-
Tnn Fr-,owsn
----'1
r-r Svllabus z Flawer : Stnlctureof a bisexualflower, functions of variousparts'
I
t whorls
of
a
bisexual
and
non-essential
flowers.
Essential
incomplete
to
complete
and
1
introduction
e
Utief
i
and
of
concepts.
Inflorescence
help
enhance
clarity
or
actual
specimens
parts
functions.
Use
of
charts
n"riou,
and
,n"i.
no*"r,
I
I|
I placentation(typesare not requiredin both cases)
----J
L_-
projecting out and each usually ending in a
bilobed tip. These are stamens (collectively
named androecium). Each stamen consists of
threadlike filament and bilobed anther.
Ybu have already learnt that reproduction is the
most important function of any living organism for
the survival of the species.In flowering plants this
function is performed by the flower. The flower is
usually the most beautiful and conspicuouspart of a
plant.
4. Fourth whorl (female parts) ( ? = symbol for
female) (centrally located pistil that may be
formed of a single female unit (carpel) or of several
fused carpels (collectively called gynyecium).
Each carpel consists of a basal ovary, a middle
style and an uppermoststigma.
6.1 STRUCTURE OF A BISEXUAL FLOWER
(FIG 6.1)
shoot in which the haves arc
Ftower fu a specialized.
modifutl into flaral structures.
6.1.1COMPLETE AND INCOMPLETE FLOWERS:
A complete (or perfect) flower is one which
contains all the four types of floral structures. If
one or more sets of floral structures are missing,
the flower is called incomplete (or imperfect).
First of all, there is the stalk (pedicel) which
supports the flower. Some flowers may be without
stalk (sessile). The tip of the flower stalk may be
expanded to form a cup-shapedreceptacle.
The floral parts are borne on the thalamus in
four whorls.
1. First whorl - green sepals (collectively called
Essential (reproductive)and non-essential (nonreproductive) parts of a flower. The essentialparts
of a flower are those that are directly concerned
with reproduction. These parts consist of the
stamens(male parts) and the carpels (female parts).
calyx).
2. Second whorl - large brightly coloured petals
(collectively called corolla).
T1nenon-essential (accessory)parts are simply
the helping partswhich either protect the reproductive
parts of the flower or make the flower attractive for
pollination. Theseparts include the sepalsand petals.
In somecasesthe petals and sepalsare undifferentiated
(togethercalled perianth). When the perianthis non- sTYlEltr
@
greenit is describedas petaloid.
3. Third whorl (male parts) (d = symbol for male)
long thread-like processes somewhat
:-'"*l
z-
J
UJI ANTHER
n
'"'r E l
E
I
fl lrtunuenr
(4)
ovAHY
I
ovuLEl
PETAL
(2)
SEPAL
(1)
When the perianth becomes green like the
sepals,it is described as sepaloid perianth.
Bracts-\When a flower arises in the axil of a
leaf-like structure.this stnrcture is known as bract.
Bracts ma)'h _sreenlike ordinary'leavesor at times
thel'are coloured- The large and colourful bract of
RECEPTACLE
STALK
Fig. 6.1 Generalizedarrangementof parts of a bisexualflower
42
Bougainvillea (Fig 6.2) is easily mistaken for petal.
The actual flower in this case is small, somewhat
cvlindrical and attachedon the inner side of the bract.
Neuter flower - A flower in which both maie
and female reproductive organs are lacking . Lt nnple:
Ray florets of sunflower.
GENERAL DESCRIPTIONOF THE FLOR\L
PARTS
(a) Calyx (sepals).Usually there are five sepai..
Sometimesthey may be less or in a few caseseten
more: The sepalsmay be free (polysepalous) or fusai
(gamosepalous)(Fig 6.4). Sometimes,as in Hibi s cus
(shoe-flower) there may be a secondseriesof sepals
called episepals,collectively called epicalyx. When
the flower opens the sepalsmay fall off or persist.
Sepalsare usually green but in some casesthey are
brightly coloured (called petaloid) as in Gul Mohur
(flame of the forest) where they are red.
6.2
I
frrI
n a
'ely
iof
for
'be
eral
m).
ldle
Large,colouredbracts
Fig.6.2 Bougainvillea.
bear the flowers
Nectaries : Most flowers produce a sweet
fragrant liquid called nectar. Groups of nectarsecretingcells, nectaries are situated usually at the
base of the pistil or on the basesof the petals. The
nectar attracts insects like honeybees, for cross
pollination. In some cases nectaries are very
prominent as in Nasturtium (Fig 6.3)
XVU
(a)
Polysepalous
(b)
(c)
Gamosepalous
Fig. 6.4 Calyx- free (a) and fused (b and c) types of sepals
RS:
The sepalsprotect the young flower bud and
when green they also perforrn photosynthesis.
ich
If
tr8'
Fig. 6.3 Nasturtium.A flower cut mediallyto show the nectary
containinga clear liquid (the nectar)at the bottom
)nrts
red
he
s).
plv
ive
for
ils.
tsd
)nhe
a
rt.
es
rf
6.I.2
SEXUALITY IN FLOWERS
Male. female and bisexual flowers. The anthers
the
stamensproduce pollen which forms the male
of
cells (male gametes).The ovary of the carpel bears
the ovule which encloses the egg cell (female
gamete). The stamens and the carpels are the male
and female parts of the flower respectively.
- A flower which containsboth stamensand carpels
is called bisexual or hermaphrodite or just a
perfect flower.
- A flower which hasonly one of theseparts,that is,
having only the stamens or only the carpels is
called unisexual or imperfect flower, e.g. papaya
. and palm.
- A unisexualflower which containsonly the stamens
is called the male or staminate flower.
- A flower which contains only the carpels is called
the female or the pistillate flower.
(b) Corolla (petals). The petals are generally
arrangedin a single whorl but sometimesthere may
be a double whorl (e.g. Poppy) or in a spiral (e.9.
Water lily). They may be free (polypetalous) or united
(gamopetalous) forming a tube (Fig. 6.5).
Fig. 6.5 Kinds of corolla.A-Free petals,B-Petals fused in a
tubulariorm C-Petals fused,somewhatfunnelshaped
The petals attract insects for pollination. They
also protect stamens and pistils especially when
the petals form a tube.
(c) Androecium (stamens). The number of
stamensin different flowers may vary from a few to
a large number.Each stamenhas two regions: a long
frlament and an anther attachedto its extremit-v.The
antheris usually two lobed. Each lobe has two pollen
sacs (four sacs in all). Within the pollen sacs are
contained pollen grains. When fully matured the
polien sacs rupture to liberate pollen grains. The
pollen grains are generally powdery particles of
different shapesand sizes(Fig. 6.68).
Stigma is the terminal knob-like part, it may be
divided into two or more lobes and may assume a
feathery appearance.The stigma is coveredwith hair
or with glandular papillae. It serves as the landing
place for pollen during pollination.
