SHAHINA AKTHERGRADE 11

GULF ASIAN ENGLISH SCHOOL

ANATOMY OF FLOWERING PLANTS

Anatomy

Study of internal organisation of living organisms

Histology

Study of tissues & tissue system in multicellular organisms

1. TISSUE

• Group of cells, having common origin

Tissues

Meristematic Tissue

Permanent Tissues

Simple Permanent Tissues1) Parenchyma2) Collenchyma3) Sclerenchyma

Complex Permanent Tissues1) Xylem2) Phloem

2. MERISTEMATIC TISSUES

• Cells have power of division• A. Characteristics of Meristematic Tissues Cells are thin walled Have abundant cytoplasm Retain power of division No intracellular spaces

B. Classification of meristems :

• Based on position in plant body• (i) Apical meristems• Occur at apices• Differentiate into primary tissues• Cause increase in length• Axillary buds are present in axils of leaves

(ii) Lateral meristems :

Arranged parallel to the sides of organs of plant

Cells produced by them differentiate into secondary tissues

Cause increase in width of plant organ

e.g., Fascicular cambium & cork cambium

(iii) Intercalary meristems :

Meristems occur in between mature/permanenet tissues

Produce cells that form primary tissues

Cause increase in length

Occur at bases of internodes & leaf sheaths of grasses & other monocots;They regenerate parts removed by grazing animals

Based on origin

(i) Promeristems :

Group of meristematic cells in embryo / seedlings

Give rise to primary meristems

(ii) Primary meristems :

Formed from promeristems

Cells produced by them differentiate into primary / secondary permanent tissues

e.g., Apical meristems, fascicular cambium & intercalary meristem

(iii) Secondary meristems :

Formed at a later stage in the life of plant from permanent tissues by process of dedifferentiation, e.g., Cork cambium & inter-fascicular cambium

3. PERMANENT TISSUES

• Cells have lost power of division & become structurally & functionally specialised

Characteristics :

Cells have lost power of division

Undergone differentiation into specific types for a particular function

2 types:

(i) Simple permanent tissues ( Tissue composed of 1 type of cell)(ii) Complex permanent tissues ( Tissue is composed of more than 1

type of cell)

B. Simple Permanent Tissues :(i) Parenchyma

Cells are thin- walled

Isodiametric

Retain capacity to divide at maturity

No intracellular spaces

Main function is storage

When parenchyma cells contain a number of chloroplasts they are called chlorenchyma & when they are arranged with regular system of intercellular air spaces, they constitute aerenchyma

Forms major component of any organ of plant

(ii) Collenchyma

Cells living at maturity

Cells are variously shaped

Cell wall is unevenly thickened

Occurs below epidermis of dicot stem

Cells may possess chloroplast

Provides strength & flexibility to growing organs

(iii) Sclerenchyma Cells are dead at maturity

Cell wall is lignified evenly

Gives mechanical support to organs

Has 2 types of cells :

(a) SCLEREIDS (STONE CELLS) :

Oval/spherical & have very thick walls with narrow lumen

Occur in shells of nuts & in pulp of fruits & in tea leaves

(b) FIBRES :

Elongated & thick walled cells

Generally occur in groups

Present in xylem , phloem & cortex & pericycle

C. Complex Permanent Tissues :(i) XYLEM :

Forms continuous channel

Concerned with transport of water & minerals

Provides mechanical support

Composed of tracheary elements, xylem parenchyma & xylem fibres

(a) XYLEM VESSELS :

Long cylindrical tubular structures formed by many cells

End walls of vessel members have either single large opening / perforation / several small openings

Have thick lignified walls

Vessles are dead at maturity & found in angiosperms only

(b) XYLEM TRACHEIDS :

Elongated cells

Overlap one another at their slanting ends

Do not have perforation plates

Have thick lignified walls

Dead at maturity

(c) XYLEM PARENCHYMA ;

