EXPERIMENT 5.
STUDY OF PLANT
TISSUES
Structure
5.1 Introduction
Objectives
5.2 Materials Required
5.3 Observations on Simple Permanent Tissues
t Parenchyma
CcrUenchyma
0
Sclerenchyma
5.4 Observarions on Complex Pcrmanent Tissues
Xylem
phloem
5.1 INTRODUCTION
In the last exercise you had observed undcr the micrc~scope,the structure of
different types of animal tissues. Plant organs are aiso made of different types
of tissues. These tissues perform two important functions i) They provide the
mechanical strength to the plants and ii) conduct water, minerals and nutrients
to the various parts of the plant body. Plant tissues likc animal tissues are
composed of groups of cclls similar in origin, size and shapc, performing a
specific function. On the basis of their development plant tissues fall into two
categories, the ineristcmatic tissue and permanent tissucs. Thc fonncr are
immature undifferentiated tissues and the cclls are capable of division.
Permanent tissues are dcrivcd from the meristcm by gradual differentiation and
they are mature. Their cells do not divide. Pcmanent tissues fall into two
categories i) simple permanent tissues and ii) complex permanent tissues. Thc
first type is composed of similar homogenous cells. The second type is
composed of heterogenous cclls and are made of diffcrcnt typcs of cell
elements. In the lab exercise, you will be observing b e prcparaiions of different .
types of tissies under the microscope. Also you will sketch the structure of
. the tissues in your observation note book and become familiar with their
functions as well.
Objective
At ..the end of Ms exercise, you shall be able to
identify and describe lhc structure of different typcs of plant tissucs and
make sketches of them.
. dcscribe the lunctions of simple and complex plant tissues.
5.2 MATERIALS REQUIRED
Permancnl slides of various lypcs of plant ussucs, compound microsct\pc
.
Observations on Simple Permanent r i ~ u k ~
%
Simple permanent tissucs are generally of rl:mlypcs i\ Parenchyma
ii) C611enchyma iii) Sclercnchyrna.
i) Parenchyma
Place a parenchyma slide preparation under thc micracopc and foucs ii.
Observe closely the structure of the parcnchylna cclls'And make a ncat diagram
, in your observation note book. Record the ~ t m ~ t udetails
d of the tissucs in the
\
s@aceprovided klow:
,
You will find:
i) The cells are circular and isadlawettic
ii) They have Intercellular $paces Figb5.1)
Occurrence
@?
Most of the lower plants are formed of parenchymatous cells. Meristems a&-'
also parenchymatous. Epidermis, cortex, pith, mesophyll of leaves, puIp of
fleshy fruits and embryonic tissues are composed of parenchyma cells. a
Functions
The cells have an active pmtoplast. Parenchyma ceUs have functions of
photosynthesis, storage of food material, secretion and exc~tion.T3ey occur as
a pan of xylem and phloem and conduct water and nutrients in solution.
In leaves, parenchyma cells have chloroplasts in them, hence cdled
chlorenchyma. In aquatic plants, they acquire large air spaces to enable the
plants ,to float in water, hence called aerenchyma cells.
ii) Collenchyma
Observe a permanent preparation of collenchyma tissue under a microscope.
Make a neat sketch of the ceUs in your observation notc book. Record the
details of the spcture in the space pr6vidd below!
Study of Plant Tksues
..................................................................................................
You will rmd ~hal:
a) Collenchyma cells are circular and isodiarnetric. Some of the cells may also
bc polygonal in shape.
b) The cell wall is thick, more so in comers of the cells. Therefore, there are
no inlercellular spaces. (Fig. 5.2).
Flg. 5.2: Collenchyma
Occurrence
Young stem pct~olcsof leaves, and stalk of flowers, ribbed stems and petioles
as well as the square slcms of cerlain plants have collenchyma cells.
Function
Collenchyma is a mechanical tissue providing strength and elasticity to the stem
and leaves of plants.
iii) Sclerenchyma
Observe a preparation of sclcrenchyma cells under a compound microscope.
1
Make a neat sketch of the tissue as observed in your record note book. Write
down tl'k structural details of sclerenchyma tissues.
Were you provided with slides of more than one type of sclerenchyma cells?
Yes, the size and shape of sclerenchyma cells are variable and atleast two types
could be distinguished.
a) Elongate cells called sclerenchyma fibres (Fig. 5,3).
1
t
b) Short cells cither isodiametric or irregular in shape called sclereids (Fig. 5.4).
4 Make drawings of both types of cells in your notc book. You will find that
1 sclerenchyma fibres are:
i) long cells with pointed needle like ends.
Laboratorv Course-I ii) dead cells with no protoplast in them.
iii) highly thick walled, the thickening due tir a substance called lignin.
Occurrence
Found in cortex, pericycle, xylem and phloem.
