Anatomy of Flowering Plants – Complete Notes

Contents Anatomy and Tissue — Introduction Meristematic Tissue Simple Permanent Tissue Sclerenchyma — Fibres and Sclereids Complex Permanent Tissue — Xylem and Phloem Tissue System T.S. of Dicot Root T.S. of Monocot Root T.S. of Dicot Stem T.S. of Monocot Stem L.S. of Dicot and Monocot Leaf Secondary Growth Practice Questions Download Notes

Anatomy — Introduction

Anatomy (Anatome) is the study of internal tissues of a plant.

Tissue: A group of cells having common origin and working together with a common function.

Classification of Tissue

Meristematic Tissue — actively dividing cells responsible for growth.
Permanent Tissue — cells stop dividing.
- Simple Permanent Tissue (made up of only one type of cell): Parenchyma, Collenchyma, Sclerenchyma
- Complex Permanent Tissue (more than one type of cell): Xylem, Phloem

Meristematic Tissue

Meristem is the location where cell division (Meristematic activity) occurs.

Features of Meristematic Cells

Small size cells.
Dense cytoplasm.
Round or oval shape.
Thin cell wall.
Vacuole — absent or very small.

Apical Meristem and Primary Tissues

Root Apical Meristem (Primary): Located at the root tip. Gives rise to three primary meristems:
Protoderm — forms Epidermis
Ground Meristem — gives Cortex
Procambium — gives Vascular cylinder/bundle (Primary xylem and phloem)

The root apical meristem also forms the Root Cap, which is absent in the shoot apex.

Shoot Apical Meristem: Located at the distal-most part of the shoot. It has an undifferentiated, dome-shaped structure, with leaf primordia developing laterally and axillary buds left behind.

Types of Meristem (On the Basis of Position)

Type	Location / Description
Apical Meristem	At the tip of root and shoot.
Intercalary Meristem (in Monocot)	Present at the base of internodes — helps regenerate the apical part when grazed/eaten, and increases internode length.
Lateral Meristem	Present on the sides of root/stem. e.g. Vascular cambium, Cork cambium — Secondary meristems, involved in increase of girth (secondary growth).

Classification of Meristem — On the Basis of Origin

(a) Primary Meristem: Develops directly from the embryo, present in the primary organs (Root, Stem, Leaf). e.g. Apical meristem, Intercalary meristem.

(b) Secondary Meristem: Result of redifferentiation, derived from permanent tissue. e.g. Vascular cambium, Cork cambium (Phellogen).

Classification of Meristem — On the Basis of Fate

Meristem	Gives Rise To
Protoderm	Epidermis
Ground Meristem	Cortex
Procambium	Primary Xylem and Primary Phloem (vascular tissue)
Vascular Cambium (Secondary meristem)	Secondary Xylem and Secondary Phloem
Cork Cambium / Phellogen (Secondary meristem)	Cork (Phellem) and Secondary Cortex (Phelloderm)

Differentiation, Dedifferentiation, Redifferentiation

Differentiation: Meristematic cells undergo changes to form permanent tissue, and lose the capacity to divide.

Dedifferentiation: Permanent tissue cells regain the capacity to divide (e.g. cortex/pericycle cells become interfascicular cambium, or cork cambium).

Redifferentiation: Cells produced by dedifferentiation again differentiate and lose the capacity to divide, forming new permanent tissue (e.g. secondary xylem, secondary phloem, cork).

List of Primary and Secondary Tissue

Tissue	Primary / Secondary
Epidermis	Primary
Cortex	Primary
Primary Xylem	Primary
Primary Phloem	Primary
Secondary Xylem	Secondary
Secondary Phloem	Secondary
Cork (Phellum)	Secondary
Secondary Cortex	Secondary

Form-wise: Leaf — Primary organ. Stem — Primary organ. Root — Primary organ. Cork — Secondary tissue.

Simple Permanent Tissue

Permanent tissue means cells that stop dividing. Simple permanent tissue is made up of only one type of cell.