Thick/ thin walls of cellulose Only living components of xylem

Involved in short distance transport

Help in storage of sugars, starch, lipids & tannins

(d) XYLEM FIBRES ( SCLERENCHYMA)Dead elements

Provide mechanical support

Xylem formed in primary plant body by procambium is called primary xylem

1st formed primary xylem is called protoxylem

Later formed is called metaxylem

In stems, protoxylem lies towards pith & metaxylem towards periphery ; such an arrangement is called endarch

In roots, protoxylem lies towards periphery & metaxylem towards pith ; such an arrangement is called exarch

Xylem constituents formed by fascicular cambium constitue secondary xylem

(ii) PHLOEM

• Concerned with transport of organic substances

• Composed of sieve elements, companion cells, phloem parenchyma & phloem fibres

(a) SIEVE TUBES:

Formed by elongated sieve tube members

Cross walls have number of perforations

Mature sieve tube has peripheral cytoplasm

Functions are controlled by nucleus of companion cells

Members are characteristically present in angiosperms

(a) SIEVE CELLS :

Sieve areas are found to occur throughout the end walls & lateral walls

Cells are living, but lack nucleus

Found in lower vascular plants

(c) COMPANION CELLS:

Found in association with sieve tube members

Sieve tube elements & companion cells are connected by pit fields

Help in maintaining the pressure gradient

(d) PHLOEM PARENCHYMA :

Cells are elongated & cylindrical

Have dense cytoplasm & prominent nucleus

Stores food materials & other substances

Absent in monocot plants

(e) PHLOEM FIBRES (BAST FIBRES) :

Found along with other elements of phloem

Elongated & thick walled cells

Dead at maturity

Absent in primary phloem

1st formed primary phloem is known as protophloem

Later formed is known as metaphloem

Elements formed by fascicular cambium constitute secondary phloem

TISSUE SYSTEM IN PLANTS

• 3 tissue sysytems: (i) Epidermal tissue system (ii) Vascular tissue system (iii) Ground/ fundamental tissue system

(i) EPIDERMAL TISSUE SYSTEM• Forms outermost covering of plant body• Consists of epidermal cells, epidermal appendages &

stomata• Epidermis is outermost layer• Epidermis is single-layered• Each cell has small amount of cytoplasm & large

vacuole• Outer surface is covered with thick layer• Cuticle prevents loss of water from aerial part of plants• Epidermis is interrupted by small pores called stomata• Stoma is surrounded by 2 guard cells

• Guard cells are bean-shaped in dicot plants & dumb bell in monocots

• Outer wall is thin & inner wall is thick• They possess chloroplasts & carry out photosynthesis• Epidermal cells in their vicinity become specialised in their size

& shape• Stomatal apparatus – stomatal aperture, guard cells &

surrounding epidermal cells• Epidermis also bears appendages• Root hairs are unicellular elongation of epidermal cells of the

root• Appendages on stem epidermis are called trichomes• Help in preventing water loss by transpiration • Glandular/ secretory in many plants

(ii)VASCULAR TISSUE SYSTEM

• Includes xylem & phloem• They occur as discrete strands called vascular

bundles• Occur along same radius, vascular bundle is

called collateral• When strip of cambium is present b/w xylem &

phloem – open vascular bundle• No cambium in vascular bundle – closed

vascular bundle

• 2 phloem poles occur in a vascular bundle , separated from central xylem – bicollateral vascular bundle

• Xylem & phloem occur along different radii, alternating with each other – radial bundle

• When protoxylem is towards periphery & metaxylem is towards centre – exarch

• When protoxylem is towards centre & metaxylem is towards periphery - endarch

(iii) GROUND TISSUE SYSTEM

• Ground tissue – all tissues except epidermis & vascular bundles

• Consists of simple permanent tissues• Parenchyma cells present in cortex, pericycle;

pith & medullary rays• Ground tissue in leaves - mesophyll

My special thanx goes to my biology teacher Mrs Alermelu Natchair who gave and confirmed this permission and encouraged me to go ahead.