Metaxylem is towards the centre and protoxylem towards the periphery

Protoxylem is towards the centre and metaxylem towards the periphery

Metaxylem is towards the centre and protoxylem towards the periphery

Protoxylem and metaxylem are arranged radially as separate tissues

Protoxylem and metaxylem are on the same side

Root, Stem and Leaves

📚

TISSUE SYSTEM

📖

Epidermal tissue system

▢ Definition: Outer covering of plants

▢ Includes:

Epidermis
Stomata
Trichomes / hairs

📝

Epidermis

Root	Stem	Leaves

▢ Definition: Epi = upon; derma = skin → continuous outer layer interrupted by stomata + lenticels

▢ Layering:

Table 1: Epidermis layering

Type	Occurrence / Example
Generally	Single-layered
Multilayered epidermis	Phylloclades of Casuarina; leaves of Nerium + Ficus; hygroscopic roots of epiphytes
Velamen	Multiple epidermis on hygroscopic roots; cells dead

▢ Cuticle:

•
Present on epidermis of stem + leaves
•
Absent in root
•
Protection to epidermis
•
Checks excessive transpiration

▢ Chloroplast:

•
Epidermal cells living
•
Generally no chloroplast
•
Exceptions → shade plants / sciophytes, hydrophytes, some ferns
•
Guard cells contain chloroplast
•
Guard cells living but heteromorphic due to absence of RUBISCO

▢ Special Epidermal Cells / Contents:

Table 1: Special epidermal points

Structure / Content	Occurrence	Function / Note
Bulliform / motor / bubble-like cells	Upper epidermis of isobilateral leaves / monocots	Rolling + unrolling of leaves; mainly rolling
Epiblema / piliferous layer / rhizodermis	Outermost layer of root	Not cutinised/suberised; no stomata
Stomata + lenticels	Epidermis	Confined to epidermis
Silica	Epidermal cells of grasses + Equisetum	Mechanical strength
Lithocysts	Epidermal cells containing cystoliths	Cystolith = \(CaCO_3\)

📝

Stomata

▢ Definition: Minute pores on epidermal surface of leaves + some herbaceous stems

▢ Structure:

•
Each stoma guarded by 2 guard cells
•
Guard cells = specialized epidermal cells
•
Subsidiary / accessory cells surround guard cells

▢ Guard Cell Shape:

Table 1: Guard cell shape

Plant group	Guard cell shape
Dicots	Kidney-shaped / bean-shaped
Some monocots e.g., doob grass / Cynodon dactylon, maize	Dumb-bell / barbell-shaped

▢ Distribution:

Table 1: Stomatal distribution

Plant / Leaf type	Stomata distribution
Dicot leaves	Scattered; generally lower epidermis
Monocot leaves	Scattered in rows; both surfaces
Free-floating hydrophytes e.g., lotus, Nymphaea	Upper epidermis
Submerged hydrophytes	Absent / non-functional
Algae + fungi	Totally absent

▢ Leaves Based on Stomata:

Table 1: Leaves by stomatal distribution

Leaf type	Stomata found on	Examples
Epistomatic	Upper surface	Free-floating hydrophytes e.g., lotus, Nymphaea
Hypostomatic	Lower surface	Common dicot leaves
Amphistomatic	Both surfaces	Common monocot leaves

📝

Trichome / Hairs

Table 1: Trichomes

Type	Occurrence	Function
Unicellular	Roots	Absorption / protection
Multicellular	Stems	Checks excess water loss + protection

📖

Ground tissue system

▢ Definition: Tissue system between epidermis and vascular tissue

▢ Components:

Hypodermis
Cortex
Endodermis
Pericycle
Medulla / pith
Medullary rays / pith rays
Conjunctive tissue

📝

Hypodermis

Table 1: Hypodermis

Point	Data
Position	Outermost layer of cortex
Herbaceous dicot stem	Collenchymatous
Monocot stem	Sclerenchymatous

📝

Cortex

•
Present inside hypodermis
•
Usually parenchymatous
•
Abundant intercellular space
•
Innermost layer → endodermis

📝

Endodermis / Starch Sheath

▢ Definition: Single-layered tissue separating cortex from stele

▢ System: Part of extrastelar ground tissue system

▢ Cell Features:

•
Barrel-shaped
•
No intercellular spaces
•
Living
•
Starch-containing → starch sheath

