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Plant Tissues
Lesson Prepared Under MHRD project “National Mission on
Education Through ICT”
Discipline: Botany
Paper: Plant Anatomy
National Coordinator: Prof. S.C. Bhatla
Lesson: Plant Tissues
Lesson Developer: Dr. Arun Kumar Maurya and Dr. Anita Rani
Department/College: Dayal Singh College
Lesson Reviewer: Dr Basudha Sharma
Department/College: MM (PG) College,Modinagar, Uttar Pradesh
Language Editor: Dr Sonal Bhatnagar
Department/College: Hindu College
Lesson Editor: Dr Rama Sisodia, Fellow in Botany ILLL
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Plant Tissues
Table of Contents
Chapter: Plant Tissues

Introduction

Classification of Tissues

Simple tissue



Parenchyma

Distribution

Shape and arrangement

Structure and function

Synthetic parenchyma

Structural parenchyma

Boundary parenchyma

Transport parenchyma

Medullary parenchyma

Storage parenchyma
Collenchyma

Properties of collenchyma

Types of collenchyma

Functions of collenchyma
Sclerenchyma
°
°
Fibres

Properties of fibres

Distribution

Type of fibres

Function
Sclereids

Type of sclereids

Function
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Plant Tissues

Complex Tissue/ Vascular Tissue
°
°
Xylem

Tracheids

Vessel

Xylem parenchyma

Xylem fibres
Phloem

Sieve tube/Sieve cell

Companion cell/albuminous cell/strasburger cell

Phloem parenchyma

Phloem fibres

Summary

Glossary

Exercise

Multiple choice questions

References
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Plant Tissues
Introduction
Cell is the smallest functional unit of life. In complex multicellular organisms, cells similar
in structure and function are grouped together to form tissues. These tissues perform
various functions of organs necessary for maintaining biological life. Thus, the plant body
has a hierarchy of organs, tissues and cells.
Classification of Tissues
The wide variety in form and function of plant cells presents problems for the
classification of cell types, tissues and tissue systems. Sometimes different types of cells
have no well-defined boundaries between them and large numbers of intermediate forms
can be seen. There is a continuum from one type of cells to other types. Some cells
develop highly specialized, limited structures and functions, whereas others appear to
carry
out
multiple
functions
and
may
even
resume
growth,
cell
division
and
differentiation.
Some plant tissues are made up of only one type of cells called as “simple” tissues
whereas others are composed of different cell types called as “complex” tissue. Thus,
attempts have been made to classify tissues on the basis of mature structure, principal
cell or tissue origin etc. Classification of plant cells and tissues are therefore artificial and
should be viewed only for convenience of study and understanding.
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Plant Tissues
Figure: Diagrammatic representation of different types of plant tissues.
Source: http://lurnq.com/lesson/Anatomy-of-Flowering-Plants-Part-I-Tissues/
Tissues are made up of multiple cells having a common origin and all of them together
perform a similar or a set of similar functions. Depending on the capacity to divide,
tissues are classified into main types:
Meristematic tissues

Permanent tissues
Meristem is a group of actively dividing cells that do not form a specific organ but
retained the capacity to divide and form new cells. Meristematic cells are compactly
arranged without intercellular spaces. They are present at the apices of root and shoot
(apical meristem), between xylem and phloem (lateral meristem) and at leaf and node
bases (intercalary meristem) and do not store any reserve food material. All the
permanent cells formed are product of meristematic tissue that form specific tissue or
organ and are unable to divide after they attained a permanent shape and size. Plants
are composed of three types of tissue system: dermal, vascular and ground/fundamental
tissue. Each system is continuous throughout the plant body. (See next chapter)
Ground tissue is mainly composed of three basic cell types: Parenchyma, Collenchyma
and Sclerenchyma. Plant cells possess structural adaptations that make specific functions
possible and hence differentiate them from each other. This differentiation is evident
within the protoplast, cell contents and by modification of cell walls.
Simple Tissues
Parenchyma
Parenchyma (Para means “beside” and chyma means “infilling”) is a versatile ground
tissue that constitutes the “filler” tissue in soft parts of the plants. The term parenchyma
was first introduced by Nehemiah Grew in 1682 (Metcalfe, 1979). Ontogenetically
parenchyma is the precursor of other tissues. The body of the primitive organisms is
always parenchymatous. These cells when compared morphologically, developmentally
and physiologically with other complex tissues are found to be relatively undifferentiated
and unspecialized.
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Plant Tissues
Figure: A) meristematic, B) parenchyma, C) collenchyma and D) sclerenchyma cells.
Source: http://plantphys.info/plant_physiology/basiccytology1.shtml
Distribution
Parenchyma cells are present in almost all plant organs and forms the ground tissue in
which other tissues are embedded. They are present in the cortex, pith of roots and
stems, mesophyll of leaves, flesh of succulent roots, seed endosperm etc. Parenchyma
cells are also present in epidermis and vascular tissues.
Shape and arrangement
Parenchyma cells are generally polyhedral i.e. with many sides. Even if the parenchyma
cells are approximately isodiametric, they are not spherical but have many facets. Plant
cells rarely approach this ideal from because inside the tissue the pressure exerted is
uneven.
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Plant Tissues
Figure: Simple tissue: Parenchyma cells A) Transverse section B) Longitudinal section
Source:http://lurnq.com/lesson/Anatomy-of-Flowering-Plants-Part-I-Tissues/
The parenchyma cells are closely packed in the endosperm of seeds where they are
compactly arranged with no or few intercellular spaces. Storage parenchyma has
abundant intercellular spaces in aquatic plants forming aerenchyma. Leaf mesophyll cells
show extensive developed intercellular spaces, as a result of continued increase of cell
volume during growth, the number of walls faces increases above fourteen. This makes it
impossible for all the sides to remain in contact with all the sides of the neighboring cells
thus, the intercellular space develops. It develops in two ways:
By the separation of neighbouring cell walls, as in development of resin ducts in
Pinus, known as schizogenous cavity.

By the disintegration of the cells in the place where the space develops. Such
development is known as lysigenous development. It is seen in the formation of oil
cavities in the peel of citrus fruits.

In some cases spaces are formed by involving both the methods and the
development is called as Schizo-lysigenous development. The development of
intercellular spaces in protoxylem is formed by such method.
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Plant Tissues
Figure: A) Pinus needle showing schizogenous development of resin duct B) Peel of
Citrus fruit showing lysigenous development of oil gland or cavity.
Source:http://www.biologie.uni-hamburg.de/bonline/library/webb/BOT410/Secretion/PinuSecEpithelium400.jpg;B)
http://www.sbs.utexas.edu/mauseth/weblab/webchap9secretory/9.3-7.htm
Parenchyma cells may be elongated columnar in shape as found in palisade tissue of the
leaf. Stems of plants shows well-developed air spaces (Scirpus, petiole of Canna leaf)
with their stretched arms, such parenchymatous cells are called stellate parenchyma.
Parenchyma cells can be variously lobed e.g. spongy mesophyll and palisade parenchyma
of Helium and Pinus needle. Parenchyma cells may have folded projections e.g.
mesophyll of Xanthorrhoeaceae. Some parenchyma cells shows inner walls protuberance
for short distance transfer of solutes called as transfer cell such as nectaries, salt gland
etc. These protuberances increase the surface area for absorption or secretion. Such cells
are called as transfer cells.
Structure and function of parenchymatous cells
 It is least specialised plant cell.
 Thin and somewhat flexible primary cell walls.
 It is living at maturity and has a large central vacuole.
 It carries most of the plant metabolic function.
 Most parenchyma cells have the ability to resume meristematic activity and
differentiate into other cell types under special conditions like during repair and
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replacement of organs after injury, regeneration, formation of adventitious roots
and shoots union of grafts.
Lobed parenchyma
Figure: A) Transverse section of leaf of cattail (Typha) leaf showing stellate parenchyma.
B) T.S. of needle leaf of pine (Pinus) showing presence of lobed parenchyma cells (all the
red-stained cells).
Source:A)
http://www.sbs.utexas.edu/mauseth/weblab/webchap3par/3.3-6.htm
B)
http://www.sbs.utexas.edu/mauseth/weblab/webchap9secretory/9.3-6.htm
Parenchyma cells usually have thin primary walls, but thick primary walls may also exist
in some plants e.g. storage parenchyma cells of endosperm of Phoenix, Diospyros, Coffea
and Asparagus, have very thick walls with hemicellulose, getting accumulated there as
reserve substance. The walls of these cells gradually become thinner during germination
as the reserve substance is used by the developing embryo. Parenchyma cells may also
be induced to undergo lignification when infected by microorganisms suggesting the role
in disease resistance.
Parenchyma tissue is involved in almost all the physiological function of plant such as
storage of food, provide turgidity to the softer parts and helps in slow conduction of
various substances. They are known to perform specialized functions for which these cells
undergo various modifications. As parenchyma cells shows various functions and
structural modification these can be classified into various types:-
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Synthetic parenchyma
Synthetic parenchyma cells are that synthesizes something:

Photosynthetic: These are chlorophyll containing cells so called as chlorenchyma.
It is found in the mesophyll leaves, some young stems, succulent stem, primitive
plants, herbaceous plant etc. Mesophyll tissue is differentiated into compactly
arranged columnar cells called as palisade and loosely arranged tissue called
spongy parenchyma. Chlorenchyma cells are characterised by conspicuous vacuole
and the cells have air spaces between them (lacunate) e.g. T.S. Nerium leaf.
A
B
Figure: A) T.S. of Nerium leaf showing photosynthetic parenchyma cells showing both
palisade and spongy parenchyma; B) Meristematic cells are parenchyma cells that are
composed of immature cells with no intercellular spaces with abundant cytoplasm and
one or more nuclei.
Source:http://botit.botany.wisc.edu/Resources/Botany/Shoot/Leaf/Syringa/Cross%20Sec
tion/Palisade%20parenchyma%20MC.jpg.html;B)
http://commons.wikimedia.org/wiki/File:Mitosis_(261_13)_Pressed;_root_meristem_of_o
nion_(cells_in_prophase,_metaphase,_anaphase,_telophase).jpg

Meristamatic: These are immature cells contain abundant cytoplasm with one or
more nuclei. They are parenchyma cells that consist of a group of cells which
remain in continuous state of division or retain their power of division. They do not
have intercellular spaces. The vacuoles are small or absent. These cells may
differentiate into collenchyma and sclerenchyma or may stay as parenchyma.
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Plant Tissues