POLLEN SAC
POLLEN
GRAINS
Style is the tubular slender stalk which connects
the stigma to the ovary.
FllAMENT
Fig. 6.nA-Poiien sacs conta!npolleirgrains(diagrammatic).
B-eclien grainsfrcm differentplantsshow different
shapesand sizes
In androecium, stamens may be free
(polyandrous)as in Petunia, or joined in different
wavs in single, double or several groups(Fig. 6.7):
Monadelphous
(Single group)
(d) Gynoecium (carpels).Gynoecium is also
known as pistil. It is composed of one or more
carpels.Each carpel consistsof three parts-stigma,
style and ovary.
Diadelphous
(Two groups)
Polyadelphous
(Severalgroups)
Fig. 6.7 Cohesion (joining; of stamens.
ti) \Ionadelphous : Stamensare united in one
group by their filaments. Only anthersare free.
e.g., china rose (staminaltube),cotton.
Ovary is the swollen basalportion composedof
oneor many carpels.The inner cavity of the ovary may
be a single chamberor divided into severalchambers
(locules)eachcontaininga numberof roundedbodies,
the ovules.The cushionor swollen region in the ovary
giving origin to ovules is called placenta.
Sexuality in plants
In most plants the flowers are bisexual. They have both
male and femaleparts.
In many plantsthe male and femaleflowers are separate.
Such plants are of two types :
(i) Monoeciousplants(mono: one,oecium:house):Male
and femaleflowers grow on the sameplant ag. muze,
cucumber,pumpkin, etc.
(ii) Dioeciousplants (di : two): Male flower (staminate)
andfemaleflower (pistillate)grow on differentplants
e.g. palm, papaya,etc.
fri
Lil
l'
tiit Diadelphous : The filaments are united in two
bundles.e.g. pea(out of ten, nine stamensform
a staminaltube while one is free).
(iii) Potl adelphous : The filaments are united in
severaigroups. e.g. Bombax.
Hon' to rernember the atlove three terms ?
' Mono -, Di - and Poly - respectively mean single,
two and several.
, Adelphou,sliterally means "group of brothers", here
referring to the part from which the anthers grow out
in bundles. Thus the bundle of anthers arising from a
single part (monadelphousor monodelphous),the
bundles from two parts (diadelphous) and from
several parts (polyadelphous).
6.3
PROGRE'SSCHECK
Mention if the following statements are true (T) or
false (F)
(i) Flowers can be complete or incomplete.
T/F
(ii) A flower typically has six floral whorls.
TlF
(iit
Bracts are usually green, but sometimes large and
colourfirl.
T/F
(iv) Nasturtium has nectaries.
TIF
(v) Stamens and carpels are the male and female
parts
TlF
(vi) The pref,x "gamo-" is used whenever any of the
floral whorls are fused
T/F
(vii) Stigma may be simple or divided into two or more
lobes.
TE
(viii) Papaya is monoecious plant.
T/F
INFLORESCENCF \\D
PI \CE\TATION
Inflorescence is the mode oJ arrangement of
flowers on the axis of the plant
Y
l
-
The flowers may grow in severaldifferent ways
in the different plants such as:
growing out from the axils of
different leaves reaching the
same level making a cluster
I,
$
e
a
r
v)
f
{
4
-
singly either at the apex of the
main stem or at the terminal
apex of the lateral branches,
-
The axis is laterally flattered
making a disc as in sunflower.
The youngest flowers are in
the centre and oldest in the
pesiphery
in the axils of the leaves.
Placentatiorzis the manner in which the ovules
are iuranged in the plant ovary.
Ovules turn into seeds in the mature fruit
(transformedovary). Their differen arrangementscan
be seenin fruits such as thoseof pea,tomato, mango.
lotus. etc.
S
t
POINTS TO REMEMBER
Y Flower is a reproductiveorgan.
Y Essentialparts of a flower include the stamens(malc parts) and the carpels (femaleparts),
Y Sepalsprotect the bud, petals attract insects,stamensproduce pollen grains, carpel receivespollen und its
ovary becomesthe fruit containing seeds(ovulcs).
Y Essentialparts of a flower are the reproductivepar* (stamensand carpels)and non-essentialonesthe nonreproductiveparts @etalsand sepals).
Y Nectaries are cornmon in most brtgh@ colnured (insect-pollinated)flawerc.
Y Sepalsmay be brightly colaured, these are then callcd petnlnids.
Y The pollen grains are generallypowderyparticles of dffirent shapes.
REVIEW QUESTIONS
C. SFIORTANSWER TYPE
A . MUI,TTPLE CHOICE TYPE
l. Explain the following terms :
(a) Incomplete flower
(b) Staminate flower
(c) Pistillate flower
(d) Bisexual ffower
1 . Bougainvillea flower is an example of
(a) an incomplete flower
(b) having a large nectary
2 . Distinguish between the following pairs :
(c) water pollination
(d) large colourful bracts
(a) Flower and inflorescence,
(b) Petals and petaloids.
B . VERY SHORT ANSWER TYPE
t .
Where are the following structures/partslocated and
what are their functions ?
(a) Placenta
(b) Thalamus
(c) Anther
(d) Stigma
Match the parts in Column A with the flowers or
parts of flower in Column B.
Column A
(a) Polyadelphous
(b) Pollen grains
(c) Free petals
(d) Non-essential
(e) Sweet fragrant fluid
Column B
(i)
(ii)
(iii)
(iv)
Polypetalous
4. Why are the following described as stated :
(a) Maize plant as monoecious
(b) Ray florets of sunflower as neuters
(c) Salvia sepals as petaloid
(d) China rose stamens as epipetaloid
Calyx, corolla
Nectar
Bombax
(v) Pollen sac
45
3. Given below are two figures (A & B) of a certain
part of a flower. Study the figures carefully and
answer the following questions:
R. LONG ANSWER TYPE
1. List the four conditions of androecium in flowers.
Which category of these will you assign for China
rose, Bombax, and pea.
E. STRUCTURED/APPLICATIONISKILL
TYPE
1. There is a flower in which you use the following
names : Standard, wings and keel.
(a) Name the flower
(b) What do the namesgiven above refer to ?
-
The figure given alongside
represents generalised
arrangementof the different
parts cf a bisexual flower.
Name the parts numbered
1-10.
(b) Are the contents of the pollen sacs in B male
or female ?
(c) Can you guess how the contents of the pollen
sacs would come out ?
1l\
T/^*"'
ffi
5r
I
POLLEN
GRAINS
' If
z)
4
(a) Which major organ of a flower does the figure
A represent ? What is the collective name of
such organs ?
porrerusnc/
tj J/
8
I
jl.J,'w
10
46
i
ain
I
ure
I
rnd
I
Por,rrNnuoN ANDFnnrn rzATroN
of
len
: self and cross-pollination.
