle, and pith in dicots and hypodermis, ground tissue in monocots.
• Performs various functions.

Theories of Meristematic Tissues

Proposed to explain the origin of apical meristem.

1. Histogen Theory
2. Tunica-Corpus Theory

Histogen Theory

• Proposed by Hanstein in 1868.
• Histogen means tissue builder.
• Tissues of a plant body originate from a mass of meristem where three histogens can be distinguished:
  • Dermatogen
  • Periblem
  • Plerome

Dermatogen:

• (In Greek meaning skin).
• Outermost layer of the meristem.
• Gives rise to the epidermis of the root and stem.

Periblem:

• (In Greek meaning clothing).
• Internal to dermatogen but peripheral to plerome.
• Forms the cortex of root and shoot and inner tissues of leaves.
• Surrounds plerome.

Plerome:

• (In Greek meaning that this fills).
• Gives rise to the vascular cylinder of stem and root and pith.
• Central core of stem and root.
• Cells are enveloped by dermatogen and periblem.

Demerits of Histogen Theory:

1. No clear demarcation between Periblem and Pleurome in Gymnosperms and Angiosperms.
2. The roles of three Histogens is not demonstrated.

Tunica-Corpus Theory

• Proposed by Schmidt in 1924 based on studies of shoot apices of angiosperms.
• Applicable only to the shoot.
• Two zones of Apical meristem: Tunica and Corpus.

Tunica:

• Outer zone.
• One or more peripheral layers of small uniform cells that divide anticlinally (perpendicular to the surface).
• In Dicots: 1 to 5 layered, in Monocots: 1 to 4 layered.
• Responsible for surface growth in the apex as a sheet but not in thickness.
• To increase in thickness, it has to divide periclinally (rare).
• Two cytological zones recognized:
  • Central apical zone
  • Zone between central apical zone and leaf primordium

Corpus:

• Inner zone of shoot apex.
• Composed of undifferentiated mass of larger cells enclosed by Tunica.
• Divides in all planes to increase the volume of the shoot apex.
• Gives rise to the cortex and vascular tissue.
• Consists of several zones:
  • Central mother cells: Uppermost zone of Corpus.
  • Pith rib meristem: Occurs below the Central mother cell zone.
  • Flank meristem: Surrounds both Central mother zone and pith rib meristem.

Merits of Tunica Corpus Theory:

• Deals with planes of cell division, description of meristem becomes precise.
• Explains growth pattern clearly in shoot apex of Angiosperms.
• Enables understanding of leaf development as they arise close to the apex.
• Specific variation of the number of Tunica layers may be of Taxonomic importance (e.g., in Grass).
• Has topographical value in the study of the development of different tissue systems in plants.
• The destiny of derivatives of the corpus is not predetermined.

Permanent Tissue

• Differentiated, mature cells that have lost the ability of division.
• Two types:
  • Simple permanent tissue
  • Complex permanent tissue

Simple Permanent Tissue

• Composed of a group of identical cells (homogeneous) performing a common function.
• Divided into three categories:
  1. Parenchyma
  2. Collenchyma
  3. Sclerenchyma

Parenchyma

• Living simple permanent tissue present in almost all parts of the plant.
• Examples: pith and cortex of stems and roots, mesophyll of leaves, reproductive cells (spores, gametes), the flesh of succulent fruits, endosperm of seeds, along with other tissues like Xylem and Phloem.

Structure of Parenchyma Cells

• Living, simple permanent tissue.
• Isodiametric or polyhedral in shape (polygonal, oval, round, or elongated).
• Closely packed or may have small intercellular spaces.
• Thin cell wall made of cellulose, hemicelluloses. Plasmodesmata join the cells.
• Cell wall encloses prominent nucleus, protoplast, and small vacuoles.

Types of Parenchyma Cells

Categorized based on structure, location, and functions performed.