Secretory: Such parenchyma cells secrete substances and have dense protoplasts.
They may contain plenty of ribosomes; golgi bodies or ER depending upon their
secretion.
Structural parenchyma
 This includes ground tissue, pith and cortex which is non-photosynthetic in nature.
Figure: T.S. stem of Medicago showing ground tissue.
Source:http://botit.botany.wisc.edu/Resources/Botany/Cells%20and%20Tissues/Medicag
o/Labelled%20Medicago.jpg.html
 Aerenchyma: These are specialized parenchyma cells with large air spaces and
cavities, such parenchyma tissue is known as aerenchyma. The aquatic plants
provides buoyancy because of the aerenchyma in the cortex and through this the
plant can float on the surface of water and also gaseous exchange takes place for
e.g. leaf of Nymphaea, Hydrilla and Myriophyllum. Ethylene accumulates in
waterlogged tissue and this gas induces programmed cell death and formation of
aerenchyma. It may also be formed constitutively with no environmental stimulus
e.g. rice roots.
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Plant Tissues
Figure: A) T.S. of Nymphaea leaf showing aerenchyma tissue; B) T.S. stem of
Myriophyllum showing aerenchyma cells in the cortex region; C) T.S. of adventitious
roots of (a) rice and (b) maize taken 50 mm from the root apex and showing lysigenous
aerenchyma formation. Note the cubic cell packing in the rice cortex contrasting with the
hexagonal packing in maize (Micrographs courtesy E. Armstrong).
Source:A)http://student.nu.ac.th/cherrycoke/lesson6.htm;
B)://www.uri.edu/cels/bio/plant_anatomy/26.html
C)http://plantsinaction.science.uq.edu.au/edition1/?q=content/18-1-2-adaptiveresponses-waterlogging
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Boundary parenchyma
 Epidermis: It is the outer most layer in plant. Outer surface of epidermal cells has a
layer called cuticle which is made up of waxy substance called cutin, due to this cuticular
layer rate of transpiration is reduced.
Figure: A) T.S. of leaf (a portion enlarged) showing epidermal cell covered by thick
cuticle. B) Diagrammatic representation of endodermal cells bearing casparian strips
which prevents the entry of substances into the vascular bundles.
Source:http://www.studyblue.com/notes/note/n/midterm-1-definitions-withpics/deck/6021799; B) http://www.studyblue.com/notes/note/n/midterm-1-definitionswith-pics/deck/6021799
 Endodermis: Inner most layer of the cortex in stem and roots is called as endodermis. It
has a casparian strip around each cell which is made up of suberin. Endodermal cell
prevents the entry of substances into the vascular cylinder.
Figure: A) T. S. of Psilotum nudum rhizome haplostele (triangles indicate position of
endodermis) B) T. S. root of Smilax showing exodermis.
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Plant Tissues
Source:A)http://www.phytoimages.siu.edu/imgs/Cusman1/r/Psilotaceae_Psilotum_nudum
_41759.html;
B) http://phytoimages.siu.edu/imgs/Cusman1/r/Smilacaceae_Smilax_sp_46545.html
 Exodermis: The cells of exodermis is similar to endodermis but one or more cell in depth
in some roots, a type of hypodermis, the walls of exodermis may be suberized and /or
lignified for e.g. In Smilax it is sclerenchymatous.
Transport parenchyma
The parenchymatous
cells associated with xylem
or phloem
is meant
for the
transportation of water, minerals and food particles are known as transport parenchyma.
Figure: T. S. stem of Cucurbita pepo showing primary xylem and phloem (the arrow
indicates a sieve plate).
Source:http://www.phytoimages.siu.edu/imgs/Cusman1/r/Cucurbitaceae_Cucurbita_pep
o_45623.html
Transfer cells with wall ingrowths called a labyrinth. In a variety of tissues where
transport of solutes over short distances i.e. active transport or facilitated transport is
required, surface area including cell membrane increases by wall ingrowths e.g.
haustorial cells in parasitic plants such as Cuscuta.
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Plant Tissues
Figure: Cuscuta campestris: haustorium penetrating host tissues.
Source:http://www.phytoimages.siu.edu/imgs/Cusman1/r/ConvolvulaceaeCuscuta_camp
estris_47184.html
Medullary parenchyma
 It is found radially arranged in between the vascular bundles in the stem and is meant
for storage of reserve food.
Storage parenchyma
It occurs in many plants parts such as tubers, fruits etc. The parenchymatous cells of
plastids which store starch is called amyloplasts. In petals of flowers the plastids become
chromoplasts. Reserve materials are stored in parenchyma cells, i.e. in form of fluid in
the vacuoles (e.g. amides and proteins) or in the form of small solid particles (starch,
proteins, oils, fats etc.) or liquid in the cytoplasm.
 Cell sap presents in the roots cells of sugar beet and bulb scales of Allium cepa store
amides, proteins and sugars. Cotyledonary cells of many species of legumes show
proteins and starch grains in the cytoplasm.
 Parenchyma cells may be involved in the storage of water as in succulent plants. Such
cells are usually large, thin walled with a thin layer of cytoplasm. The vacuole has
somewhat mucilaginous sap which increases water holding capacity of the cell.
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Plant Tissues
 Tannins may also be present in parenchyma cells, such cells may be scattered in the
plant or may form continuous system. Tannin are found in vacuole. Parenchyma cells
may store mineral substances in the form of crystals.
Figure: Parenchyma cell showing A) chloroplast and B) chromoplasts C) starch grains
(bean cotyledons)
Source: http://student.nu.ac.th/cherrycoke/lesson6.htm
B) http://www.studyblue.com/notes/note/n/midterm-1-definitions-withpics/deck/6021799
C) http://www.uri.edu/cels/bio/plant_anatomy/27.html
Collenchyma
Collenchyma (Greek word “Colla” means “glue”) is another group of simple tissue
consisting of living cells found in plants. The first use of "collenchyma" was by Link
(1837)
who
described
it
as
the
sticky
substance
found
in
the
pollens
of
plants Bletia (Orchidaceae). Later on the term collenchyma was coined by Schleiden
(1839). Collenchyma cells are elongated, soft pliable cells with non-lignified thickened
primary walls. Sometime collenchyma cells contain numerous chloroplasts. Due to the
presence of thick wall it has specialized to function as supporting tissue. Collenchyma
cells retain active protoplast capable of removing the wall thickening when the cells are
induced to resume meristematic activity.
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Plant Tissues
Properties of collenchyma
Cell wall of collenchyma in addition to cellulose contains large amounts of pectin and
hemicelluloses without lignin deposition. Presence of pectin makes them hydrophilic and
helps in retaining much water. Ultrastructural detail shows presence of cross poly
lamellate or helicoidal structure in collenchyma wall with primary pit fields. Collenchyma
cells are known to possess several pattern in their wall thickening which can be seen
either in the corners of the cell, inner and outer tangential wall or on two opposite wall.
A
B
Figure: collenchyma cell A) transverse section B) longitudinal section.
Source:http://lurnq.com/lesson/Anatomy-of-Flowering-Plants-Part-I-Tissues/
Types of collenchyma
On the basis of thickening on tangential wall, three types of collenchyma cells are found
such as plate or lamellar, angular and lacunar/lacunate collenchyma.
Figure: Types of collenchyma cells.
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Source: http://student.nu.ac.th/cherrycoke/lesson6.htm
 Lamellar or Plate collenchyma
When the wall thickening is mostly restricted to the tangential wall called as lamellar/
plate collenchyma. They are found in stem cortex of Sambucus nigra, Sanguisorba,
Rheum and Eupatorium and in the petiole of Cochlearia armoracia.
Figure: A) T.S of Sambucus stem showing Lamellar collenchyma B) Angular collenchyma
in petiole of Cannabis
Source: A) http://www.uri.edu/cels/bio/plant_anatomy/34.html
B)http://www.doctortee.com/dsu/tiftickjian/cseimg/botany/plant-anat/stem/cannabisstem-xs.jpg
 Angular Collenchyma
Angular collenchyma cells are those in which the wall thickening is restricted to the
corners of cells and can be seen in the stem of Atropa belladonna, Solanum tuberosum
and petiole of Begonia, Beta, Coleus, Cucurbita, Morus, Ricinus Vitis, Cannabis and Celery
(Apium graveolens).
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Figure: Angular collenchyma in Celery petiole
Source: http:// www.doctortee.com/dsu/tiftickjian/plantanat/collenchyma
 Lacunar Collenchyma
In above two types intercellular spaces are absent but some time space gets developed in
the angular type of collenchyma that give rise to special type of collenchyma known as
lacunar / lacunate collenchyma e.g. are seen in adventitious root of corn, stem cortex of
Brunellia and Salvia and also present in members of Asteraceae and Malvaceaae.
Figure: A) Lacunar collenchyma from adventitious root of corn B) Annular collenchyma
located below the central vascular bundle of the leaf
Source:
A)
https://www.etsy.com/listing/80113232/pink-corn-root-8-x-10;
B)
http://www.ujaen.es/investiga/atlas/atlas_ingles/hojaolivo/hojaolivo100x3colenquima.ht
m
 Annular collenchyma
The annular collenchyma is characterized by cell wall that is more uniformly thickened
and lumen is more or less circular in outline. It can be distinguished from angular
collenchyma on the basis of degree of wall thickening restriction to the corners of cell.
Angular collenchyma shows thickening only at the corner but in annular, thickening