(1) Parenchyma Tissue

Shape: Isodiametric (oval, round, polygonal, spherical).

Cell wall: Thin, made of cellulose. Intercellular space present.

Functions:
Photosynthesis: In leaf mesophyll — Palisade Parenchyma and Spongy Parenchyma.
Storage: Storage parenchyma.
Aerenchyma: Parenchyma with air cavities/space — present in roots of aquatic plants (Hydrophytes) and some monocots, provides buoyancy.

Only Parenchyma has chloroplast (when present, called Chlorenchyma) — no other simple permanent tissue (Collenchyma, Sclerenchyma) has chloroplast typically.

(2) Collenchyma Tissue

Shape: Oval, Spherical, Polygonal.

Cell wall deposition: Hemicellulose, Pectin and Lignin (carbohydrate-based components) deposited unevenly — not uniform, deposited at corners.

Intercellular space: Absent (cells compactly arranged).

Function: Mechanical role; can be photosynthetic (have chloroplast).

Location: Petiole, Green Dicot stem (as homolayer/complete layer in hypodermis) — absent in Root and Monocot.

Sclerenchyma Tissue

Shape: Elongated, Polygonal, Pitted.

Cell wall deposition: Lignin.

Intercellular space: Absent.

Nature: Dead cell, devoid of protoplasm (lumen obliterated due to lignin deposition).

Pit: A region where lignin is NOT deposited (gap in the lignified wall). Pit Membrane = Middle Lamella + Primary Cell Wall.

Pits — Note

Vessels, Tracheids, and Fibres — all three have pits. In Tracheids, transport of water occurs through pits. Pit membrane includes primary cell wall and middle lamella, with the plasma membrane lining the cell.

Types of Sclereids (Based on Structure/Origin/Development)

Type	Shape	Location
Brachysclereid	Short / cuboid	Pulp of pear, Guava (gritty/stone cells)
Macrosclereid	Elongated, rod-shaped	Epidermis of legume seed
Osteosclereid	Bone-shaped (dumbbell)	Sub-epidermis of legume seed
Astrosclereid	Star-shaped	Leaf of Tea

Fibres — Location

Type	Location
Xylem Fibre	Within xylem (in xylem bundle)
Phloem Fibre	Within phloem; in hypodermis of Arecaceae (Palm family)

Complex Permanent Tissue

Xylem (Hadrome)

Xylem transports water and minerals. Xylem tissue develops in Root, Stem, Leaf, and has four types of cells:

Component	Living / Dead	Function / Feature
Tracheids	Dead	Conducts water through pits
Vessels (Vessel elements)	Dead	End-to-end transport, perforated end walls
Xylem Fibre	Dead	Lignified, pitted, obliterated lumen; mechanical support
Xylem Parenchyma	Living	Storage — oil, starch, tannin

Vessels — Types (Based on Lignin Pattern)

Spiral, Reticulate, Annular, Scalariform, Pitted (these patterns describe lignin deposition on vessel walls). Septate vessels — found only in Metaxylem; end walls contain large pits.

Difference: Vessels vs Tracheids

Feature	Vessel	Tracheid
Structure	Multi-membered (many cells joined end to end)	Single elongated, tapering cell
Perforation	Present — end-to-end transport	Absent — transport through pit pairs
Wall thickness	Thinner than tracheid	Thicker than vessel
Lumen	Wider	Narrower

Similarity Between Vessels and Tracheids

Both are lignified, pitted, dead, and enucleated.
Both provide mechanical support.
Both are part of the Apoplast pathway for water transport.

Note: Gymnosperms lack vessels except Gnetum and Ephedra (Welwitschia — connecting link). All Angiosperms have vessels except some primitive families (e.g. Winteraceae, Tetracentraceae). A plant having vessels has a "porous wood".

Types of Xylem — Primary and Secondary

Primary Xylem: Develops from primary meristem (procambium) — has Protoxylem (first formed) and Metaxylem (later formed).

Secondary Xylem: Develops from vascular cambium.