• Chlorenchyma
• Vascular parenchyma
• Storage parenchyma
• Prosenchyma
• Aerenchyma
• Epidermis parenchyma
• Conjunctive parenchyma

1. Chlorenchyma: Cells with chloroplasts that perform photosynthesis.
   • Examples: mesophyll cells in leaves (palisade and spongy cells), green stems, sepals, areas of absorption and secretion (nectaries), carnivorous plants.
2. Vascular Parenchyma: Parenchyma cells associated with vascular tissues.
   • Phloem Parenchyma: Elongated cells with dense cytoplasm, absent in monocotyledons.
   • Xylem Parenchyma: Thin-walled cells.
3. Storage Parenchyma: Store substances like water, starch, proteins etc.
   • Act as a food and water reservoir.
   • Stored protein: a source of nitrogen.
   • Starch: in potato tubers, the endosperm, amyloplasts.
   • Water storage: in succulents such as Cactaceae.
4. Prosenchyma: Thick-walled fiber-like elongated cells that provide rigidity and strength to the plant.
5. Aerenchyma: Contain very large intercellular spaces filled with air.
   • Help in buoyancy in floating hydrophytes.
6. Epidermis Parenchyma: Found in the epidermis of the leaves of some gymnosperms.
   • Have cutinised cell walls, reducing transpiration.
7. Conjunctive Parenchyma: Present in the root system.

Functions of Parenchyma cells

• Storage: Large intercellular space for storage.
• Transport: Transport nutrients and other chemicals.
  • Xylem parenchyma: helps in radial transportation of water and minerals.
• Photosynthesis: Chlorenchyma with chloroplasts performs photosynthesis.
• Gas Exchange: Aerenchyma cells facilitate gas exchange and floating (buoyancy) in aquatic plants.
• Protection: In gymnosperms, parenchymatous cells have spiny projections for protection from predators.
• Totipotent: Ability to transform into other types of cells and act as a precursor for other types of cells.
• Healing and regeneration: Parenchyma cells regain their ability to divide on maturity, help in regeneration and wound healing.
• Tyloses: Tyloses present in the xylem parenchyma help in preventing damage to vascular tissues in the condition of drought.

Collenchyma

• Living, flexible, and mechanical,simple permanent tissue.
• Found in the pedicel, petiole, peduncle, epidermis, and the vascular bundle of dicot leaf.

Structure of Collenchyma

• Living, mechanical,simple permanent tissue.
• Each cell is elongated, unevenly thick-walled.
• Intercellular space: may be present or absent.
• Cell wall made of cellulose and pectin in intercellular space.
• Encloses vacuolated cytoplasm and prominent Nucleus.
• The amount of chloroplast is less in the cells.
• The cells have no intercellular spaces.

Types of collenchyma tissue

Classified based on deposition of Hemicellulose and Pectin in cell wall into 3 types.

1. Angular collenchyma: thick cell wall at the corner of the cell; without intercellular space
2. Lacunar collenchyma: thick wall at the border of the cell; large intercellular space
3. Plate or lamellar collenchyma: thick wall at tangential wall; without intercellular space.

Functions of collenchyma

1. Provides mechanical support and elasticity to the stems of dicot plants.
2. Cells possess chloroplast; then, it is involved in manufacturing sugar and starch.
3. Provides tensile strength and flexibility to the plant body.

Sclerenchyma

• (Gr.scleros, hard + enchyma, infusion, in reference to the infusion of lignin in the secondary cell walls)
• Dead, mechanical simple permanent tissue.
• Present in the stem, covering of seeds, nuts, around the veins of the leaves, around vascular bundles.

Structure of Sclerenchyma:

• Dead mechanical, simple tissue present in Pericarp, seed coatwhich makes the plant hard and stiff.
• Cells have extremely thick cell walls( secondary wall) lignified ( The walls of the cell are thick due to the presence of lignin.)
• Composed of elongated cells pointed at both end.
• Cells lack protoplasm.
• Cell wall encloses an empty cavity called 'Lumen'.
• Sclerenchyma gives strength and rigidity to the plant body.