1 Syllabus.' Pollination
t"rtilization.
i
and disadvannges of self and cross-pollirwtion, agents of pollitntion and the characturtsfic feaures of
1 Exnlanation, advantages
pollinated
by
various
egents to be discussed.
llowers
1
i Events taking place between pollfuation and fertilization should be discussed up to fusion of male gamete with egg cell in the
t,
embryo sac. Sndents should be familiar with the terms double fertilization and triple fusion. Fruit and. Seed (definition) and
I significance of Fruit and Seed..
7.I
POLLINATION
What is pollination ? You have read that the
stamensof a flower are the male organs.The anthers
of the stamens produce powdery material called
pollen which consists of particles called pollen
grains. Each pollen grain contains nuclei that
participatein reproduction.For initiating this process
of formation of fruit and seedsthe first step is that
the pollen grains must reach the stigma. It may
happen in three principal ways (Fig. 7.1).
l. The pollen of the same flower may fall on its
stigma by itself (autogamy) (auto : self, gamy:
marriage).
2. The pollen of another Jlower of the sameplant
may fall on the stigma (geitonogamy) (geitono:
neighbouring).
3. The pollen of a flower of another plant of the
same speciesmay fall on the stigma (allogamy)
(allo : other). This transferencecan occur through
wind, insects, or other agentsand the term used
for this transferenceis cross pollination.
flowers of a particular plant may receive all kinds of
pollen----ofits own kind aswell asof others.Similarly,
1. nurocamY (Sameflower)
PLANTA
,
a
f
.."
l
Ar.\.
*-;.'-$*"
Pollination is the process of transference of
pollen grains from the anther to the stigma.
Pollination must occur between plants of the
samespecies.Many differentkinds of flowering plants
may be growing in the samevicinity. For example,an
orchard may have trees of mango, guava, litchi, etc.,
and even some wild trees like neem, jamun or
sheeshammay alsobe growing in the neighbourhood.
Similarly, various crops may be growing in
neighbouring agricultural fields-wheat, mustard,
pulses,vegetablesand so on. The wind may blow away
the pollen from all such plants together and thus the
47
PLANT B
representationof self anc
Fig. 7.1 Diagrannmatic
cross-pollination.
insectslike bees and butterflies generally do not
discriminatebetweenplantsand collect nectarfrom all
kinds of flowers.In theprocess,theinsectsarecarrying
different fypesof pollen on theirbodies.Therefore,the
stigmaof a flower of any one particular plant receives
pollen of its own speciesas well as of others. But
Naturehasso designedthat only the pollen of the same
speciesof plant will survive and grow further to
continuethe processesfor reproductionand the rest of
the types of pollen will fail to germinateand perish.
liinr:is of pollination. There are two kinds
of pollination : self-pollinationand cross-pollination.
7.1.1 SELF.POLLINATION
Self-pollination is the transferof pollen from the
antherto the stigma of the same flower (autogamy),
or to the stigma of another flower of the same plant
(geitonogamy).Pollination between flowers of the
sameplant is consideredself-pollinationon account
of the common genetic characters-i.e. the general
qualities or featuresof any one plant are the samein
the different flowers borne on it.
In some rare cases,as in pansy, some flowers
growing close to the ground level, do not open at all
(cleistogamy,cleisto: closed),the anthersand stigma
lie close to eachother which mature at the sametime
and self-pollination
is assured.
':'::;:r.|it sslf'-pollinationoccur ?
Self-pollination can occur in bisexual flowers,
i.e. tn flowers having both male and female organs,
or it can also occur in such unisexual flowers where
both male and female flowers are borne on the same
plant. To ensure self-pollination, it is necessarythat
the anther and stigma of a flower must mature at
the same time, or if the flowers are unisexual and
borne on the sameplant then they must also mature
at the same time.
Ai{:'ai:i:,9.sanC disadvantagesof self-pollination.
A. Advantagesof self-pollination
1. It is much suFer in suchbisexualflowers where
stamensand carpels mature at the same time.
2. Parental characters are preserved indefinitely.
3. There is no wastage of pollen grains. Even a
small quantity of pollen will suffice.
4. The flowers need not be large and showy.
5. Scent and nectar need not be produced by
fiowers.
48
All the above advantagesmean great economy
on the part of the plant. A lot of nutrient material
which would otherwise be used in the production of
pollen, nectar, scent and large petals, etc., is saved.
B. Disadvantagesof self-pollination
1. Continued self-pollination, generation after
generation,may lead to weakening of the variety
or the species.The seedsproducedthrough it are
poor in quality and give rise to less vigorous
offspring.
2. T\e weaker or defective charactersof the varieW
or breed cannot be eliminated.
3. It does not yield new varieties. The genetictraits
of the same plant with no change and without
any intermixing are passed on to the next
generation. Thus there is little chance for
improvement in the next generation.
7.1.2 CROSS.POLLINATION
Cross-pollination is the transfer of pollen from
the anthers of flowers of one plant to the stigma
of a flower of another plant. This too has
advantagesand disadvantages.
A. Advantagesof cross-pollination
1. The offspring are healthier.
2. The seedsproduced are abundant and viable.
3. New varieties may be produced by crosspollinating two different varieties of the same
speciesor even two species.
B. Disadvantagesof cross-pollination
1 . The pollination is not always certain because
some pollinating agent is always needed which
may or may not be available at the proper time.
2. The pollen has to be producedin large quantity
to ensure chancesof pollination which means a
lot of wastage of pollen.
3 . The process is uneconomical for the plant
becausethe flowers have to be large, coloured,
scented and have to produce nectar-for
attracting pollinating agents.
The differences betu'eenself-pollination and
cross-pollinationare summssisgdin Table7.1.
\ature far.ours cross-pollination.The vast
majoriry' of flo*.erin_e plants are cross-pollinated.
Some of the various devices (contrivances) or the
omy
erial
)n of
r-xed
Thbte 7.1 : Differences between self-pollination and cross-pollination.
Cross-pollination
l. It is the transfer of pollen grains from the anthers to the
stigma of the same flower (autogamy).
2.
3.
4.
5.
6.
No external agency or agent is required
Male and female parts manre at the same time.
It can occur even when flower is closed.
It preserves parental characters
New variations are impossible, hence young ones cannot
adapt changed environmental conditions.
7. New varieties are not possible
fter
iety
are
ous
efy
conditions which favour cross-pollination are as
follows :
1. Unisexuality. The flowers may be either male or
female and they may be borne on separateplants.
In this way cross-pollination is the only
possibility; e.g.palms and papaya. (Papaya
usually has separatemale and female trees, but
less frequently there may also be a hermaphrodite
tree bearing both kinds of flowers). In cucumber,
gourd, etc., the male and female flowers may be
borne on the sameplant.
lits
out
3Xt
[or
)m
na
AS
).