Arrangement of Protoxylem and Metaxylem — Exarch and Endarch

Type	Arrangement	Found In
Exarch	Protoxylem towards periphery (outer), Metaxylem towards centre (inner) — centripetal development	Root
Endarch	Protoxylem (inner), Metaxylem (outer) — centrifugal development	Stem

Phloem (Leptome)

Phloem bundle has four types of cells:

Component	Living / Dead	Feature
Sieve Tube	Living (enucleate at maturity)	Made up of many sieve elements with sieve plates
Companion Cell	Living, Nucleated	Associated with sieve tube via plasmodesmatal connections
Phloem Parenchyma	Living	Elongated, dense cytoplasm — storage of resin, mucilage, gums. Absent in Monocots.
Phloem Fibre / Bast Fibre	Dead	Elongated, lignified; used as commercial fibre (e.g. Jute, Hemp). Present in secondary phloem (dicots).

Sieve Tube — Structure

Sieve tube is made up of many sieve elements. On the transverse (end) wall, a Sieve Plate is present containing Sieve pores, through which sieve elements are connected (plasmodesmatal connections). The sieve tube has a large vacuole, peripheral cytoplasm, and lacks a nucleus at maturity — its functions are maintained by the adjacent Companion Cell.

P-Protein (Phloem Protein): Present in sieve tubes — function: protects from injury and helps maintain pressure gradient (also called slime plugs).

Phloem — Presence/Absence in Different Organs

Organ	Phloem Parenchyma	Phloem Fibre
Dicot Stem	Present	Present (secondary phloem)
Dicot Root	Present	Present
Monocot Stem	Absent	Absent
Monocot Root	Absent	Absent
Monocot Leaf	Absent	Absent

Type of Phloem

(A) Primary Phloem: Formed by primary meristem (procambium) via differentiation — has Protophloem and Metaphloem.

(B) Secondary Phloem: Product of redifferentiation by vascular cambium.

Tissue System

In a transverse section of root/stem, there are three types of Tissue Systems:

(1) Epidermal Tissue System — outermost layer.

(2) Ground Tissue System — Cortex, Pith, Medullary ray, Pericycle.

(3) Vascular Tissue System — Xylem and Phloem.

Epidermal Tissue

Made of Parenchyma cells, elongated, with no chloroplast (except in guard cells of stomata).
No intercellular space, vacuole present.
Role: Protection.
Made of a single layer of epidermis + appendages.

Epidermal Appendages

Appendage	Type of Cell	Location / Feature
Root Hair (Epiblema)	Unicellular, Unbranched outgrowth	Root — for Absorption (water and minerals)
Trichome	Multicellular outgrowth (branched or unbranched)	Leaf and stem — can secrete crystals, prevent transpiration
Cuticle	Waxy layer	Leaf — prevents water loss/transpiration
Stomata	Guard cells + stomatal pore + subsidiary cells	Leaf — gas exchange
Lenticels	Complementary cells	Stem (bark) — gas exchange in older stems

Stomata Structure

Stomata consist of a Stomatal Pore surrounded by two Guard Cells (with radially arranged cellulose microfibrils — inner wall thick/elastic, outer wall thin), and surrounded by Subsidiary Cells.

Vascular Bundle Arrangement Types

Type	Description	Example
Radial	Xylem and Phloem on different radii	Dicot Root, Monocot Root
Conjoint — Collateral, Open	Xylem and Phloem on the same radius (outer phloem, inner xylem); cambium present	Dicot Stem
Conjoint — Collateral, Closed	Same as above, but cambium absent	Monocot Stem, Dicot Leaf, Monocot Leaf
Concentric (Amphivasal/Amphicribal)	One tissue surrounds the other	Some monocot rhizomes, ferns

T.S. of Dicot Root

Epidermis: Elongated parenchyma cells, intercellular space present, root hair present.
Cortex: Small sized, round parenchyma cells, intercellular space present.
Endodermis: Barrel-shaped cells, innermost layer of cortex. Radial walls have Casparian strips (made of suberin, in form of bands/casparian thickening).
Pericycle: Made of parenchyma. Undergoes dedifferentiation to produce lateral roots; also forms vascular cambium and cork cambium during secondary growth.
Conjunctive Tissue: Present between Xylem and Phloem (parenchyma).
Pith: Parenchyma cells — small (or absent) in dicot root.