Types of sclerenchyma tissue

Sclerenchyma is composed of 2 types.

1. Fibres
2. Sclereids

• Fibres

  • Thick walled, elongated, spindle shaped cells with pointed tips.
  • Cell wall enclosed narrow lumen with simple rounded pits and lignified secondary wall
  • Distributed in cortex, pericycle, xylem and phloem
  Types of Fibres:
  • Surface fibres: found on fruit wall and seed coat (e.g., coconut)
  • Xylary or Wood fibres: associated with xylem
  • Extraxylary or Bast fibres: seen associated with cortex, pericycle and phloem
  Function of Fibres:
  • Provide mechanical support to the plant parts
  • Surface fibres help in seed and fruit dispersal

• Sclereids (stone cell):

  • Extremely thick walled cell with spherical, oval or dumbbell shape.

  • Cell wall contains simple pits

  • Present in hard part of plants, pulp of fruits

  • Provide local mechanical support

  • Classified based on their shapes as follows:-

    1. Stone cells:- The sclereids are isodiametric and resemble parenchyma cells.,commonly known as stone cell due to hard walls. Ex: Flesh of fruits of Pyrus, Cinnamomum stem.
    2. Macrosclereids: Macrosclereids are rod like scklereids present in bark and seed coat of Leguminous plants.
    3. Osteo sclereids: The osteosclereids are columnar,the end may be lobed or branched or simply enlarged like a narrow bone, e.g. the seed coats of Pisum, the leaves of Hakea etc.
    4. Astro sclereids: Astro sclereids are stellate cell( deeply lobed or branched),resembles stars, e.g. leaves of Thea (tea),petiole of Nymphaea etc.
    5. Filiform sclereids: Filiform sclereids are hair like elongated cell with branches, which extends into the intercellular spaces, e.g. leaves of Olea, Nymphaea, and aerial root of Monstera etc.
  Function of Sclereids:
  • Mechanical cells and support the tissues in which they occur.
  • Sclereids, form a continuous layer at the periphery, protect the inner tissues.
  • It makes the plant body rigid, flexible, and elastic.
  • Provides hardness to stony fruits such as nuts, coconut, almond, etc.

The difference between the three simple tissues

Complex permanent tissue

• Heterogeneous in nature, being composed of different types of cell elements.
• Xylem and phloem are the complex tissues which constitute the component parts of the vascular bundle.
• They are also called vascular tissues.
• These are the two most important complex tissues in a plant, as their primary functions include the transport of water, ions, and soluble food substances throughout the plant.

I.Xylem (also known as wood)

• A complex tissue forming a part of the vascular bundle.
• Primary xylem originates from the procambium of apical meristem, and secondary xylem from the vascular cambium
• The function of xylem is to transport water and minerals from the root to the leaves of plants.
• It also provides mechanical support to plants.
• Xylem is composed of four types of cells-Tracheids, Vessels, Xylem fibres and Xylem parenchyma.

Components of Xylem (Elements of Xylem):

Xylem is composed of 4 elements (Components).

1. Tracheids- Dead component.
2. Tracheae or vessels - Dead component
3. Xylem fibres, called xylem fibres or wood fibres - Dead component
4. Xylem parenchyma, referred to as xylem or wood parenchyma – living component

1) Tracheids (Dead component).

• An elongate cell occurring along the long axis of the organ. The cells are devoid of protoplast, and hence considered as dead component.
• Tracheid has a cavity, lumen without any contents and tapering blunt ends.
• Tracheids are round or polyhedral in cross-section.
• Tracheids are most primitive and fundamental element in xylem element found in the fossils of seed-plants. In modern plants they occur predominately in lower vascular plants, the pteridophytes and gymnosperms.
• The wall is hard, thick and lignified.
• Secondary walls are deposited in different manners, so that the tracheids may be annular, spiral, reticulate, scalariform or pitted.