S-
1e
t
Li€
ch
te.
ty
a
nt
d,
tr
rd
st
d.
rc
I
2. Different timings of maturation of androecium
and gynoecium (DICHOGAMY). In many
bisexual flowers the anthers and stigma of the
same flower mature at different times.
- In some plants anthers of the flower mature
earlier than the stigma (protandry), e.g.
bhindi, sweet pea, salvia, sunflower.
- In some plants, the stigma of the flower
matures earlier than the anthers(protogyny,
protos : first, gyne ; female), e.g. custard
apple, peepal.
It is the transferof pollen grains from the anthersof
one flower to the stigma of anotherflower of a
different plant of the samespecies.(allogamy).
An external agent(wind, water, insect) is always requfued.
Anthers and stigma mature at different times.
It can occur when flower is open.
It does not preserveparentalcharacters.
Offspringsare healthierto adopt envtonmental changes.
New varietiescan be produced.
Fig.7.2. Heterostyly: A-long styledflower B-short styledflower
stigma of the sameflower. For example,a hood
covering the stigma acts as a mechanicalbarrier
in Pansy flowers, Iris, etc.
5. Heterostyly - In such flowers the stigma and
anthers grow at different heights which does
lnot favour self-pollination. e.g. prim rose, oxalis
(Fig. 7.2).
7.I.3 AGENTS OF CROSS.POLLINATION
The two commonest agents of cross-pollination
are insects and wind. But, some flowers are also
pollinated by certain animals and birds, like squirrels,
bats, etc., or even by water in the case of some
aquatic plants. Each category has some special
features to promote chancesof pollination.
In either case, cross-pollination is the only
possibility.
3. Self-sterility. This is a condition in which even
if the stigma receivespollen from the anthersof
the same.flower, the pollen fails to undergo
further growth. In such cases, only the pollen
from different plants of the same species, can
effectively complete the processof setting of the
seedse.g.- Ray florets of sunflower, orchids, etc.
4. Mechanical
or
Structural
barriers
(HERKOGAMY) (herkos : barrier). In some
flowers the pollen of a flower cannot reach the
49
Insect-pollinated (or entomophilous; entomon:
insect, phile : affinity) flowers usually have the
following characteristics:
1. The flowers are large.
2. They are usuallybrightly colouredto attractinsects.
3. They usually emit scentfor attractinginsects.
4. They producenectar which is food for the insects.
5. The pollen grainsaresiic@ or spinyto enablethem
to be carriedby the insectseasily.
6. The stigmais stickyanddoesnot generallyhangout
from the flower.
7. The flowers tend to be in clusters to make them
conspicuous,especially in the cases where
individual flowers are small, e.g. Dahlia.
Wind-pollinated (or anemophilous, anemo :
wind; phile : affinity) flowers usually possessthe
following special features. (Example : Maize)
1. The flog'ers are srrtctll.
2. Thel' are usuall1,rtcttbrigitlv colouredand often
dull green.
\C.entOf nectaf.
3. Thet' ,,, ;.. , lt71.tiiii;g
4. The stamensare 1i,rt<riridltartgr;ut of the flower
to be exposedto n'ind.
ta the
ortd loo.sahattctc'ltad
5. The antherslre r't:.i'?€
filament-sso that the slightest wind may move
them (r'ersatile).
6. Poilen is producedin verv lurge rltnntitie.s.
7. Pollen grains are ligh,t, drv and snnoth so that
thev can easily be canied away by wind.
8. The stigmas are .feathery and lrung out of the
flower to trap the pollen grains.
Fiq. 7"3. Vallisneria show!ng male anr:ffemale plants;
note the free floating rnale ilr:wert.
\\'ater-pollinated (or hydrophilous, hydro :
water, phile : affinity) flowers are found only
in aquatic plants. They have the following
characteristics:
1. Pollen grains are producedin large numbers.
2. In some plants the pollen grains have a specific
gravity almost equal to that of water so that they
remain floating below the surface of water.
3. In some speciaicasesmale flowers are suchthat
they float on the surface of water till they meet
female flowers (Fig. 7.3) e.g. Vallisneria.
very large and are found at ground level. The pollen
grains of one flower get attached to the feet of
elephantsand may be carried to the stigma of another
flower when trampled by those feet.
Artificial pollination. When man himself
transfers pollen to the stigma it is called artificial
pollination. In the ancientcivilization of Babylonia,
it was a common practice to sprinkle "male flowers"
of palms on the "female" flowers; of course, at that
time they neither knew the sexuality of palm flowers
nor anything about pollination.
Some flowers are pollinated by birds
(ornithophily, ornitho; bird), e.g. Bignonia, canna.
In modern times, artificial pollination (also called
Elephophilyis the pollination affectedby eiephants.
crossing) is a standardpractice adoptedby
artificial
Elephophily is found rn Rffiesia whose flowers are
"fable 7.2 : I]ifferences between w'ind-pollinated and insect-pollinateclfiowers
Insechp ollinated Jlow ers
Wnd-pollinated flowers
l.
Flowers are unisexual. dull coloured. without scent and
nectar.
2. Pollen grains are produced in lmge number, some go
waste.
l.
Flowers are brightly coloured, scented and secrete
nectar.
2. Less pollen grains are produced becausethey are
transported mechanically by insects.
3. Pollen grains are small, light and smooth.
4. Stigma long and hangs out of the petals, feathery or sticky
5. Stamens long and protrude above petals.
e.g. Maize, grass, rice, wheat.
50
3. Pollen grains are largel sticky and spiny.
4.
Stigma often deep in corolla and small.
5.
Stamens may be within corolla tube.
e.g China rose, Salvia" pea sunflower
n
piant breedersand scientistsin their efforts to evolve
new varieties. They remove the anthers in young
flowers (emasculation)and cover theseflowers with
plastic bags. Later, they pollinate such flowers with
the pollen from the plants of the desired variety.
:-.2 SfiF,fEHXAMPLES ilF ITOLLINAI'ION
(1) In insect-pollinated sweet pea (Fig. 7.4)
the insectssuchas the bee,alight on the conspicuous
corolla. The bee thrusts its long tongue in searchof
'wing petals' of the flower
nectar.In this struggle,the
'wing petals' along with the 'keel
are depressed.The
petal' are forced down and the stamensand stigma
touch the undersideof the body of the insect. If this
insect has already visited anotherflower it may have
some pollen sticking on its body. The pollen is now
transferred to the stisma of this new flower thus
STANDARD PETAL
affecting pollination. When the insect flies away, it
may, in tum, carry some pollen of this flower to
other similar flowers. However, if cross-pollination
does not take place, there is every chance of selfpollination in this case, since both the stamensand
the carpelsare enclosedwithin the keel and are more
or less at the same level.