Stele — Definition

Stele = Pericycle + Vascular Bundle + Conjunctive Tissue + Pith. Pith is part of both Ground Tissue and Stele. Tissue that is "ground tissue but not stele" = Cortex. Tissue that is "stele but not ground tissue" = Vascular Bundle.

Vascular Bundle of Dicot Root

Radial arrangement. Exarch xylem (Protoxylem outer, Metaxylem inner). Number of xylem strands: usually Diarch to Hexarch (2 to 6 — i.e. limited number).

Note — Tissue Composition (Dicot Root)

Tissue	Cell Type
Cortex	Parenchyma [P]
Endodermis	Parenchyma [P] (with casparian strips)
Pith / Medulla	Parenchyma [P] (or absent)

T.S. of Monocot Root

Similar to dicot root, except:

Vascular bundle is Polyarch (more than 6 xylem strands).
Pith is large/conspicuous.
Pericycle does not undergo dedifferentiation — no secondary growth occurs (no lateral root formation in the typical dicot sense via pericycle, and no vascular cambium forms).

Comparison: Monocot Root vs Dicot Root

Feature	Monocot Root	Dicot Root
Xylem arrangement	Polyarch	Diarch to Hexarch
Pith	Large	Small (or absent)
Secondary growth	No secondary growth occurs	Occurs

T.S. of Dicot Stem

Layers from outside to inside:

Layer	Cell Type / Description
Epidermis	Has cuticle, few stomata and trichomes
Hypodermis	Collenchyma [C] (outer cortex region)
Cortical cells (general cortex)	Parenchyma [P]
Endodermis (Starch sheath)	Parenchyma [P] — contains stored starch, called Starch Sheath
Pericycle	Sclerenchyma [S] — present as a semilunar patch above each vascular bundle
Medullary Rays	Made of parenchyma, involved in radial conduction; can undergo dedifferentiation to form interfascicular cambium
Pith	Parenchyma — large pith present

Vascular Bundle of Dicot Stem

Wedge-shaped (triangular), present in the form of a ring (Eustele). It is Conjoint, Collateral, Open (cambium present between xylem and phloem). Vascular bundles are equal in size.

T.S. of Monocot Stem

Epidermis made of Parenchyma; Hypodermis made of Sclerenchyma.
Cortex, Pith, Pericycle, Endodermis are not distinctly demarcated as separate layers — Ground tissue is largely undifferentiated.
Vascular bundles are scattered — this arrangement is called Atactostele.
Vascular bundles of unequal size — larger ones towards the inner region, smaller ones towards the periphery.
Vascular bundle type: Conjoint, Collateral, Closed (no cambium).
Protoxylem elements often disintegrate, forming a water-filled cavity called the Protoxylem lacuna (water cavity).

Comparison: Dicot Stem vs Monocot Stem

Feature	Dicot Stem	Monocot Stem
Hypodermis	Collenchyma	Sclerenchyma
Pith, Endodermis, Pericycle	Present/distinct	Absent / not distinct (ground tissue undifferentiated)
Vascular bundle shape	Triangular	Circular/oval, scattered
Vascular bundle size	Equal size, arranged in a ring (Eustele)	Unequal size, scattered (Atactostele)
Vascular bundle type	Conjoint, Collateral, Open	Conjoint, Collateral, Closed

L.S. of Dicot and Monocot Leaf

Dicot Leaf (Dorsiventral Leaf)

Adaxial surface (upper): Has Palisade cells (column-shaped, closely packed — main photosynthetic region).
Abaxial surface (lower): Has Spongy Parenchyma (loosely arranged, with air spaces).
Stomata: Present mainly on the lower (abaxial) surface.
Vascular bundle: Conjoint, Collateral, Closed; unequal size as per the size of vein.