2) Tracheae( vessels)

• Vessel or a Trachea originates from a row of meristematic cells of procambium or vascular cambium which remain attached end on end in longitudinal series
• They do not occur in some xerophytes, parasites and aquatic plants.
• Trachea or vessel is formed from a row of cylindrical cells arranged in longitudinal series like a tube.
• Perforations are present in end-walls, may rarely occur on the lateral walls
• The vessels have distinct 'perforate' bodies which makes translocation of solutes easy.
• Perforations remain either in more or less parallel series like bars called scalariform perforation or in form of a network known as reticulate perforation, or even may form a group of circular holes (foraminate perforation). The perforation occurs in form of a single large circle, referred to as simple perforation
• Elements are devoid of protoplast and have hard and lignified cell-wall with different types of localised thickenings such as ring-like, spiral, scalariform, reticulate or pitted. The pits are mostly of bordered types.
• Transport of water and solutes, and, secondarily, for mechanical support.

3) Xylem Fibres:

• Sclerenchyma fibres remain associated with other elements in xylem.
• They give mechanical support.
• Fibres are very much elongated, dead cells with lignified walls.
• Xylem fibres or wood fibres are mainly of two types: fibre-traeheids and libiriform fibres.
• Fibre-tracheids are intermediate forms between fibres and tracheids, possess bordered pits,
• Libiriform fibres are narrow with highly thickened secondary wall.

4) Xylem Parenchyma:

• Xylem Parenchyma is a living parenchyma associated with other xylem elements
• The cells may be thin-walled or thick-walled. If lignified secondary wall is present.
• These are meant for storage of starch and fatty food; Tannins, crystals, etc., may also be present.

Phloem (Bast and leptome)

• Phloem is a complex tissue forming a part of the vascular bundle Phloem originate from the procambium of apical meristem or the vascular cambium.
• It is meant for translocation of organic solutes - the elaborated food materials in solution.

It is composed of

1. Sieve elements
2. companion cells
3. PhloemParenchyma
4. Phloem fibres.

1) Sieve Elements:

The constituents of phloem sieve elements is composed of a)sieve tubes and b)sieve cells.

• Sieve tubes are long tube-like structures formed arranged in longitudinal series.

• The end-walls of Sieve tube are perforated in a sieve-like manner. The perforated end-walls are called the sieve plates. Through which cytoplasm connections are established between adjacent cells.

• Sieve plate is called simple, if it has only one sieve area, Sieve plate is compound, if it has several sieve areas arranged in scalariform, reticulate or other manners.

• Sieve cells are more primitive than the sieve tubes.

• They occur in lower vascular plants and gymnosperms.

• Sieve cells are narrow elongated cells without conspicuous sieve areas.But with inclined walls.

• They originate from the mother cells which are usually short cylindrical or elongate ones.

2) Companion Cells:

• Companion cells occur abundantly in angiosperms, particularly in the monocotyledons. They are absent in some primitive dicotyledons.
• The procambial mother cell divides longitudinally into two daughter cells, one of which serves as the sieve element and the other one becomes the companion cell. Hence companion cell is considered as Sister cell to sieve tube.Companion cells remain associated with the sieve tubes of angiosperms,
• These are smaller cells, having dense cytoplasm and prominent nuclei without Starch grains.
• The wall between the sieve tube and companion cell is thin and provided with primary pit fields.
• Controls the activity of sieve tube.
• In transverse section it appears as a small triangular, rectangular or polyhedral cell with dense protoplast.

3) Phloem Parenchyma:

• Parenchyma cells associated with sieve elements are referred as Phloem Parenchyma.
• It is absent in the phloem of monocotyledons.
• These are elongated cells and occur with the sieve elements along the long axis
• These are living cells with cellulose walls having primary pit fields.
• In secondary phloem they may be of two types. namely
  • phloem parenchyma-It occurs in vertical series and
  • Ray cells-It occurs in horizontal planes.
• They are meant for storage of organic food matters. Tannins, crystals etc.