(2) In wind-pollinated maize (Fig. 7.5)
pollination is brought about by wind. As the wind
blows, the pollen from the outwardly hanging anthers
(in the tassel) is blown away easily becausethe
anthers are so loosely attachedto the filament that
the slightestwind will shakethem. The pollen blown
away by the wind may fall on the feathery stigmas
of the female flowers which have a large surfacefor
this purpose. The male flowers mature earlier than
the female ones, so that there are less chancesfor
self-pollination.
WING
PETAL
(TASSEL)
KEEL
PETAL
SEPAL
n
I
r
ES (SILK)
STANDARDPETAL
WHOLEFLOWER
m
FEMALE
@}W w"
WINGPETAL
INFLORESCENCE
(coB)
KEELPETAL
STIGMA
E
FLOWER (Petals
removed)
n
STAMENS
STAMINALTUBE
l.
Matchtheitemsin ColumnI with thosein ColumnII
(i)
STIGMA
POLLEN GRAIN
PROGRESSCHECK
l . t
SEPALS FREE STAMEN
"ffi
F i g . 7 . 5 M a i z ep l a n t
(ii)
CARPEL
(iii)
(iv)
Fig. 7"4.Floral parts of sweet pea.
51
Column I
Featherystigma
hangingout
Different timings for
maturationof anthers
and stigma
Pollination by elephant
Flowers producenectar
Column II
Rafflesia
Entomophilous
Wind-pollination
Dichogamy
2. Cornpletethe toltowing ststsrr\euts'.
(i) Pollination is the processof transferenceof
(ii) The two kinds of pollination
are -
Ttre PoIIen Grain
The mature pollen grain (Fig. 7.6 B) is a cell
with a double wall - the outer exine and the inner
intine. Its nucleus has already divided into a tube
nucleus and a generative (male) nucleus. At this
stage,the pollen is transferredto stigma (pollination).
Further changesin pollen grain occur only if it has
fallen on the stigma of a plant of the same species.
and
(iii) For self-pollinationthe flowers neednot be
and showy.
(iv) For self-pollnation
and -
must
mahrre at fhe same time.
(v) Self-pollination does not yield
(vi) In
The Ovule
varieties
Ovule is the inner part of ovary. Ovule is destined
to become seed and the ovary to become fruit
containing the seedinside. There may be
o a single ovule producing single seededfruit, or
. many ovules producing a many-seededfruit.
pollination there is much wastage of
7.3 FERTILIZATION GIG. 7.6)
Fertilisation is the union of male and female
gamete nuclei.
Each ovule has one or two protective coverings,
the integuments.
In flowering plants
o
o
The integuments leave a small opening the
micropyle at one end (for the entry of pollen tube).
The pollen grain carriesthe male gamete.
The ovule inside the ovarv contains the female
gamete.
Enclosed by the integuments is the nucellus (a
mass of food laden cells), and further inside the
nucellus is the embrvo sac.
EXINE
TUBE
NUCLEUS
GENERATIVE
NUCLEUS
GERMPORE
C
TUBENUCLEUS
POLLEN
TUBE
SPERM
NUCLEI
TUBENUCLEUS
CELLS Two fefiilisations (double fertilisation)
MICROPYLE
F i g . 7 . 6 G e r m i n a t i o no f p o l l e n a n d
) - P o l l e n CENTRAL CELL
f e r t i l i z a t i o n( d i a g r a m m a t i c A
grainsgerminatingon stigma,one pollen
tube has entered ovule. B-A mature
SYNERGID
pollen grain, C-Pollen grain beginning
to germinate,D{erminated pollengrain,
EGG CELL
E-Ovule showingthe embryosac in it and
MICROPYLE
the events occurring there.
POLLENTUBE carrying
two sperm nuclei (Tube
nucleushas degenerated)
52
1. Two polarnucleiuniteto formsecondary
nucleusand then one spermnucleus
from the pollentube uniteswith the
' 'secondarynucleus,to form endosperm
ceff. (This is describedas triple fusion,
involving2 polar nucleiand 1 sperm
nucleus,i.e. 3 nucleifusion).(One,
FERTILTSATTON)
2. The otherspermnucleusentersegg cell
throughthe assistanceof synergids
whichthen degenerate,
and uniteswith
its nucleus(SecondFERTILISATION)
INTEGUMENTS
[Can you justify when we say that there is double
fertilisation in flowering plants ?l
ell
ter
be
ris
r).
.as
:S.
ed
rit
ls'
he
(a
D
I
rry
US
rm
)n.
rm
ell
ds
rSl
)
)le
The embryo sac containsseven(3+3+1) cells :
3 cells at micropylar end - one egg cell and two
synergids,
c 3 cells at oppositeend,called antipodal cells, and
o 1 large central cell. The central cell is different
containing two nuclei called polar nuclei.
c
Germination of pollen grain
Pollen grain germinatesonly if it has fallen on
the stigma of the same plant species,otherwise, it
gets decomposed.
Stigma of the flower provides a solution of sugars
to feed the pollen cell. A pollen tube grows out of
the pollen grain by breaking through its exine. The
generativenucleus divides into two nuclei (male
gamete nuclei also called sperm nuclei). Thus there
arethree nuclei which are not separatedby cell walls,
they share a common cytoplasm.
The pollen tube grows through the stigma and
style by dissolving the tissues with the help of
enzymes and reaches the ovary. There, it pushes
through the micropyle and reachesthe embryo sac.
The tube nucleus which had directed the growth
of pollen tube all the way down, now disintegrates.
Now, the pollen tube entersone of the synergids
andreleasesits two spermnuclei. Of these,one sperrn
nucleusentersthe egg cell and fuseswith its nucleus,
while the other sperm nucleus moves towards the
two polar nuclei in the central cell and fuses with
them (thus 3 nuclei together to produce the
endospermnucleus).All togetherthere have occurred
rwo fertilisations.
Double fertilisation
1. One spermnucleusfusedwith egg cell nucleus
,2. The other spermnucleusfuseswith two polar
, nuclei together
i
Fate of floral parts after fertilization. After
t'ertilization the flower has served its purpose.
- The petals, stamens,style and stigma wither
and generally fall off.
- The calyx may either fall off or may remain
intact in a dried and shrivelledform. Apple and guava
show such dried sepals very clearly.
- The ovary enlargesto form fruit, the ovarian
wall forming the fruit wall. The ovary wall may
either form a dry and hard fruit wall or a fleshy fruit
wall.
- Ovules become the seeds.
The fruit contains one or more seedswhich are
developed from one or more ovules attachedto the
ovary by meansof placenta(e).When the fruit is ripe
the seedscontainedinside are releasedby one or the
other method and grow into new plants in suitable
conditions.
The fate of various parts of the ovary after
fertilization during the formation of fruit is asfollows:
P,{RT
WHAT I'I'BECOMES
Ovary
Ovary wall
Owle
Placenta
Outer integument
Inner integument
Secondarynucleus
Egg cell
I
Synergids& J
Antipodal cells
ifl
l . l
-,
Fruit
--)
Pericarp
-)
Seed
-)
Stalk of the seed
-)
Testa
-)
I ^
I Seed coat.