becomes massive and identity at corner thickenings becomes indistinguishable. Thus, the
lumen assumes a circular outline in contrast to angular type collenchyma. Collenchyma
cells show simultaneous increase in thickening and surface area. The cell wall may
become modified in the older plant or can modified into sclerenchymatous cells by
deposition of lignified secondary wall bearing simple pits.
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Plant Tissues
Functions of collenchyma
 The collenchymas provide flexibility, elasticity, mechanical support and strength to the
tissue.
 It also plays an important role in photosynthetic activities due to the presence of
chloroplasts.
Sclerenchyma
Sclerenchyma is a specialized tissue consisting of a group of cells in which secondary
walls are often lignified. The term Sclerenchyma is derived from the Greek word ‘skleros’
means ‘hard’ and ‘enchyma’, an ‘infusion’. The term sclerenchyma was coined by
Mettenius in 1805 and the cells are known as sclerenchymatous cells. Sclerenchyma cells
may or may not retain their protoplast at maturity. On the basis of length, sclerenchyma
cells are of two types; fibres and sclereids. Usually the fibres are long while sclereids are
short sclerenchyma cells.
Fibres
Fibres are long, spindle shaped cells with thick secondary wall and occur as strands in
plant. They exist as overlapping structure and impart strength to the fibre bundles.
Rutting is the process for fibres extraction from plant body which separates the fibre
bundles from associated non-fibrous cells. It is carried out in pond and this process is
hastened and assisted by microorganisms.
Properties of fibres
The fibre cells have presence of high lignin content and absence of pectin and cellulose,
their walls are not much hydrated or they have very less affinity for water. This property
makes wall more elastic in nature than plastic. Fibres possess simple pits whereas border
pits are relatively scarce.
Distribution
Fibres are distributed in plants as separate strands either in cortex and in phloem or as
sheath or bundle caps associated with the vascular bundles or may be grouped or
scattered in xylem and phloem. Monocot and dicot fibres show several characteristic
patterns. In Poaceae, fibres form a system having the shapes of a ribbed hollow cylinder
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Plant Tissues
with the ribs connected to the epidermis. Vascular bundle have prominent sheaths of
fibres and the peripheral bundles may be irregularly fused with each other or united by
sclerefied parenchyma into a sclerenchymatous cylinder for e.g. Zea mays, Saccharaum,
Andropogon, Sorghum.
Figure: Showing location of different types of fibres
Source: http://student.nu.ac.th/cherrycoke/lesson6.htm
Type of fibres
In angiosperms fibres are located in stem as outermost part of the primary phloem as an
astomosing strands or tangential plates. On the basis of their position in plants they have
been kept in two groups, xylary (intraxylary) and extraxylary fibres. The fibres present in
xylem are called xylary or intraxylary fibres. Xylary fibres are also known as wood fibre
and are of following types:
a)
Libriform fibres
b)
Fibre tracheids
c)
Septate fibres
d)
Mucilage fibres
These libriform and fibre tracheids are classified on the basis of type of pits present on
their walls. Libriform fibre (Latin Liber means inner bark) is longer and possesses simple
pits whereas fibre-tracheids are shorter with bordered pits.
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Plant Tissues
Figure: Quercus maceration showing fibre-tracheids and libriform fibres
Source: http://images.botany.org/set-17/17-104h.jpg
Fibre cells generally loses their protoplasm and become dead at maturity but in many
woody plants fibre retain their protoplasm and act as storage cell for carbohydrate and
convert them into sugars when plant requires. Otherwise, their prime function is to
provide mechanical support. Septa or cross wall formation takes place in phloem or
xylem fibre of dicot species that undergoes regular mitotic division after secondary wall is
deposited which leads to partitioning of fibre into two or more compartment. Such fibres
are known as septate fibre. These fibres not only occur in dicot but also in some
monocots such as Palmae and Bambusoideae. These fibres are non-vascular in origin.
The septa include a middle lamellae and two primary wall that may or may not be
lignified and remain in contact. The septate fibres of bamboos are characterized by thick
polylamellate secondary walls with additional secondary wall lamellae. Septa of the fibre
containing protoplast are interconnected by plasmodesmata, thus indicating role of septa
in support and in addition to it they perform the storage function because they contain
starch grains and sometimes crystals of calcium oxalate.
Sometime fibre also contains gelatinous layer (G layer) which makes the innermost
secondary wall layers, it contains high cellulose content but lignin is absent that
distinguishes it from the outer secondary wall layers. Presence of cellulose makes the G
layer hygroscopic and thus it swells up by absorbing large amount of water, it may
occlude the lumen of the cell and upon drying it pulls away from the rest of the wall.
They are also called as reaction fibre or mucilage fibre. These fibres are neither strictly
xylary nor extarxylary as they have been found in xylem and phloem of roots, stem and
leaves of dicots and in nonvascular tissue of monocot leaves. The role of G layers in
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Plant Tissues
leaves may be to assist in the maintaining the orientation of leaves with respects to
gravity and display of the leaflet to the sun.
Extarxylary fibres are located outside the xylem and these are of three types:
a)
Phloem fibres
b)
Pericyclic or perivascular fibre
c)
Cortical fibre
Phloem fibres
Phloem fibre also known as bast fibre which originates in early part of primary phloem
but functions as fibres after their primary function i.e. conduction ceases and thus called
as primary phloem fibre or protophloem fibre. Other examples of primary phloem fibre
are stem of Sambucus (elderberry), Tillia (Basswood), Liriodendron (Tulip tree), Vitis
(Grape vine), and Robinia pseudoacacia (Black locust). Flax fibres (Linum usitatissimum)
exist as single band with several layers in depth and are located on the outer periphery of
vascular bundle. When fibres are located within the secondary phloem called as
secondary phloem fibres. Soft fibres are obtained from phloem fibre of eudicots and
represent the bast fibre of commerce. They are soft, flexible and may or may not be
lignified. The example of bast fibres are hemp (Cannabis sativa) used in cordage, jute
(Linum usitatissimum) and remie (Boehmeria nivea) used in textile.
Pericyclic or Perivascular fibre
Perivascular fibres are extraxylary fibre found in stems of dicots, located in the periphery
of vascular bundles inside the innermost cortical layer as in Aristolochia and Cucurbita.
Extraxylary fibres also include the fibre of the monocot whether or not associated with
the vascular bundles. They often have thick cell wall and variability seen in lignin
deposition on cell walls.
Cortical fibres are extraxylary fibre found in stem and originate in cortex e.g. Barley.
Cortical fibre gives mechanical strengths to the plant body.
The fibres obtained from monocots are basically obtained from leaves and are hard and
stiff in nature, and thus they are called as hard or leaf fibre. In contrast to soft fibre, hard
fibres are rich in lignin present on walls, for e.g. abaca or manila hemp (Musa textilis),
bowstring hemp (Sansevieria sp.) and newzeland hemp (Phormium tenax). All of them
are used in cordage making. Henequen and Sissal (Agave sp.) is used in cordage and
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Plant Tissues
coarse textile. Pineapple fibre (Ananas comosus) is used in textile. The plants like maize
(Zea mays), sugarcane (Saccharum officinarum) and esparto grass (Stipa tenacissima)
are used for making paper whereas leaf fibres in the xylem as raw material.
Figure: The broken ring of perivascular (extraxylary) fibres in Aristolochia.
Source:http://www.biologie.unihamburg.de/bonline/library/webb/BOT410/410Labs/Labs
HTML-99/Stems-2/Labstm2-99.html
Some cells in plants are not fibre but they act as fibre and thus are included in fibre such
as cotton fibre which are obtained from the epidermal hairs of the seed of Gossypium.
Some plant structure can also be used as fibre such as stem of rattan (Calamus palm)
and Raffia is composed of leaf segments of raffia palm.
Sclereids
The term sclereid was coined by Tschierch in 1885. They are short sclerenchyma cells
having thick and strongly lignified secondary walls with many simple pits. The secondary
walls are multilayered. Some sclereids have thin secondary wall and contain living
protoplast at maturity. Sclereid protects soft plant tissue from herbivores or mechanical
damage.
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Plant Tissues
Type of Sclereids:
Depending upon the basis of size and shape of sclereids, they have been classified into
five main groups,
a)
Brachysclereids or stone cells
b)
Macrosclereids
c)
Osteosclereids
d)
Astrosclereids
e)
Trichosclereids
Brachysclereids
Brachysclereids are also known as stone cells. These are isodiametric or elongated cells
and are distributed widely in cells of cortex, phloem and pith of stem and are also found
in the flesh of food. They are present in fruits of Prunus, quinace (Cydonia); elongated