4) Fibres:

• Sclerenchymatous fibres associated with phloem is referred as Phloem fibres or Bast fibres.
• They are rare in pteridophytes and some spermatophytes.
• These fibres are used for the manufacture of ropes and cords. Provides mechanical strength to the plant.

Structure of Dicot & Monocot Root, Stem and Leaf.

Structure of Dicot & Monocot Root

• A typical Angiosperm is distinguished into 2 parts.
  1. Root system
  2. Shoot system

I.Root system:

• Root system is an underground, non green descending organ of the plant developed from Radicle part of an embryo.
• It is positively geotropic, positively hydrotropic.
• Perform function of Anchorage, absorption and conduction.

Types of Root system.

1. Tap root system
2. Fibrous root system.

1) Tap root system: Ex: Dicot plants

• In Tap root system Radicle develops into single, central main root called 'Primary root'.

• It develops lateral secondary roots which in turn branches to form tertiary and quaternary roots.

• Lateral roots bear unicellular root hairs which take part in absorption of water and mineral nutrients from soil.

• Taproot grows deep into the soil and persists throughout life of the plant.
  2) Fibrous root system: - Ex: - Monocot plants.

• In Fibrous root system Radicle develops into primary root.

• It is short lived and soon replaced by cluster of slender, fibre like root.

• They bear root hairs which help in absorption.

• Fibrous root does notgrow deep into the soil (Surface feeders), and they are periodically renewed.

Study of Anatomy of Root

Anatomy of Dicot root. EX:-Cicer root

Transverse section of Cicer root shows following Anatomical features:-

1. Epiblema
2. Cortex
3. Stele

1) Epiblema: Epiblema is the outermost layer of Root.

• It is consists of single layer of compactly arranged, rectangular, thin walled cells.

• Some of the cells develop into unicellular, tubular cells called 'Root hair'.

• It is meant fro absorption.
  2) Cortex: Cortex is composed of many layers of Parenchyma cells with intercellular spaces.

• Endodermis is innermost layer of the cortex. It consists of single layer of barrel shaped cells with casparian strips on their radial walls.

• Few endodermal cells opposite to ProtoXylem are thin walled called 'Passage cells".
  3) Stele: Stele is composed of Pericycle, Vascular bundle, Conjunctive tissue and Pith.

• Pericycle: Pericycle is the outermost layer of stele present next to endodermis. It is made up of single layer of parenchyma cells.

• Vascular bundle: - Vascular bundle is Radial, Tetrarch and Exarch.(Radial-Xylem and Phloem are present alternately at different radii, Tetrarch- There are 4 patches of Xylem alternating with 4 patches of Phloem,Exarch- Protoxylem is present towards pericycle and Meta Xylem towards Pith.)

• Conjunctive tissue: - Parenchyma tissue present between Vascular bundle is called 'Conjunctive tissue'.

• Pith:-Central region of stele made up of parenchyma tissue is constitutes 'Pith'. It is small.

Anatomy of Monocot root. EX:-Canna root

Transverse section of Canna root shows following Anatomical features:-

1. Epiblema
2. Cortex
3. Stele

1) Epiblema: Epiblema is the outermost layer of Root.

• It is consists of single layer of compactly arranged, rectangular, thin walled cells.

• Some of the cells develop into unicellular, tubular cells called 'Root hair'.

• It is meant fro absorption.
  2) Cortex: Cortex is composed of many layers of Parenchyma cells with intercellular spaces.

• Endodermis is the innermost layer of the cortex. It consists of single layer of barrel shaped cells with casparian strips on their radial walls.

• Few endodermal cells opposite to Proto Xylem are thin walled called 'Passage cells".
  3) Stele: Stele is composed of Pericycle, Vascular bundle, Conjunctive tissue and Pith.

• Pericycle: Pericycle is the outermost layer of stele present below endodermis. It is made up of single layer of parenchyma cells.

• Vascular bundle: - Vascular bundle is Radial, Polyarch and Exarch.(Radial-Xylem and Phloem are present alternately at different radii, Polyarch- There are many patches of Xylem alternating with equal number of Phloem Patches,Exarch- Protoxylem is present towards pericycle and Meta Xylem towards Pith.)