Tegmen J
Endosperm
-)
Embryo
-+
Dis<irganised
-)
PROGIT,ESS
CHECK
Mention if the following statements are true
(i)
Intine is the outer wall of pollen grain.
(ii)
Pollen tube enters ovule through micropyle.
(iii)
Zygote gives rise to embryo.
(iv)
(v)
Ovule becomes fruit.
Dry sepals may persist in some fruit.
POINTS TO REMNMBER
I Self-pollinatinn is surer and it presemesparental characters (same variety), but it leads to weaker generatians.
Y Cross-pollination produces heahhier offspring and new varietics.
Y Plants have evolved several methods to favour cross-pollination.
I Insect-pollinated Jlowers are large, bmghfu coloured, scent and nectar-hearing wilh sticlcy pollen and sticlcy
stigma
7 Wnd-pollinated, tlowers are small, dull nectarless with light and ilry pollen anil feathery stigrna.
Y Pollen grain germinates on stigma and the pollcn tube penetrotes ovule,
Y Aftir fertilizatian mast other Jloral parts dry and fall off while the ovary enlarges to fonn fruit with ovules
becoming seeds.
RS\IE\'{
Q\JEST\ONS
CHOICE TYPE
A. MUAIPLE
1. Which one of the following is one of the
characteristics of self-pollinated flowers ?
(a) Flowers are large and showY
G) Flowers remain closed and do not open
(c) Stigma and anthers mature at the same time
(d) Pollen is produced in very large quantities
2. Exine and intine are the Parts of
(b) Pollen grain
(a) Embryo sac
(d) Seed
(c) Stigma
B. \'ERY SHORT ANSWER TYPE
1. Match the items in Column A with those in
Column B.
Column B
(a) Generative nucleus (i) Pollen tube
(ii) EndosPerm
(b) Germ pore
nucleus
(iii) Testa
(c) Exine
(d) Secondary nucleus (iv) Fertilization
(v) Male nuclei
(e) Integument
(vi) Rough
(0 Egg nucleus
Column A
2 State the name of the chief pollinating agent
against the correspondingplant by choosing from
those given in brackets.
(Crow, butterflies, mosquito).
(a) Dahlia
(Bees, locusts, rain, wind).
(b) Maize
(Wind, water, ants, rabbits).
(c) Vallisneria -
3 . Fill in the blanks with suitable words.
(a) Transference of pollen grains from anthers
to stigma of the same flower is called
(b) Different timings for maturation of
gynoecium and androecium, is called -.
(c)
is a water-pollinated flower.
4 . Name the parts of the ovary which give rise to:
(b) Fruit (a) Seed (c) Fruit wall
Give one word/term for the following :
(a) A flower containing both male and female
parts
(b) Arrangement of flowers on a twig/stem
6. Give the technical terms for the following :
(a) When pollen grains of a flower reach the
stisma of the same flower.
(b) When maturation time of reproductive parts
in a flower is different
(c) When stigma and anthers do not grow up to
same height, which favours only crosspollination ?
(d) Pollination of flowers by insects.
(e) Pollination of flowers by birds.
C. SHORT ANSWBR TYPE
i. Explain the following terms :
(a) Ornithophily.
(b) Elephophily.
(c) Artificial pollination.
2. What happensto the following after fertilization?
(b) Calyx
(a) Ovules
(d) Stamens
(c) Petals
3. Mention any two contrivances in flowers which
favour cross-pollination.
D. LOF{G ANSWER TYPE
L What are the advantagesof the following in the
flower to the plant concerned ?
(a) Long and feathery stigma
(b) Brightly coloured petals
(c) Smooth and light pollen
(d) Protruding and easily movable anthers
(e) Fragrant nectar
2. Describe the advantagesand disadvantagesof
cross-pollination to the plant.
E. STRUCTURED/APPLICATION/SKILL
TYPB
1. What is the function of the pollen tube ? Explain
it with the help of a diagram.
a
2. Given
alongside is
diagrammatic sketch of the
sectional view of a Plant Part
relating to reproduction.
(a) Identify the plant part as a
whole
(b) Name the structural parts
numbered 1-5.
(c) Where would it be found
as a stage as shown ?
(d) What is the function of part 4?
(e) What immediately next happens
to the part 5?
trts
Snpns-
SrnucruRt ANDGnnvuNATIoN
Ito
ss-
r
Slllfuus
-
-
-
,
-
-
-
-
-
-
.
1
: Structure of dicot and monocot seeds. Germination of seeds, types, and conditions for seed germination.
I
,
Conditions I
Maize grain. Differences between hy'pogeal and epigeal germination.
germination
Bean
seed
and
of
and
Structure
,I
I
for seed germi-nation should be dealt with by experiments.
L - -
8.2 CLASSIFICATIONAND STRUCTURE OF
SEEDS
8.1 WHAT IS A SEED ?
)n?
ich
the
of
iln
Before we talk about the germination of seedsit
will be appropriateto refresh your knowledge what
the three terms FRUIT. SEED and GRAIN actuallv
mean.
Tlpes of Seed
Broadly the seeds are of two kinds
monocotyledonous and dicotyledonous.
- Monocotyledonous seedscontain one cotyledon
(seedJeaf)e.g. maize,grasses.
- Dicotyledonousseedscontaintwo cotyledonse.g.
pea, gram, bean.
Fruit is the enlarged ripened
ovary, the ovarian wall forming the
fruit wall enclosing the seed.The
fruit protectsthe seedand helps in
seed dispersal.Examples. Mango,
pea pod.
Seed is the ripened ovule. It contains
embryowhich developsinto anewplant. The
seed coat protects the embryo from
mechanicaldamage.Example: Bean seed,
peas.
Grain as found in maize, wheat, etc, is
actually the fruit in which the fruirwall and
the seed coat are fused together to form a
protective layer.
Seedsvary in size.
- Some are so small that they are barely visible to
the naked eye e.g. poppy seeds,orchid seeds.
- Some are quite large as in watermelon and
pumpkin or even in mango (the stone).
- Largest seedsare those of coconut and double
coconut.
w
The size, shapeand structureof seedsof different
plants vary considerablybut the basic structureof most
seedsis same.
AS:
MORE ABOUT SEED
- It is a mature ovule after fertilisation.
-
It contains a tiny living plant the embryo
(developedfrom the fused spermnucleusand the
egg nucleus).
-
The embryoremainsin an inactive (dormant)state
until exposed to favourable conditions when it
germinates
-
The seed also contains food material for the
nourishmentof the embryo during germination.
-
On the basis of endosperm, seedsare classified
(1) Albuminous (endospermic)cotyledons are
thin and membranous and endosperm persists e.g.
Dicot albuminous seeds : poppy, custard apple.