Function
Pmvide mechanical strength to plants.
The sclereids are circular or irregular shaped cells with lignified cell walls.
Lumen
Fig. 5.3: Sclerenchyrpa fibres
The sclereids are also dead cells wilh no protoplast in them.
Occurrence
Found in cortex, phloem, pith, secd coats and fruit wall.
Function
Provide mechanical strength to plant parts.
Fig. 5.4: Sclereids
5.4 OBSERVATIONS ON COMPLEX PERMANENT
TISSUES
Complex tissucs, you have learnt carlicr, arc composcd of diffcrcnt types of ccll
elcmcnts. These dirfercnl cellular clcments form an integral part of a structure
of plant, and carry out a specific function. By way of analogy with animal
tissues, you may recall that blood is a complex tissuc formed of dirrercnl typcs
of cellular elements. Anlong pIants xylcm and phlocm are cxamplcs of conlplcx
tissues. These tissues arc conccrncd w i h transpon of water and nulricnts in
plants, hencc called vascular Lissucs. The vascular tissucs pcrrotm a function
similar to the ones pcrfomcd by thc blood vascular system in animals.
5.4.1. Xylem Study d Plant TLssues
Xylem is a complex tissue forming a part of vascular bundle. It's major
function is conduction of water and solutes. It also provides mechanical
support to plants. As a complex tissue it consists of different types of cells
and elements. The tissues which go to form xylem are a) tracheids b) vessels
c) xylem fibres and d) xylem parenchyma. Place a permanent slide preparation
of xylem undcr a microscope and observe the various elements:
a) Tracheids (Fig. 5.5)
A tracheid is a much elogate cell. The cells are devoid of any protoplast, hence
they are dead cells. The trachcids have a lumen without any contents in them.
The walls of tracheids arc thicker and lignified. Depending on the type of
thickness, tracheids are classificd into annular (ring like thickenings), spiral,
reticulate (the walls present a network like appearance), scalarifom (ladder like)
and pitted (with holes).
b) Vessels
These are long tube like bodies which conduct water and solutes. A trachea is a
vessel formed from a row of cylinderical cells arranged in longitudinal series.
The partition walls between the, cells are perforated so that the entire Structure
is a long continuous vcssel.
c) Xylem Fibres
These are the dead cells which provide mechanical support to the plant. They
are-long cells with lignified walls.
d) Xylem Parenchyma (Fig. 5.5)
These a're the only 11\ Ing cornponcnt of the xylcm of most plants. Parenchyma
is abundant in the secondary xylcm of most plants. The cells may be tlzin
walled or thick wallcd. The cclls have a storagc function, mostly starch and
. fatty substances arc storcd.
I:ig 5.5: Xylem tissue a) traclleld b) parenchyma
Laboratory Course-I 5.4.2 Phloem
Obscrvc a pc -., 'icnl slidc prxt''rallon or ph'ocm undcr ~ h cmicroscnpc. A
phlocm is a , , i l i l ' ~ xlissuc ii. r:l
f l ~ l i n four ~Icmcnts.a ) ~ I C V Cclcmcnts
b) companion . i.1 ,\ .r, I.:, .r11:1 [I ' * - >.
a) Sieve elements IFig. 5.;)
Thcsc arc the mot importa111 I ~ r cnts
lL of phloem. Sicvc elcmcnls consisl of
sieve tubes. Sieve lubcs arc cc' wged in a longitudinal scrics wilh
perforations in the cell wall, call , e plate. Therefore, in the sieve plate
\
cytoplasmic conncctions arc establ~shedbetween neighbouring cclls. The
cytoplasmic conncctions as called plasmodcsmata. The sieve plate is formed by
the primary cell walls of two adjaccnt cells with a middle lamella between
them. Sieve Lubcs have conducting iunction.
Phloem Parenchyma
.;.
./
Fig. 5.6: Phloem tissue
b) Companion Cells (Fig. 5.6)
Companion cells as their name suggests are closely associated with sieve tubes
of flowering plants both during development as well as during functioning.
They are small elongate cells with dense cytoplasm and prominent nuclei. They
occur on the lateral walls of sieve tubes. Companion cells accompanying a
sieve tube may be a single cell of equal length or a mother cell may be divided
transversely forming a series of companion cells. Sieve tubes and companion
cells originate from the same mother cell. The companion cells function as long
as sieve tubes are functional. The companion cells are firmly attached to sieve
tubes.
c) Phloem Parenchyma (Fig. 5.6)
These living cells are also associated ,with sieve elements. They are living cells
with protoplast i n them. They are concerned with storage of organic food
materials.
d) phloem Fibres
These are sclerenchymatous cells. These are dead elogated cells with lignified
walls having single pits. The fibres are of commercial importance as they are
used for the manufacture of ropes and cords.
4