• Conjunctive tissue: - Parenchyma tissue present between Vascular bundle is called 'Conjunctive tissue'.

• Pith:-Central region of stele made up of parenchyma tissue is constitutes 'Pith'. It is very large.

Differences between Monocot and Dicot root:-

Shoot system

• Shoot system is an aerial, green, ascending organ of the plant developed from Plumule part of an embryo.
• It is Positively Phototropic in nature.
• It consists of stem, leaves and Flowers.

Anatomy of Dicot Stem. EX:-Tridax stem

Transverse section of Dicot stem shows following Anatomical features:-

1. Epidermis
2. Cortex
3. Stele

1) Epidermis: -

• Epidermis is the outermost, single layer of compactly arranged, tubular cells with cuticle on their outer walls.

• It bears multicellular epidermal hairs.
  2) Cortex: -

• Cortex is present internal to Epidermis.

• The outer zone of Cortex present below the epidermis consists of few layers of Collenchyma cells called “Hypodermis”.

• Inner to Hypodermis is several layers of thin walled parenchyma cells. Its Outer cells contain chlorophyll.

• The innermost layer of the cortex is called Endodermis. It is made up of a single layer of barrel shaped cells with abundant starch and hence, called "Starch sheath".
  3) Stele: - Stele is composed of Pericycle, Vascular bundle, Medullary rays and Pith.

• Pericycle:Pericycle is the outer layer of stele. It is sclerenchymatous in nature. There are more layers of Sclerenchyma opposite to Vascular bundles.

• Vascular bundle:- Several Vascular bundles are arranged in a ring (Eustele). Each Vascular Bundle is Conjoint, Collateral, Open with Endarch xylem.(Conjoint-Xylem and Phloem are in a compact bundle, Collateral- xylem and Phloem lie in same radius, open - Strip of Cambium is present between Xylem and Phloem,Endarch- Protoxylem towards pith and Meta xylem towards Pericycle., Phloem is outer and Xylem is inner in position.
  (Xylem contains Vessels, Tracheids, Parenchyma and Fibers).

• Pith (Medulla):- Centre of the stem is occupied by well developed parenchymatous Pith.

Anatomy of Monocot Stem. EX:-Canna stem

Transverse section of Monocot stem shows following Anatomical features:-

1. Epidermis: -

• Epidermis is the outermost, single layer of compactly arranged, tubular cells with cuticle on their outer walls. Epidermal hairs are absent, and Few Stomata are present.

1. Ground tissue: -

• Ground tissue is present internal to Epidermis. Just below epidermis few layers of Sclerenchyma cells are called "Hypodermis".
• Rest of the ground tissue is Parenchymatous in which vascular bundles are scattered (Atactostele). Endodermis; Pericycle, Medullary rays and Pith are absent.

1. Vascular bundle:-

• Vascular bundles are many scattered in the ground tissue. (Atactostele).
• Peripheral vascular bundles are small closely arranged; Central bundles are larger, less crowded.
• Each Vascular Bundle is Conjoint, Collateral, and Closed with endarch xylem. (Conjoint-Xylem and Phloem are in a compact bundle, Collateral-Xylem and Phloem lie in same radius, Closed - Cambium is absent between Xylem and Phloem, Endarch- Protoxylem towards center and Meta xylem towards Periphery,)
• Phloem is outer and Xylem is inner in position.
• (Xylem contains irregularly arranged Tracheids, Four distinct Vessels arranged in the form of letter 'Y'. 2 smaller vessels towards centre constitute Proto xylem and two bigger vessels present laterally constitute Meta xylem.
• Cavity formed due to breaking of proto xylem forms 'Water containing cavity". Phloem consists of Sieve tubes and companinion cells. There is no Phloem parenchyma.

Differences between Monocot and Dicot Stem

Anatomy of Leaf

Introduction:-

• The leaf is a flat, expanded structure borne on