▢ Casparian Strips:

•
Radial + tangential wall thickening; mainly radial wall
•
Made of lignin + suberin + cutin
•
Stripes/bands → Casparian strips / Casparian bands
•
Casparian strips + passage cells also found in exodermis

▢ Passage Cells:

•
Present just against protoxylem in root
•
Exodermis may occur in some roots e.g., hygroscopic roots of epiphytes

▢ Root Point: Well-developed endodermis = constant feature of roots; not constant in stem

📝

Pericycle

▢ Position: Inside endodermis

▢ Layers: Single-layered or few-layered

▢ Cell Type: Thin-walled parenchymatous or rarely thick-walled sclerenchymatous

▢ Occurrence:

•
Present in most roots
•
Absent in roots of parasitic plants + hydrophytes

▢ Special Cases:

Table 1: Pericycle special cases

Plant / Case	Pericycle feature
Smilax root / monocot	Multilayered + sclerenchymatous
Sunflower stem	Heterogeneous → thick-walled + thin-walled cells

▢ Functions:

Table 1: Pericycle functions

Pericycle type	Function
Thick-walled	Mechanical
Thin-walled	Storage
Dicot root pericycle	Can form cambium

📝

Medulla / Pith and Medullary Rays

▢ Definitions:

Table 1: Pith and pith rays

Term	Meaning
Medulla / pith	Core of plant axis occupied by parenchymatous tissue
Medullary rays / pith rays	Pith radiating between vascular bundles

▢ Functions:

Table 1: Functions

Structure	Function
Pith	Food storage
Medullary rays	Lateral transportation

▢ Distribution:

Table 1: Pith distribution

Plant part	Pith status
Dicot stem	Distinct / developed
Monocot root	Distinct / developed
Monocot stem	Scattered
Dicot root	Indistinct / small / absent
Triticum stem	Central region hollow → pith cavity
Ricinus	Pith cavity among dicots

📝

Conjunctive Tissue

Parenchymatous tissue between xylem and phloem bundles

📝

Cortex and Stele

Table 1: Cortex vs stele

Region	Meaning
Cortex	Ground tissue outside endodermis
Stele	All tissues inside endodermis
Monocot stele	Atactostele
Dicot stele	Eustele

Endodermis absent in monocot stem → ground tissue not differentiated into cortex and stele

📝

MCQ Point

Q1.

Undifferentiated ground tissue is met within

📖

Vascular tissue system

▢ Definition:

•
Central column of root/stem axis = stele
•
Stele made of vascular bundles
•
Stelar region includes all tissues inside pericycle
•
Vascular bundle = xylem + phloem + cambium if present
•
Cambium = strip of primary meristem

▢ Types of Vascular Bundles:

❖ Radial:

•
Xylem + phloem in separate bundles
•
Present on different radii
•
Alternate arrangement
•
Equal in number
•
Example → roots of dicots + monocots

❖ Conjoint:

▢ Definition: Xylem + phloem in same bundle and same radius

▢ Example: Stem

▢ Types:

❖ Collateral:

Table 1: Collateral vascular bundle

Type	Cambium	Example / Note
Open collateral	Present between xylem + phloem	Dicot stem; conjoint, collateral, open
Closed collateral	Absent	Monocot stem; conjoint, collateral, closed

Phloem outside/pericycle side; xylem towards centre/pith

❖ Bicollateral:

▢ Definition: Phloem present on both sides of xylem

▢ Bundle Nature: Always open

▢ Arrangement: Phloem → cambium → xylem → cambium → phloem

▢ Examples:

•
Stem of Cucurbitaceae
•
Stem of Solanaceae
•
Stem of Convolvulaceae

▢ MCQ Point:

Q1.

Bicollateral vascular bundles are found in the stem of

❖ Concentric:

▢ Definition: Xylem + phloem arranged in definite circle

▢ Nature: Always closed

▢ Occurrence: Characteristic of pteridophytes + few monocots

▢ Types:

Table 1: Concentric vascular bundles

Type	Arrangement	Examples
Amphicribal / hadrocentric	Xylem central; phloem surrounds xylem	Ferns, some aquatic angiosperms, Lycopodium, Selaginella
Amphivasal / leptocentric	Phloem central; xylem surrounds phloem	Underground stem of some monocots e.g., dagger plant / Yucca, dragon plant / Dracaena, sweet flag / Acorus