sclereids are present in the endocarp region of apple seeds and stone fruits (Drupe);
exocarp region of fruits of Manilkara achras; pulp portion of Mimusops elangi and Psidum
guajava, cortex region of Cinnamomum zeylanicum and exocarp region of Moringa
olefera.
Macrosclereids
Macrosclereids are elongated and rod like sclerenchyma cells which form palisade like
epidermal layer in seed coats of legumes. They are well developed in exocarp region of
Malus sylvestris.
Osteosclereids
Osteosclereids are columnar in shape but their ends become enlarge in such a way that it
appears bone like structure. They are well distributed in the sub-epidermal layer of seed
coat of some plants e.g. adaxial leaf surface of Nymphaea nouchali, Phillyrea latifolia,
Hakia and Osmenthus contain osteosclereids.
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Plant Tissues
Figure: A) Fruit of Prunus showing Brachysclereids B) magnified stone cell (sclereid)
from the juicy mesocarp of a 'Bartlett' pear C) Maceration of bean seed coat showing
macrosclereids
D)
W.M.
of
Osteosclereids
E)
T.S.
leaf
of
Nymphaea
showing
astrosclereids F) Banana leaf clearing showing trichosclereids.
Source: A) http://lurnq.com/lesson/Anatomy-of-Flowering-Plants-Part-I-Tissues/
B) http://waynesword.palomar.edu/ecoph17.htm
C) http://www.uri.edu/cels/bio/plant_anatomy/39.html
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Plant Tissues
D)
http://www.biologie.unihamburg.de/bonline/library/webb/BOT410/anatweb/images
/ParColSclr/MacroSclerEtc.jpg
E) http://www.biologie.uni-hamburg.de/bonline/library/webb/BOT410/anatweb/images/ParColSclr/NymphLfXSLive2Scler.jpg
F) http://botweb.uwsp.edu/anatomy/images/schlerenchyma/pages/Anat0040.htm
Astrosclereids
When the central body of cell develops arms or lobes like extension giving appearance of
star are known as astrosclereids. They are found in leaf of eudicot, adaxial surface of leaf
of N. cristata.
Trichosclereids
Tricosclereids are thin walled sclereids resembling hairs with branches. They are found on
the adaxial surface of leaves of Olea europea and Banana leaf.
Besides this two additional types of sclereids are also reported in plants:
Filiform sclereids are long cylindrical cells similar to fibres and are found in palisade
and spongy parenchyma of olive (Olea europaea) leaf.
Figure: Filiform sclereid in leaf of Olea europaea.
Source: http://images.botany.org/set-17/17-060h.jpg
Fibre sclereids are the fibre that differentiates in phloem and have characteristic of both
fibre and sclereids and thus named as fibre sclereids. They have been reported in
secondary phloem of root and shoot of the rosette leaves of Arabidopsis thaliana.
Sclereids are distributed in almost every organ of plant body ranging from epidermis,
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Plant Tissues
ground tissue to vascular tissue and occur singly or in cluster. When they occur as singly
they are known as idioblast.
Dicot leaves are rich in variety of sclereids but are absent in monocots. Two pattern of
distribution of sclereids are mainly observed in dicots; terminal pattern and diffuse
pattern. In terminal pattern they are confined to ends of small veins as seen in Hakea,
Mouriria, Boronia and Arthrocnemum whereas, in diffuse pattern either they occur either
solitary or in groups dispersed throughout the tissue without any spatial relationship to
the vein endings. The examples of diffuse pattern are seen in Olea, Osmanthus,
Pseudotsuga and Trochodendron.
Foliar structure as found in clove scale of garlic (Allium sativum) the sclereids forms part
of the entire epidermis. The plant species having well developed intercellular spaces or
air chambers possess trichosclereids such as Monstera deliciosa, Nymphaea (water lily)
and Nymphaea (Yellow pond lily).
Seeds contain seed coat which is hard and this hardness is due to development of
secondary wall in the epidermis and in the layers or layers beneath the epidermis e.g.
seeds of bean (Phaseolus), pea (Pisum), soybean (Glycine max) contain columnar
macrosclereids in epidermis and osteosclereides beneath the epidermis. The seed coat of
coconut (Cocos nucifera) contains ramiform pitted sclereids.
Figure: Stone cells or sclereids
Source: http://student.nu.ac.th/cherrycoke/lesson6.htm
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Plant Tissues
Functions
Sclereids provide mechanical strengths and plays important role in guiding light within
mesophyll. They are responsible for gritty texture found in some fruits like pear.
Complex tissue/ Vascular Tissue:
A tissue that consists of several kinds of cells which functions together is called complex
tissue. Xylem, phloem and vascular cambium (absent in monocot and lower plants) are
example of complex tissue as they are involved in the water-conduction, transport of
solutes and food material and are known as vascular tissue. The vascular plants also
referred to as tracheophytes, which include seedless vascular plants of Lycopodiophyta
(horsetails),
Pteridophyta
(ferns),
gymnosperms
and
angiosperms.
The
terms
tracheophyte (vascular plants) is given because of to the characteristic conducting
element present in the xylem tissues known as the tracheary elements.
Figure: Components in open and closed type of vascular bundles.
Source: http://bioict.exteen.com/
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Plant Tissues
Figure: A) Detailed structure of closed type vascular bundle B) Vascular bundle from
Ranunculus stem (open type)
Source:A)http://botit.botany.wisc.edu/Resources/Botany/Shoot/Stem/Zea%20stem/Vasc
ular%20Bundle%20MC%20.jpg.html
B)http://www.uri.edu/cels/bio/plant_anatomy/106.html
Xylem
Xylem (Greek word ‘xylos’= wood) is an example of complex tissue forming a part of
vascular tissue. The term xylem was introduced by Nägeli in 1858. Xylem is mainly
responsible for the conduction of water and mineral salts from roots to rest of the plant.
Two type of xylem tissue have been demarcated in plants - primary xylem and secondary
xylem. If the origin of xylem tissue has occurred from procambium of apical meristem, it
is called as primary xylem and if it has occurred from vascular cambium the xylem is
called as secondary xylem. The primary xylem develops early in the life of plant than
secondary xylem. Presence and absence of cambium in vascular bundle develops open
and closed type of Vascular bundles respectively. Xylem tissue consists of four kinds of
cells –
a) Tracheids
b) Vessels or tracheae
c) Xylem fibres
d) Xylem parenchyma
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Plant Tissues
The term tracheid is derived from “trachea” because of its resemblance with insect
tracheae. There are two types of tracheary elements in xylem, tracheids and vessel
elements. Both are nonliving at maturity and more or less elongated cells. They have
lignified secondary walls.
The primary xylem develops earlier and are first formed elements called as protoxylem
(from the Greek proto, first) and a later formed part are called as metaxylem (from the
Greek meta, after or beyond). The protoxylem differentiates in parts of primary plant
body where growth and differentiation has not yet completed. The protoxylem usually
contains few tracheary elements (tracheids or vessel). The metaxylem begins to
differentiate in the growing primary plant body and gets mature after elongation is
completed and it contains more tracheary elements.
Figure: Ranunculus root vascular cylinder showing the metaxylem (central last maturing
xylem) with fully formed lignified secondary cell walls.
Source:http://www.lima.ohiostate.edu/biology/archive/roots.html
The secondary xylem is formed by a complex meristem known as vascular cambium,
consisting of vertically elongated fusiform initials and squarish or horizontally (radially)
elongated ray initials and such development distinguishes it from the architecture of
primary xylem. The composition of secondary xylem found is more complex than the
primary xylem in having a wider variety of cells in the angiosperms.
Tracheids
Tracheids are elongated cell with blunt ends, present along the long axis of the plant
system. Phylogenetically the tracheids are most primitive type of cell found in xylem.
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Plant Tissues
These are imperforate or non-perforate cells having only pit-pairs on their common walls
with lignified secondary wall. Tracheids are imperforate cells with bordered pits on their
end walls. The tracheids contain simple pits along with bordered pits. They are arranged
one above the other and are present in both primary and secondary xylem with broader
lumen than that of fibres. This broader lumen in tracheids and occurrence of the pits
helps in water conduction with dissolved mineral salts by acting as conduits in vascular
plants. The presence of thick hard and lignified wall offer mechanical support to the
plants. Sometimes an intermediate type of cell element is also found in vascular system
known as fibre-tracheids (for detail consult fibre topic).
Figure: Components of xylem (vessel, tracheids and fibre with secondary thickening)
Source:http://elte.prompt.hu/sites/default/files/tananyagok/plants_fungi/ch04s04.html
The walls of tracheid are moderately thick and show different types of cell wall thickening
due to the deposition of secondary wall substances such as lignin. The bordered pits in
tracheary elements show three main types of arrangement Scalariform pitting: Where elongated pits are arranged parallel to one another
to form a ladder-like pattern, this pattern is called scalariform pitting.