Monocot Leaf (Isobilateral Leaf)

Stomata: Present on both surfaces (upper and lower).
Mesophyll cells present, with no distinction between palisade and spongy parenchyma (isobilateral — both layers similar).
Vascular bundles are nearly equal in size, except the mid-vein vascular bundle (which is larger).
Bulliform cells: Present on the adaxial surface — large, colourless, non-photosynthetic cells that help in keeping the leaf in an extended/unrolled form (involved in leaf rolling/unrolling during water stress).
Each vascular bundle is surrounded by a Bundle Sheath of cells.

Secondary Growth

Secondary growth occurs in that part of the plant where primary growth has been completed, with the help of secondary meristems. Secondary growth occurs in Dicot root and Dicot stem. Monocots lack secondary growth.

Secondary Meristems

Vascular Cambium = Intrafascicular Cambium (between primary xylem and primary phloem, present from the start — a primary meristem remnant) + Interfascicular Cambium (formed from medullary ray cells — secondary meristem, derived via dedifferentiation). Together they form a complete ring (unilayer) of vascular cambium.

Cork Cambium (Phellogen): Derived from cortex (few layers); also called secondary cortex producer. A few plants like Yucca derive cork cambium from epidermis to endodermis layers (in root and stem).

Activity of Vascular Cambium

Vascular cambium divides to form Secondary Xylem (towards inside) and Secondary Phloem (towards outside). The vascular cambium is more active towards the inside, producing more secondary xylem than secondary phloem. Due to this, the cambium ring gradually shifts outward, and the primary phloem and early secondary phloem get crushed/non-functional.

Spring Wood and Autumn Wood

Spring Wood (Early wood): Formed when vascular cambium is more active — produces secondary xylem with wide lumen vessels and more bundle sheath cells; appears lighter in colour.

Autumn Wood (Late wood): Formed when vascular cambium is less active — produces secondary xylem with narrow lumen vessels and fewer bundle sheath cells; appears darker.

The alternating light (spring) and dark (autumn) bands form Annual Rings (Growth Rings) — used for age determination (dendrochronology). In tropical conditions and near the coast (where seasons are less distinct), annual rings may be absent or less visible.

Sap Wood and Heart Wood

Sap Wood (Outer): Living, peripheral region of secondary xylem — conducting xylem (transports water from root to leaves).

Heart Wood (Inner): Dead, many layers, non-conducting. Vessels and tracheids get blocked. In thick/old stems, inner secondary xylem becomes dead — Xylem parenchyma deposits tannin, lignin, gum and other microbially-resistant substances inside xylem vessels, giving heartwood its dark colour and resistance.

Activity of Cork Cambium and Bark Formation

Cork cambium is active alongside vascular cambium. Cork cambium divides periclinally (parallel to the surface) to produce Phellum (Cork) on the outside — dead cells due to deposition of Suberin.

Periderm = Phellum (Cork) + Phellogen (Cork Cambium) + Phelloderm (Secondary Cortex).

Bark: All tissues external to the vascular cambium are collectively called Bark.
Early Bark (Soft bark): Tissue formed in spring.
Late/Hard Bark: Tissue formed in autumn.

Layers in Bark (Outside to Inside)

Cork (Phellum) → Cork Cambium (Phellogen) → Secondary Cortex (Phelloderm) → Cortex → Endodermis → Pericycle → Primary Phloem → Secondary Phloem → Vascular Cambium (innermost of "bark" region, separating bark from wood).

Lenticels

Lenticels are lens-shaped openings on the stem (bark) for gaseous exchange — formed due to the activity of cork cambium producing loosely arranged complementary cells (rather than compact cork cells) at certain points on the epidermis/periderm.

Secondary Growth in Roots

Secondary growth in roots is similar to that in stems. Vascular cambium forms (from conjunctive tissue between xylem and phloem, plus pericycle contribution), and produces secondary xylem and secondary phloem, eventually forming a continuous ring, similar to the stem.

Practice Questions

Q1. The Root Apical Meristem gives rise to which structure that is absent in the Shoot Apical Meristem?