📚

ROOT-STEM TRANSITION

•
Conversion: radial + exarch vascular bundle → conjoint + endarch vascular bundle
•
Xylem swings during transition
•
Phloem remains stationary
•
Transition zone present in hypocotyl

📚

ORIGIN OF LATERAL ROOTS AND LATERAL BRANCHES OF STEM

Table 1: Origin of lateral organs

Structure	Origin	Source / Seat
Lateral root	Endogenous	Pericycle
Seat of lateral root origin	Just against protoxylem	Pericycle opposite protoxylem
Lateral branch of stem	Exogenous	Outer part of cortex

📚

ANATOMY OF STEM

▢ Dicot Stem vs Monocot Stem:

Table 1: Anatomy of dicot and monocot stem

Feature	Dicot stem	Monocot stem

Epidermis	Epidermis with multicellular hairs + stomata with kidney-shaped guard cells	Outer epidermis cutinized; stomata with dumb-bell-shaped guard cells
Hypodermis	Collenchymatous	Sclerenchymatous
Internal tissue arrangement	Concentric	Concentric arrangement absent
Ground tissue	Differentiated into hypodermis, general cortex, endodermis, pericycle, pith	Not differentiated
Stem centre	Almost always solid	Usually hollow centre; exception maize
Vascular bundle arrangement	Ring around pith	Scattered throughout ground tissue
Vascular bundle number/size	Few + similar size	Numerous; smaller at periphery, larger towards central axis
Vascular bundle type	Conjoint, collateral, open	Conjoint, collateral, closed
Bundle sheath	Absent	Sclerenchymatous bundle sheath present
Bundle outline	Wedge-shaped	Oval / rounded
Phloem parenchyma	Present	Absent
Protoxylem cavity	Absent	Present; exception Asparagus
Vessel arrangement	Rows/chains; linear fashion	Y-shaped manner
Stele	Eustele / dictyostele	Atactostele; most advanced stele
Pericycle	Alternating zones of parenchyma + sclerenchyma	Mostly absent
Medullary rays	Present	Absent
Secondary growth	Present	Absent

📚

ANATOMY OF ROOT

▢ Common Features of Dicot and Monocot Roots:

•
Wide cortex made of thin-walled cells
•
Vascular bundle radial
•
Xylem exarch
•
Distinct endodermis + passage cells
•
Lateral roots arise opposite protoxylem points from pericycle → endogenous

▢ Dicot Root vs Monocot Root:

Table 1: Anatomy of dicot and monocot root

Feature	Dicot root	Monocot root

Cortex	Narrow	Very wide
Outer tissues during secondary growth	Epiblema, cortex, endodermis peeled off and replaced by cork	Cork not formed; only epiblema peeled off; cortex + endodermis persist
Endodermis	Less thickened; Casparian strips prominent	Casparian strips visible only in young roots; later endodermal cells highly thickened
Passage cells	Generally absent	Generally present in endodermis opposite protoxylem
Pericycle produces	Lateral roots + cork cambium + vascular cambium	Lateral roots only
Xylem and phloem bundles	Diarch to hexarch / \(2-6\)	Polyarch / \(>8\)
Conjunctive tissue	Parenchymatous	Parenchymatous or sclerenchymatous
Conjunctive parenchyma	Forms cambium	Does not form cambium
Pith	Small or absent	Well-developed
Protoxylem and metaxylem	Linear fashion	Linear or V-shaped
Secondary growth	Present	Absent

▢ Special Points:

•
Grafting not possible in monocots → cambium absent
•
Girdling not possible due to scattered vascular bundles

📚

HISTOLOGY OF LEAF

▢ General Points:

•
Dicot leaf horizontal; upper sun-facing part darker → dorsiventral leaf
•
Monocot leaf nearly vertical; both surfaces equally exposed → isobilateral leaf
•
Leaf anatomy → upper epidermis + lower epidermis + mesophyll + vascular bundle
•
Inverted vascular bundle → xylem upper side, phloem lower side

▢ Vascular Bundle:

•
Conjoint
•
Collateral
•
Mesarch xylem

▢ Dicot Leaf vs Monocot Leaf:

Table 1: Histology of dicot and monocot leaf

Feature	Dicot leaf	Monocot leaf

Cuticle thickness	Upper epidermis thicker than lower epidermis	Same in both epidermis
Bulliform / motor cells	Absent	Present
Number of stomata	Greater on lower surface than upper	Equal on both surfaces
Guard cells	Kidney-shaped	Dumb-bell-shaped
Mesophyll	Differentiated into upper tightly packed palisade parenchyma + lower loosely arranged spongy parenchyma	Not differentiated into palisade and spongy parenchyma
Bundle sheath extension	Present in larger veins; parenchymatous	Present; sclerenchymatous
Bundle sheath cells	Colourless
Lysigenous cavity in xylem	Absent	Usually present

Q1.