Opposite pitting: Circular or oval bordered pits arranged in horizontal pairs
characterize opposite pitting. If such pits are crowded, their borders assume
rectangular outlines in face view.

Alternate pitting: When the pits are arranged in diagonal rows, this arrangement
is called as alternate pitting, and their crowding results in borders that are
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Plant Tissues
polygonal (angular and with more than four sides) in outline and is most
commonly found in dicots.
Figure: Tracheids showing A) scalariform B) opposite and B) alternate pitting.
Source: A) http://delta-intkey.com/wood/en/www/aquil-ho.htm
B) http://blackwalnut.npust.edu.tw/archives/wood/133477;
C) http://blackwalnut.npust.edu.tw/archives/wood/133478
Vessels
Vessels or trachea are elongated tube like structure arranged in longitudinal series. The
vessels are variable in length and its lengths are positively correlated with its diameters.
Wide vessels are longer and narrow vessels are shorter. The longest vessels are found in
the early wood of ring porous species of dicots in which the vessels (pores) of the firstformed wood (early wood) are especially wider. The large-diameter vessels have been
found to extend throughout the entire length of tree’s stem but most of them were much
shorter. The largest reported vessel element are approximately 3 meter in ash plant
(Fraxinus excelsior; family Oleaceae), 18 meters in Fraxinus americana , 10.5 to 11.0
meters in Quercus rubra and smallest one is 60 cm found in Acer.
Unlike tracheids, vessels are perforated at end walls except at the terminal end of vertical
axis. The lumen of vessel is wider than that of tracheids. Vessel elements have
perforations at both end through which vessel elements are interconnected. The
imperforations are areas lacking both primary and secondary walls. The part of vessel
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Plant Tissues
element wall bearing the perforation or perforations is called perforation plate. The
perforations also occur on the lateral wall.
The vessel elements occur parallel to the long axis of plant body. The perforation plate
may be simple or multiple one type. When due to dissolution of entire end wall, a single
pore is formed at the perforation plate known as simple perforation plate (Mangifera). On
the other hand, if the perforation plate has many pores, then it is called multiple
perforation plate (Liriodendron). The presence of simple type plate is characteristic of
advanced type of plants where dissolution of end wall is more or less complete.
Figure: A) L.S. of vascular bundles in spurge (Euphorbia) showing simple perforation; B)
Compound perforation plate
Source: A) http://www.sbs.utexas.edu/mauseth/weblab/webchap7xylem/7.3-5a.htm
B) http://www.sbs.utexas.edu/mauseth/weblab/webchap7xylem/7.3-7.htm
The secondary wall thickenings of vessels elements are seen as annular, spiral,
scalariform, reticulate or pitted as found in tracheids. Scalariform perforation plates are
formed when the perforation is elongated and are arranged in parallel series. When it is
formed in the form of network it is called as reticulate but when it is in circular form
called as foraminate perforation.
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Plant Tissues
Figure: (A) Acer saccharum wood, T. S. showing prominent reticulate pitting, vessels,
and multiseriate rays. (B) L. S. of corn stem (Zea mays) through a vascular bundle, with
phloem on the right, xylem on the left where xylem vessel elements with annular
secondary walls
Source:(A)http://images.botany.org/set-17/17-117h.jpg
(B)http://www.sbs.utexas.edu/mauseth/weblab/webchap7xylem/7.2-1.htm
Vessels are principal water conducting elements in angiosperms. Vessels are completely
absent in pteridophytes and gymnosperms (except Gnetum). The main function of vessel
is conduction of water and minerals along with mechanical support to the plant.
Xylem fibres
The fibres associated with xylem are known as xylem fibres. Xylem fibres are very much
elongated with tapering ends. The fibres are dead cells having lignified walls with narrow
lumen. They are present both in primary and secondary xylem. Xylem fibres or wood
fibre are two types
a) Fibres tracheids
b) Libriform fibres
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Plant Tissues
Fibre tracheids are intermediate forms between fibre and tracheids, possessing border
pits whose borders are not fully developed. Libriform fibres are narrow, having
obliterated lumen. They contain thick secondary wall with simple pits. They provide
additional mechanical support to the plant body. Modification of fibre-tracheids and
libriform fibres are seen as new form called as gelatinous fibres which are the common
components of reaction wood in dicots.
Xylem parenchyma
Living parenchyma cells associated with the xylem are known as xylem parenchyma. It is
the only living component found in xylem tissue. Xylem parenchyma cell wall is thin and
made up of cellulose. They act as storage house of starch and fat with assisting in
conduction of water.
Two forms the xylem parenchyma cells are present in the secondary xylem:
a)
axial parenchyma
b)
ray parenchyma
The axial parenchyma is the cells which are derived from the elongated fusiform initials of
vascular cambium, and their long axes are oriented vertically in root or stem. The ray
parenchyma cells are derived from the short ray initials of the vascular cambium. They
may have their long axes oriented either vertically or horizontally with regard to the axis
of stem or root.
Figure: Showing axial and ray parenchyma in secondary xylem.
Source:http://www.cas.miamioh.edu/~meicenrd/ANATOMY/Ch5_CellTypes/parenchyma.
html
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Plant Tissues
When these two type of cells present in the secondary xylem there secondary walls are
well lignified. The pit-pairs are present between parenchyma cells. They may be
bordered, half-bordered, or simple but they are always simple. When some parenchyma
cells deposit thick secondary walls they are known as sclerotic cells, or sclereids.
The xylem parenchyma cells can store food reserves in the form of starch and fat. These
content shows rhythmic fluctuation that help in adaptation. In many deciduous trees of
temperate region, starch accumulates in late summer or early autumn but declines
during dormancy period. It is because low winter temperature favors conversion of starch
to sucrose which further acts as protecting agent during full dormancy against frost injury
and starch is again resynthesized at the end of dormancy.
Apart from fat and starch, tannins and crystals are also common inclusions. These
storage products help in identification of woods. The ray parenchyma cells in herbaceous
plants and young twigs of woody plants shows presence of chloroplasts.
The axial and the ray parenchyma cells are located adjacent to the vessels in the
secondary xylem. These parenchyma cells develop protrusions or balloon like structure
that enters through the pit cavities and into vessels lumen known as tyloses (singular:
tylose). The parenchyma cells that give rise to tyloses are called as contact cells. Contact
cell wall are characterized by less cellulose content but rich in pectin and deposited by
the protoplast after completion of secondary wall formation. This layer is called the
protective layer which is deposited on surfaces of the contact cell wall but is thickest on
the side of the cell bordering the vessel, especially at the pit membrane. In addition to
secondary xylem, tyloses also occur in primary xylem. The formation of tyloses, results in
ceased activity or functions of vessels.
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Plant Tissues
Figure: Showing tyloses in xylem vessels
Source:http://wwwplb.ucdavis.edu/labs/rost/virtual%20grape%20dreamweaver/Shoots
%20Secondary%203.html
Phloem
Phloem is also a complex tissue. It is the principal food-conducting tissue of vascular
plants and it also transports diverse range of substances such as sugars, amino acids,
micronutrients, lipids (primarily in the form of free fatty acids), hormones, floral stimulus
(florigen), proteins and RNAs.
Phloem plays an important role in inter-organ communication and coordination of growth
processes within the plant. Long-distance signaling in plants occurs mainly through the
phloem. Apart from food transport, a large amount of water is also transported through
them which serve as the principal source of water for fruits, young leaves, and storage
organs such as tubers.
Phloem is spatially associated with the xylem. Phloem may be classified as primary or
secondary on the basis of its time of appearance in relation to the development of the
plant or organ as a whole. The primary phloem is derived from the procambium of apical
meristem and initiated in embryo or young seedling is constantly added to during the
development of the primary plant body and completes its differentiation when the
primary plant body is fully formed.
The secondary phloem originates from vascular cambium and reflects the organization of
this meristem in its possession of axial and radial systems. The phloem rays are
continuous through the cambium with those of xylem, providing a pathway for radial
transport of substances between the two vascular tissues.
The primary phloem elements that develop first from the procambium are smaller in size
called the protophloem, whereas those develop later are larger in size called
metaphloem. The protophloem is short lived. It is crushed by the developing
metaphloem.
Primary and secondary phloem tissues contain the same types of cells but the
organization is different. The primary phloem is made up of one system without rays but
secondary phloem is organized into the axial and the radial system with rays.
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Plant Tissues
Phloem is composed of four kinds of cells.
a)
Sieve elements
b)
Companion cells
c)
Phloem parenchyma
d)
Phloem fibres
B
A
Figure: A) Showing components of phloem tissue B) Showing Sieve tube element,
companion cell and sieve plate.
Source:A)http://elte.prompt.hu/sites/default/files/tananyagok/plants_fungi/ch04s04.html
B) http://preuniversity.grkraj.org/html/3_PLANT_ANATOMY.htm
Apart from these four types of cells, fibres and sclereids are also common phloem
components. Sometimes laticifers, resin ducts, and idioblasts may also be present in the
phloem.
Companion
cells are present
only in
angiosperms
and
are
absent
in
pteridophytes and gymnosperms. Phloem fibres are absent in primary phloem of most of
angiosperms. But they are usually present in the secondary phloem.
Sieve elements
Sieve elements are main component of phloem because of the presence in their walls of
areas (sieve areas) penetrated by pores. Sieve elements can be segregated on the basis