Monocot albuminous seeds: cereals,millets, palm.
(11)Exalbuminous (non-endospermic)- In such
seeds,the cotyledon stores food and becomesthick
andfleshy e.g.Dicot exalbuminousseeds- Gram,pea,
mango, mustard and Monocot exalbuminousseedsVallisneria, orchids, amorphophallus.
1. TIm BEAN SEED(Fig.8.1)
There are a number of different kinds of beans
such as broad bean, lima bean, french bean, etc., but
the generalstructureof their seedsis the same.Most
are kidney-shapedwith a convex and a concaveside.
The embryo can withstand unfavourable
conditions of temperature, drought, etc. (Some
seedsare known to remain dormant even up to
100 yearsor more).
55
RADICLE
COTYLEDON
A
B
WITHTWO
PLUMULE
LEAVES
RUDIMENTARY
EPICOTYL
TEGMEN
TESTA
HYPOCOTYL
RADICLE
V
COTYLEDON D
Fig.8.1 Structureof Beanseed. A & B-External structure,
C-Testa removed, D-Seed cut open to show various parts.
Seed coat or the testa is the outermost hard
brownish covering. It protectsthe delicateinner parts
ofthe seedfrom injury and from the attackofbacteria,
fungi and insects.
Tegmen (Fig. S.1 D) is a thin inner layer lying
next to the testa,and this also is protective.
Hilum is a distinct whitish oval scar on the
concaveside of the seed.It representsthe spot where
the ovule (now the seed) was attachedto the ovary
wall through placenta.
A tiny pore micropyle is situated close to the
hilum. It marks the openingthrough which the pollen
tube had entered the ovule. Micropyle servestwo
functions :(1) When soakedin water the seedsabsorbit mainly
through this micropyle and make it available to
the embryo for germination.
(2) It provides for the diffusion of respiratory gases
for the growing embryo.
Below the seed-coatare two thick cotyledons
which contain food for the embryo and protect it'
On carefully separatingthe two cotyledonsthe tiny
embryo can easily be seen attachedto one of the
cotyledons. The embryo consists of two parts-the
radicle which later forms the root and the plumule
which later forms the shoot.The plumule consistsof
a short stem with a pair of tiny leavesand a growing
point betweenthem.
(Do not misspell radicle as "radical" which is a
term in chemistry.If you do so,you may lose marks in
the examination)
2. MAIZE GRAIN (Fig. 8.2)
The maize grain is actually fruit in which thefruit
wall and the seed-coatare fused together to form a
protective layer. Therefore, we call such a fruit as
grain.
On one side of the grain occurs a small lightcoloured oval area which marks the location of the
embryo inside. The rernainingmajor part of the grain
contains a large endospermwhich is rich in starch.
The endospermand the embryonic part are separated
from each other by a thin epithelial layer. The
outermost layer of the endospermis rich in protein
and is called aleurone layer.
The embryo consistsof a single cotyledon (here
calledscutellum), aradicle and aplumule. The radicle
is towards the pointed end and it is enclosedin a
protective sheath,the coleorhiza. The plumule is
towardsthe upperbroadersideof the embryonicregion
and is enclosedin a protective sheath,the coleoptile.
POSITIONOF
PLUMULE
SCUTELLUM
FEATURES
EXTERNAL
ALEURONELAYER
ENDOSPERM
EPITHELIUM
SCUTELLUM
(cowLEDoN)
coueoerrr-lE
eLUMULE
Ia
lR
RAD|oLE
lv
coLEoRHlzA__j6
L O N G I T U D I N ASLE C T I O N
t r i c , 3 . 2l t a z e g r a i n
56
a
in
it
a
IS
tte
Jl
[.
rd
re
n
:e
te
a
ts
,n
COI{DITIONS I\ECESSARY FOR GERMINATION
The maize grain'is monoeotyledonousand
endospermic.Someotherexamplesof this type of
grain arerice, wheatandoat.
Water, suitable temperature and air (oxygen) are
necessaryfor germination.
1.Water : The seed obtains water from its
environment,i.e. from the soil, in natural conditions.
The water is absorbedall over the surfacebut mainly
through the micropyle. Two main usesof water are:
(i) The seed swells and consequentlythe seedcoat rupturesallowing the elongatingradicle to come
out and form the root system.
(ii) Water is necessaryfor chemical reaction and
for the enzymes to act upon the food stored in the
cotyledons or endosperrnso that it may convert into
a diffusable form dissolved and utilized bv the
growing embryo.
MAJOR DIFFERENCES BETWEEN BEAN SEED
AIVDMAIZE GRAIN
BEAN
ry
M'ArzF.@
Ttwo cotyledons.
No endosperm.
Large embryo.
Plumule leaves
folded.
5. Plumule large.
6. Hilum and micropyle
visible.
7. Seed separately
containedin the fruit
called pod.
l.
2.
3.
4.
r
One cotyledon (scutellum)
Large endospermpresent.
Small embryo.
Plumule leaves rolled.
Plumule very small.
Hilum and micropyle not visible.
The seed wall and the fruit wall
fused to form a single grain with
no separateseed.
2. Suitable temperature : Both very low and
very high temperatures are unsuitable for
germination. A very low temperatureinhibits the
growth of the embryo and a very high temperature
destroys its delicate tissues. A moderately warm
temperature(25"C to 35'C) is usuallyfavourablefor
germination and it is also called optimum
temperature. Seedsof tropical plants often need a
higher temperaturefor germination than those of the
temperateregions.
PROGNESSCHECK
areTFue(T) or
l . Mentionwhetherthe following statements
False (F)
(i) Plumuleis the future root and radicle the future shootof
the plant.
(T/F)
(ii) Micropyle servesfor the eme-rgence
of the radicle. (TiF)
(iii) Cotyledons in castor are a big store of food for the
embryo.
(iv) Maizegainhasa largeendosperm.
(v) Tegmen
coatin beanseed.
is theoutermost
(T/F)
(T/F)
(T/F)
8.3 GERMINATION
The seedcontains a dormant embryo.In a dry
seedthe embryo is inactive. It is said to be in a state
of dormancy (a period of rest.) Outwardly,it appears
to be without life. but in fact all the chemicalactivities
of life are going on in it although they are very slow
and little food is utilized. The dry seedsconsume
oxygenandgive out carbondioxide, both in exffemely
minute quantities,and they releasesomeheat as well.
When placed under proper conditions the dormant
embryo awakens,i.e. it becomesactive and starts
growing into a seedling.All the changesleading to
the formation of a seedling are collectively called
germination. Germination is the formation of a
seedling developed from the embryo.
A fresh seed from a plant normally does not
germinateeven if the conditions for germination are
favourable.It must passthrough a period of dormancy
during which it undergoesphysiological maturation.
) l
3. Oxygen : During germination there is rapid
cell division and cell growth for which energy is
required.This energy is availableonly by respiration
(oxidation of food) and hence the need for oxygen
(or air).