Bicollateral vascular bundles are present in:

📅CEE MBBS 2025

Q2.

Cucurbit stems characteristically have:

📅CEE MBBS 2024a

Q3.

Conjoint, collateral and open vascular bundles occur in a typical:

📅CEE MBBS 2022

Q4.

Radial vascular bundles are typically found in:

📅CEE MBBS 2022

Q5.

Vascular bundles surrounded by a sclerenchymatous bundle sheath are characteristic of a typical:

📅CEE MBBS 2022

Q6.

Conjoint, bicollateral and open vascular bundles are characteristic of:

📅CEE MBBS 2022

Q7.

Conjoint, collateral and open vascular bundles are found in:

📅CEE MBBS 2021

Q8.

Which tissue system provides the primary covering of a young plant body?

📅CEE BDS 2023

Q9.

Eustele is characteristic of a:

📅CEE BDS 2021

Q10.

Casparian strips are found in the:

📅CEE BDS 2021

Q11.

A vascular bundle with phloem at the centre surrounded by xylem is called:

📅IOM 2004

Q12.

The arrangement of vascular bundles in a typical monocot stem is called:

📅IOM 1998

Q13.

Lateral roots arise from the:

📅IOM 1996

Q14.

The xylem of a typical root is:

📅IOM 1999

Q15.

Grass leaves roll during water stress primarily because of:

📅BPKIHS 2001

Q16.

In exarch xylem:

📅BPKIHS 2001

Q17.

The hypodermis of a typical monocot stem is:

📅MOE 2062

Q18.

Bicollateral vascular bundles occur in:

📅MOE 2060

Q19.

Scattered vascular bundles are characteristic of the stem of:

📅MOE 2003

Q20.

Lateral roots originate from the:

📅MOE 2002

Q21.

A typical maize stem has vascular bundles that are:

📅MOE 2058

Q22.

When metaxylem lies towards the pith and protoxylem towards the periphery, the xylem is:

📅MOE 2059

Q23.

The xylem arrangement in a typical dicot stem is:

📅MOE 2055

Q24.

A well-developed pith is generally found in:

📅BPKIHS 1994

Q25.

The photosynthetic mesophyll of a typical green leaf is composed mainly of:

📅BPKIHS 1997

Q26.

Atactostele is characteristic of:

📅BPKIHS 1998

Q27.

A vascular bundle with phloem on both the outer and inner sides of xylem is:

📅IOM 2007

Q28.

The hypodermis of a typical monocot stem is:

📅IE 2003

Q29.

Casparian strips are present in the:

📅IE 2004

Q30.

Both palisade and spongy mesophyll cells function mainly to:

📅IE 2007

Q31.

The pericycle that initiates lateral roots contains cells that become:

📅IE 2009

Q32.

In a dorsiventral dicot leaf, the protoxylem and most stomata occur, respectively, on the:

📅I.E.

Q33.

A collateral vascular bundle may be:

📅BPKIHS 2014

Q34.

Vascular bundles in a typical dicot stem are:

📅MOE 2014

Q35.

Casparian strips occur in the:

📅MOE 2010

12Root, Stem and Leaves

Table 1: Epidermis layering

Table 1: Special epidermal points

Table 1: Guard cell shape

Table 1: Stomatal distribution

Table 1: Leaves by stomatal distribution

Table 1: Trichomes

Table 1: Hypodermis

Table 1: Pericycle special cases

Table 1: Pericycle functions

Table 1: Pith and pith rays

Table 1: Functions

Table 1: Pith distribution

Table 1: Cortex vs stele

Table 1: Collateral vascular bundle

Table 1: Concentric vascular bundles

Table 1: Origin of lateral organs

Table 1: Anatomy of dicot and monocot stem

Table 1: Anatomy of dicot and monocot root

Table 1: Histology of dicot and monocot leaf

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