of specialization into sieve tubes or sieve cells. Sieve tubes are more specialized but sieve
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Plant Tissues
cells are less specialized. The sieve tube forms a longitudinal series of sieve-tube
elements similar to vessel elements. Contrary to the vessel elements, the distribution of
sieve-tube elements is restricted only in angiosperms and use of term sieve cell is
restricted to gymnosperms.
The sieve elements of the seedless vascular plants, or vascular cryptogams, show much
variation in structure and development and are referred as sieve element. Young sieve
elements contain the entire cellular components characteristic of young plant cells. As
they differentiate, the sieve elements undergo profound changes.
Sieve tubes
Sieve tubes are long tube like structure and are formed from a row of cells arranged in
longitudinal series. The end wall of sieve tube cells shows sieve cell like perforation called
as sieve plate which establishes the connectivity with the neighboring sieve cell. The
protoplasts of sieve-tube elements contain P-protein (phloem protein or formerly called
as slime). The unique carbohydrate known as callose is associated with conducting sievetube elements and it is deposited there in response to mechanical injury, some kind of
stimulation. Callose normally accumulates at sieve plates and lateral areas and
disappears sometime after the sieve element dies. Callose apparently plays a role in
sieve-pore development.
Figure: L.S. of stem showing components of phloem tissue
Source:http://lurnq.com/lesson/Anatomy-of-Flowering-Plants-Part-I-Tissues/
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Plant Tissues
The sieve-tube elements are associated with companion cells which is a specialized
parenchyma cells. Thus it is called as sieve tube-companion cell complex or sieve
element–companion cell complex. It is closely related to the sieve-tube elements both
ontogenetically and functionally.
Sieve cells
The sieve cells are narrow elongated cells without conspicuous sieve areas. Sieve cells
possess more sieve area. Sieve cells have sieve areas on their lateral walls only and are
not arranged one above the other in linear rows. They are not associated with companion
cells. They are more primitive than sieve tubes and distributed mainly in lower vascular
plants and gymnosperms. Sieve cells have acted as precursor cell and give rise of sieve
tubes.
Companion cells
These are specialized thin-walled, elongated parenchyma cells intimately associated with
sieve-tube elements. Companion cells and sieve-tube elements are closely related
ontogenetically and derived from the same mother cell. In contrast to sieve elements, the
companion cell cytoplasm has a prominent nucleus and is connected to sieve tubes
through pits found in lateral walls. The companion cells are present only in angiosperms
and occur abundantly in monocots. Companion cells are absent in primitive dicots and in
primary phloem.
Gymnosperms and pteridophytes lack companion cell but have analogous cell known as
albuminous cell. It is also known as Strasburger cell and named after Eduard
Strasburger. The Strasburger cells show symplastic connections and have large median
cavities containing numerous elements of smooth tubular endoplasmic reticulum with the
sieve cells. In contrast to companion cells, the albuminous cells are smaller in size and
have different origin. They assist the sieve tubes in the conduction of food materials.
Phloem parenchyma
The parenchyma cells associated with phloem are called phloem parenchyma. These are
living cells with their cell wall rich in cellulose and primary pit fields. They are concerned
with storage of starch, fats, resins and tannins. The parenchyma cell of primary phloem is
elongated and is present with sieve elements along long axis. The parenchyma cell in
secondary phloem are two types, phloem parenchyma and ray cells. Former type is
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Plant Tissues
associated with vertical plane and later one is associated with horizontal plane. Usually
parenchyma cells are absent in monocots.
Phloem fibres
The fibres of sclerenchyma associated with phloem are called phloem fibres or bast
fibres. They are narrow, vertically elongated cells with thick walls and a narrow lumen
(the cell cavity). Among the four kinds of phloem elements, phloem fibres are the only
dead tissue. Phloem fibres are rare in pteridophytes and some spermophytes but occur
both in primary and secondary phloem. They functions as strengthening and supporting
cells.
Summary
Tissues are made up of multiple cells having common origin and together perform a
similar or a set of similar functions. These tissues perform various functions necessary to
maintain biological life. Meristematic tissues have similar cells that have retained their
capacity to divide and form new cells. These new cells lose the ability to form permanent
tissue. Some plant tissues are made up of only one type of cells called as “simple” tissues
whereas others are composed of different cell types called as “complex” tissue.
Parenchyma is a versatile ground tissue that constitutes the “filler” tissue in soft parts of
the plants. Parenchyma cells usually have thin primary walls. Parenchyma tissue is
involved in almost all the physiological function of the plant. They are involved in the
storage of food, provide turgidity to the softer parts and cortex of aquatic plant have
parenchyma cells with large air spaces and cavities.
Collenchyma is another group of simple tissue consisting of living cells found in plants.
These are elongated, soft pliable cells with non-lignified thickened primary walls. Due to
thick wall nature, it has specialized to function as supporting tissue. Cell wall of
collenchyma contain in addition to cellulose, large amounts of pectin and hemicelluloses
and without lignin deposition. On the basis of thickening on tangential wall, three types of
collenchyma cells are found such as plate or lamellar, angular and lacunar/lacunate
collenchyma.
Sclerenchyma is a specialized tissue consisting of a group of cells in which secondary
walls are lignified. On the basis of length, sclerenchyma cells have been kept in two
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Plant Tissues
groups; fibres and sclereids. Usually the fibre cells are long while sclereids are short cells.
Angiosperms
contain
fibres
in
stem
as
outermost
part
of
primary
phloem
as
anastomosing strands or tangential plates. On the basis of position of fibre in plant body,
they have been kept in two groups, xylary or intraxylary fibre and extraxylary fibres.
Fibres present in xylem are called xylary. Extarxylary fibres are located outside the xylem
and these are of three types; phloem fibre, pericyclic or perivascular fibre and cortical
fibre. Sclereids are type of sclerenchyma cells. They are short cells having thick and
strongly lignified secondary walls with many simple pits. The secondary walls are
multilayered. On the basis of size and shape of sclereids, they have been classified into
macrosclereids, brachysclereids, osteosclereids, astrosclereids and trichosclereids.
A tissue that consists of several kinds of cells but all of them function together is called
complex tissue. Xylem and phloem are example of complex tissue. They are involved in
the water-conduction, transport of solutes and food material, are known as vascular
tissue. Two type of xylem tissue have been demarcated in plants - primary xylem and
secondary xylem. Xylem tissue is consists of four kinds of cells namely tracheids, vessels
or tracheae, xylem fibres and xylem parenchyma. Phloem is also a complex tissue and
second important tissue present in vascular tissue. Phloem is composed of four kinds of
cells, sieve elements, companion cells, phloem parenchyma and phloem fibres. The
phloem is the principal food-conducting tissue of vascular plants.
Glossary
Angular
collenchyma:
It is a form of collenchymas in which the primary wall thickening is
most prominent in the angles where several cells are associated.
Astrosclereid:
It is a type of sclereid in which shows branching or ramification.
Brachysclereid:
It is also known as stone cell. It is short, roughly isodiametric sclereid
and resembling a parenchyma cell in shape.
Collenchyma:
It is supporting tissue composed of more or less elongated living cells
with unevenly thickened, nonlignified primary walls. Collenchyma is
prominant in regions of primary growth in stems and leaves.
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Plant Tissues
Companion cell: A specialized parenchyma cell associated with a sieve-tube element in
angiosperm phloem and arising from the same mother cell as the
sieve-tube element.
Lacunar
collenchyma:
A type of collenchymas tissue characterized by intercellular spaces and
cell wall thickenings facing the intercellular spaces.
Lamella:
A thin plate or layer.
Lamellar:
A type of collenchymas tissue in which cell wall thickenings are
deposited mainly on tangential walls.
Macrosclereid:
It is a type of sclereids which is elongated with unevenly distributed
secondary wall thickening and commonly found in seed epidermis of
Fabaceae.
Metaphloem:
It is a part of the primary phloem that differentiates after the
protophloem and before the secondary phloem.
Metaxylem:
It is a part of the primary xylem that differentiates after the protoxylem
and before the secondary xylem.
Osteosclereid:
It is a type of sclereids which is Bone-shaped and having a columnar
middle part with enlargements at both ends.
Parenchyma cell: Generally it is not a specialized cell having a nucleate protoplast and
associated
with
one
or
more
of the various physiological
and
biochemical activities in plants. Parenchyma cells are diverse in size,
form, and wall structure.
Phloem
parenchyma:
A type of parenchyma cells located in the phloem are referred as axial
parenchyma in secondary phloem.
Phloem:
It is main food-conducting tissue of the vascular plant and contains
sieve elements phloem parenchyma cells, fibres and sclereids.
P-protein:
It is a proteinaceous material found in Phloem especially sieve tube
elements.
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Plant Tissues
Primary phloem: When Procambium differentiates it give rise of phloem tissue during
primary growth and differentiation of a vascular plant. It is then
commonly
divided
into
the
earlier
protophloem
and
the
later
metaphloem.
Protoxylem:
It is the First-formed elements of the xylem.
Ray parenchyma: It is a type of parenchyma cells found in secondary vascular tissues.
Sclereid:
It is a sclerenchyma cell, short and thick lignified secondary walls with
many pits.
Sclerenchyma:
It is a type of tissue composed of sclerenchyma cells that includes
fibres, fibresclereids, and sclereids.