(a) Protoderm (b) Root Cap (c) Procambium (d) Ground Meristem

Answer: (b) Root Cap

Explanation: Both root and shoot apical meristems give rise to the three primary meristems — Protoderm (forms epidermis), Ground meristem (forms cortex), and Procambium (forms vascular tissue). However, only the Root Apical Meristem additionally produces the Root Cap, a protective structure covering the root tip, which has no equivalent at the shoot apex.

Q2. Which tissue is responsible for buoyancy in aquatic plants due to the presence of large air spaces?

(a) Collenchyma (b) Sclerenchyma (c) Aerenchyma (d) Phloem parenchyma

Answer: (c) Aerenchyma

Explanation: Aerenchyma is a type of parenchyma with large air cavities/spaces between cells, commonly found in roots of aquatic plants (hydrophytes) and some monocots. These air spaces help the plant float (buoyancy) and also facilitate internal gas exchange. Collenchyma provides mechanical support with uneven wall thickening, while sclerenchyma provides rigidity with lignified dead cells.

Q3. The casparian strips, made of suberin, are found in which layer of the dicot root?

(a) Epidermis (b) Cortex (c) Endodermis (d) Pericycle

Answer: (c) Endodermis

Explanation: The Endodermis is the innermost layer of the cortex in the dicot root, made up of barrel-shaped cells. Their radial walls contain casparian strips/bands made of suberin, which form a waterproof barrier. This forces water and minerals moving through the apoplast pathway to cross the plasma membrane (symplast pathway) at this point, allowing selective uptake of substances into the vascular cylinder.

Q4. The vascular bundles in a dicot stem are arranged as Conjoint, Collateral and Open. What does "Open" signify here?

(a) The vascular bundle is scattered throughout the stem

(b) Cambium is present between the xylem and phloem

(d) The bundle sheath is absent

Answer: (b) Cambium is present between the xylem and phloem

Explanation: In a "Conjoint" vascular bundle, xylem and phloem are part of the same bundle. "Collateral" means xylem and phloem are arranged side-by-side on the same radius (typically phloem outer, xylem inner). "Open" specifically refers to the presence of cambium between the xylem and phloem, which allows for secondary growth — this is characteristic of dicot stems, unlike monocot stems/leaves which are "closed" (cambium absent).

Q5. Which of the following best explains the formation of annual (growth) rings in the secondary xylem of a tree?

(a) Alternating activity of cork cambium in summer and winter

(b) Alternating bands of spring wood (wide lumen, more active cambium) and autumn wood (narrow lumen, less active cambium)

(d) Periodic formation of lenticels on the bark

Answer: (b) Alternating bands of spring wood (wide lumen, more active cambium) and autumn wood (narrow lumen, less active cambium)

Explanation: Annual rings are formed due to seasonal variation in the activity of the vascular cambium. In favourable seasons (spring), the cambium is highly active, producing secondary xylem with vessels of wide lumen and more bundle sheath cells, appearing lighter (spring wood/early wood). In less favourable seasons (autumn), the cambium is less active, producing xylem with narrow lumen and fewer bundle sheath cells, appearing darker (autumn wood/late wood). This alternating light-dark pattern forms a visible annual ring, and is typically absent or unclear in tropical regions with less distinct seasons.

Q6. Bulliform cells, which help keep the leaf in an extended form, are found in:

(a) Adaxial surface of dicot leaf (b) Abaxial surface of dicot leaf (c) Adaxial surface of monocot (isobilateral) leaf (d) Phloem of monocot leaf

Answer: (c) Adaxial surface of monocot (isobilateral) leaf

Explanation: Bulliform cells are large, colourless, non-photosynthetic cells present on the adaxial (upper) surface of monocot (isobilateral) leaves. They help in keeping the leaf in an extended/unrolled form and are involved in leaf rolling/folding responses (e.g. during water stress, helping to reduce water loss). Dicot (dorsiventral) leaves do not have bulliform cells — they instead show a clear distinction between palisade (adaxial) and spongy (abaxial) parenchyma.

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