Sieve cell:
It is a type of sieve element that has relatively undifferentiated sieve
areas without sieve plates. Generally sieve cells are found in phloem of
gymnosperms.
Sieve element:
These are cell in the phloem tissue concerned with mainly longitudinal
conduction of food materials.
Sieve plate:
It is a part of the wall of a sieve-tube element bearing one (simple
sieve plate) or more (compound sieve plate) highly differentiated sieve
areas.
Sieve tube:
A
series
of
sieve-tube
elements
arranged
end
to
end
and
interconnected through sieve plates.
Sieve-tube
element:
It is one of the series of cellular components of a sieve tube. It shows a
more or less pronounced differentiation between sieve plates (wide
pores) and lateral sieve areas (narrow pores).
Strasburger cell: Few ray and axial parenchyma cells spatially are functionally associated
with the sieve cells resembling the companion cells of angiosperms.
These do not have common origin from the same precursory cells as
seen in the sieve cells and companion cells. They are also known as
albuminous cells and are mainly associated with gymnosperm phloem.
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Plant Tissues
Tissue:
It is a group of cells organized into a structural and functional unit.
Tissue system:
Structurally and functionally organized tissue or tissues in a plant or
plant organ into a unit is called as tissue system. In plants, commonly
three tissue systems are recognized, dermal, vascular and fundamental
(ground tissue system).
Tracheary
element:
water conducting cell, tracheid or vessel element found in vascular
system of plants.
Tracheid:
A tracheary element of the xylem. It has no perforations as found in
vessel element and may have any kind of secondary wall thickening.
Tracheids occur in primary and in secondary xylem.
Trichosclereid:
It is type of branched sclereid with hair-like branches extending into
intercellular spaces.
Tylose (pl. tyloses): It is an outgrowth from found in xylem where a parenchyma cell
(axial or one in a ray) through a pit cavity into a tracheary cell and
partially or completely blocking the lumen of tracheids.
Vascular tissue:
It refers to either or both vascular tissues, xylem and phloem.
Vessel:
It is a tube-like series of vessel elements and the common walls of
have perforations.
Vessel element:
It is one of the cellular components of a vessel.
Xylem elements: It is a cell composing the xylem tissue.
Xylem fibre:
A fibre of the xylem tissue.
Xylem:
It is a principal water-conducting tissue in vascular plants characterized
by the presence of tracheary elements.
Xylem ray:
Part of a vascular ray that is located in the secondary xylem.
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Plant Tissues
Exercises
Q.1. Distinguish between following pairs:
a) Paranchyma and Collenchyma tissue
b) Parenchyma and fibre cells
c) Xylem and phloem tissue
d) Companion and albuminous cell
e) Macrosclereids and osteosclereids
f) Bast fibre and surface fibre
g) Brachysclereids and Trichosclereids
h) Angular and lacunar collenchyma
i)
Cortical and Phloem fibre
j) Intraxylary and extraxylary fibre
Q. 2. Write short note on following topics:
a) Trachieary elements
b) Sieve tube
c) Trichosclerids
d) Strasburger cell
e) Sclereids
f)
Structural fibre
g) Sieve Cells
h) Phloem fibre
Q.3. Describe the general properties of parenchyma cells.
Q.4. What is sclereids and write its significance.
Q.5. Describe the type of tissue found in in angiosperms.
Q.6. Explain the collenchyma and write its importance in plant system.
Q.7. List the types of parenchyma tissue with examples.
Q.8. Discuss the types of fibre with suitable example.
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Plant Tissues
Q.9. Discuss the anatomical difference between tracheid and vessel of vascular plants.
Q.10. What is xylem parenchyma and write its function.
Q.11. Define collenchymas and describe the types of collenchyma with suitable examples.
Q.12. what is vascular tissue. Elaborate their components with their function.
Multiple Choice Questions
Q.1: Collenchymatous hypodermis is characteristic feature of
(a) Dicot stems
(b) Grass Stem
(c) Monocot stem
(d) Plant roots
Correct Answer:
(a) Dicot stem
Feedback for answer:
Collenchyma is present in the hypodermal region of dicot stem providing mechanical
support.
Resource/Hint/feedback for the wrong answer
Collenchyma is absent from roots and monocot plants
Q.2: Who gave the term tissue
(a) Hooke
(b) Charles Darwin
(c) Nageli
(d) N. Grew
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Plant Tissues
Correct Answer:
(d) Grew
Feedback for answer:
N. Grew coined the term tissue in 1682.
Resource/Hint/feedback for the wrong answer
Charles Darwin is known for many contributions in biology such as theory of evolution,
natural selection and origin of species.
Nageli coined the term meristem in 1858.
Hooke discovered the cell in cork slice via rudimentary microscope.
Q.3: A group of isodiametric cells with prominent intercellular space is called as
(a) Collenchyma
(b) Paranchyma
(c) Chlorenchyma
(d) sclerenchyma
Correct Answer:
(b) Paranchyma
Feedback for answer:
Paranchyma cells are basic type of cells are usually isodiamentric having 14 facets with
intercellular space.
Resource/Hint/feedback for the wrong answer
Chlorenchyma cells are modified parenchyma cells which have developed chlorophyll and
found in photosynthetic mesophyll cell.
Sclerenchyma cells are dead cells with thick lignifications meant for mechanical function in
plants.
Collenchyma cells are living cells with high deposition of cellulose and pectin at the corner
of cells.
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Plant Tissues
Q.4: A simple mechanical tissue rich in lignin is
(a) parenchyma
(b) sclerenchyma
(c) collenchyma
(d) chlorenchyma
Correct Answer:
(b) sclerenchyma
Feedback for answer:
Sclerenchyma cells are dead cells with thick lignifications meant for mechanical function in
plants.
Resource/Hint/feedback for the wrong answer
Collenchyma is living cells with high deposition of cellulose and pectin at the corner of
cells.
Parenchyma cells are isodiametric cells with prominent intercellular space.
Chlorenchyma cells are modified parenchyma cells which have developed chlorophyll and
found in photosynthetic mesophyll cell.
Q.5: Vascular bundles in a dicot stem are
(a) open, collateral and exarch
(b) closed, collateral and endarch
(c) closed, collateral and exarch
(d) open, collateral and endarch
Correct Answer:
(d) open, collateral and endarch
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Plant Tissues
Feedback for answer:
Dicot stem shows the presence of conjoint, collateral and open vascular bundles with an
endarch xylem.
Resource/Hint/feedback for the wrong answer
(a) Dicot stem vascular bundles are not open, collateral and exarch type
(b) Dicot stem vascular bundles are not closed, collateral and endarch
(c) Dicot stem vascular bundles are not closed, collateral and exarch
Q.6: Sieve tubes are suited for translocation of food because they possess
(a) bordered pits
(b) no ends walls
(c) broader lumen and perforated cross walls
(d) no protoplasm.
Correct Answer:
(c) Broader lumen and perforated cross walls.
Feedback for answer:
Sieve tubes are suited for translocation of food because they possess broader lumen and
perforated cross walls.
Resource/Hint/feedback for the wrong answer
Border pits are absent
They posses end walls known as sieve plates
They have protoplasm that lacks nuclei at maturity.
Q.7: Angular collenchyma occurs in
(a) Cucurbita
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Plant Tissues
(b) Helianthus
(c) Ipomoea
(d) Sombucus
Correct Answer:
a) Cucurbita
Feedback for answer:
Angular collenchyma occurs in Cucurbita. It has thickening at the angles and there are no
intercellular spaces. It is generally found in leaf petioles.
Resource/Hint/feedback for the wrong answer
Helianthus shows lamellar collenchymas in their stem
Sambucus stem shows lamellar collenchymas in their stem
Ipomoea stem shows lacunar collenchyma in their stem
Q.8: Bordered pits are found in
(a) Sieve cells
(b) Vessel wall
(c) Companion cells
(d) Sieve tube wall.
Correct Answer:
(b) Vessel wall
Feedback for answer:
Bordered pits are cavities in the lignified cell walls of xylem conduits (vessels and
tracheids) that are essential components in the water-transport system of higher plants.
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Plant Tissues
Resource/Hint/feedback for the wrong answer
Sieve cells are long, slender, conducting cells of the phloem don’t have bordered pits.
Companion cell are living cell associated with sieve tube cells in phloem in angiosperms
and don’t possess bordered pits.
Sieve tube wall lack bordered pits.
Q.9: Which of the following statement is not true about ‘sclereids’??
(a) These are groups of living cells.
(b) These are found in nut shells, guava pulp, pear.
(c) These are also known as stone cells.
(d) These are form of sclerenchyma with fibres.
Correct Answer:
(a) Sclereids are a type of sclerenchyma cells.
Feedback for answer:
Sclereids are a reduced form of sclerenchyma cells with highly thickened, lignified cellular
walls
Resource/Hint/feedback for the wrong answer
Sclerieds are found in nut shells, guava pulp, pear.
These are alternatively known as stone cells
Sclerieds are form of sclerenchyma with fibres.
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Plant Tissues
Q.10: Vessels are reported in
(a) All angiosperms and few gymnosperms
(b) Most of angiosperms and few gymnosperms
(c) All angiosperms, all gymnosperms and few pteridophyta
(d) all pteridophyta and bryophyta
Correct Answer:
(b) Most of angiosperms and few gymnosperms
Feedback for answer:
Vessels are long tubelike nonliving lignified structures meant for the conduction of water
and solutes.
Resource/Hint/feedback for the wrong answer
Vessels are found in the wood of almost all the angiosperms except certain primitive
members of the order ranales (vesseless dicots), e.g., Trochodendron, Tetracentron,
Drimys, Pseudowintera, etc.
Vessels also occur in the members of order Gnetales of gymnosperms (e.g., Genetum,
Ephedra and Welwitschia) and in some pteridophytes.
References
1. Esau, K. 1965. Plant Anatomy. Jhon Wiley and Sons Inc., New York.
2. Ray F. Evert. 2006. Esau's Plant Anatomy: Meristems, Cells, and Tissues of the
Plant Body: Their Structure, Function, and Development, Third Edition. Jhon Wiley
and Sons Inc., New York.
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Plant Tissues
3. Fahn, A. 1990. Plant Anatomy. Pergamon Press, Oxford.
4. William C. Dickison. 2000. Integrative Plant Anatomy, Academic Press.
5. V. Singh, P.C. Pande, D.K. Jain. 2005. Anatomy of Seed Plants, Rastogi
Publications, Meerut.
6. Websites motioned with Photographs and texts
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