Seedssown yery deepin soil fail to germinate
Two main reesons :
1. No propersupply of oxygen(for rqspiration)
2. Insufficient pushing force in the emtryonic parts
(hypocotyl or epicotyl) to break through the upper
laversof soil.
8.4 SOME BXPERIMENTS ON GERMINATION
1. Experimentto prove that water is necessaryfor
germination.
Take two beakers and mark them A and B. In
beakerAplace someseedsof greengram (or pea,etc.)
on wet cotton wool. In beaker B place some similar
seedson dry cotton wool. Keep both the beakersin
an ordinary room. In a day or two, the seedsin beaker
A will germinate but not in beaker B, showing that
water is necessaryfor germination.
2. Experimentto prove that a suitabletemperatureis
necessaryfor germination.
Take two beakers and name them A and B. Place
somegreen gram seedson wet cottonwool in eachof
the two beakers. Keep beaker A in an ordinary room
and beaker B in a refrigerator. In a day or two, the
seeds in beaker A will germinate, showing the
importanceof a suitabletemperanre for germination.
The seedsin beaker B may not show signs of
germination, or may germinate after several days
though not to the extent the seeds in beaker A
germinate.
3. Erperimentto provethat air (oxygen)is necessary
for germination(Fig. 8.3).
Take two conical flasks. Name them A and B.
Spreadwet cottonwool in each flask and place on it
some soaked gram seeds. Lower a small test-tube
containing alkaline pyrogallic acid, which absorbs
oxygen, in flask B by meansof a thread,taking care
that not a singledrop of the chemicalfalls on the seeds,
or the coffon-wool. Keep the tube hanging by fixing a
cork on the mouth of the flask. Arrange flask A in the
same way, except that the test-tube in this flask
containsplain water.Placethe two flasks in an ordinary
room. The seedsin flask A will germinate showing
the importanceof oxygen for germination.The seeds
in flask B do not germinatebecausethereis no oxygen
(theremay at the most be very slight germinationdue
to anaerobicrespiration in the absenceof oxygen).
Fig. 8.3 Seedsrequireair (oxygen)for germination.
A-Seeds germinatein ordinaryair,
B-Seeds do not germinatein air without oxygen
4.
bottom one is deep in water. The experimental
set-up is left in a warm place for a few days and the
result is as follows :- The middle seed germinates.It getsboth oxygen
and water.
- The top seeddoesnot germinate at all. It gets only
oxygen but no water.
- The bottom seed does not germinate or stops
germinating afterthe emergenceof a small radicleIt gets water but very little oxygen (from the air
dissolved in water)
The experimentconclusively proves that water is
essential for germination, but the other requirement
of oxygen is not fully demonstrated.
Fig. 8.4The three-beanexperimentto demonstrategermination
8.5 TYPES OF GERMINATION
The region of the axis between the point of
attachmentof cotyledons and the plumule is called
epicotyl. The region of the axis below the cotyledons
is called hypocotyl. Both the epicotyl and hypocotyl
of a seednever elongatetogetherduring germination.
It is either the epicotyl or the hypocotyl that elongates.
If the epicotyl elongates,the cotyledons remain
underground(or on the ground if the seedis just on
the ground) and the germination is then called
hypogeal e.g. pea and gram. If the hypocotyl
elongates,the cotyledonsarepushedabovethe ground
and this type of germination is called epigeal (e.9.
castor,bean, etc.).
HYPOGEAL
GERMINATION
The three-bean seeds experiment (Fig. 8.4).
In this experiment three mature air dried
bean seeds are taken and tied to a glass slide at
three positions as shown in the figure. This
slide is kept in a beaker containing water in a
manner that the top seed is well above water,
the middle one is just at the water level and the
l
Cotyledons remain
underground.
2. Epicotyl elongates.
EPIGEAL
GERMINATION
1 . Cotyledonspushed
abovethe ground.
2. Hypocotyl elongates.
A method to observestagesof germination. Put
sterilized sand in a glass vesselin which filter paper
56
rtal
the
gen
nly
)ps
rle.
air
ris
ent
or ordinary white paper is lined beside the inner wall,
and place seedsin between the paper and the glass.
When water is added to the sand in the vessel, seeds
will absorb the water and germinate in a few days.
8.6 GERMINATION IN SOME COMMON SEEDS
Pea seed(Fig. 8.5) (Hypogeal) : The seedabsorbs
water and swells considerably. The testa softens and
bursts. The radicle emerges,grows downwards and
forms the root system. The plumule grows upwards
andfonns the shootof the seedling.In the earlier stages
of development, the plumule is arched and thus
protects the young shoot from injury during its
emergencefrom the soil. The cotyledons supply food
till the seedling is able to exist independently. Later
they wither and shrivel up. The cotyledons remain
underground and germination is hypogeal (hypo :
below + geo.' earth).
soil. Germination is, therefore,epigeal (epi : above;
geo : eafih). The cotyledons become the first green
leaves and soon fall off after the foliage leaves grow.
Maize grain (Fig. 8.7) (Hypogeal) : The grain
imbibes water and swells considerably.The radicle
pierces through the protective root sheath(coleorhiza)
and the fruit wall and grows downwards to form the
root system,but it dies off soon. New roots develop
from the baseof the stem (adventitiousroots).
ROOT
FIBROUS
Fig.8.7 Germinationof maize.Hypocotyldoes not
elongate(Hypogeal)
ion
of
.ed
)ns
ryl
)n.
es.
rin
on
ed
yl
nd
,8.
Fig. 8.5 Germinationof pea. A-Seed (outer view),
B-Seed showing emergenceof radicle, C-Stages of
germinationin soil ; note that the cotyledonsremain
underground(hypogeal)
Bean seed(Fig.8.6) (Epigeal) : The seedabsorbs
water and swells. The radicle grows downwards to
form the root system.The archedhypocotyl grows and
becomesstraight, bringing the cotyledons above the
The plumule pierces through its protective sheath,
coleoptile, and grows straight upwards. The two
protective sheaths,coleorhiza and coleoptile, may be
seen as a membranous covering on the axis of the
seedling.
The cotyledon (scutellum) absorbsfood from the
endospermtill it is exhausted.The hypocotyl doesnot
elongate.Germination is hypogeal.
Viviparous germination - (a specialtype) - The
mangrove plants Iike Rhizophora (Fig. 8.8) and
Sonneratia,show a specialmode of seedgermination
HYPOCOTYL
HYPOCOTYL
ut
er
Fig.8.6Germinationof bean.Hypocotyl(regionbelowcotyledon)
elongatesto push the cotyledonsup abovethe ground(Epigeal)
tr,tUO--j
Fig. 8.8 Vivipary.A-Twig ol Rhizophorashowing viviparous
germination;B-Seedling growingin mud,
calledvivipary in which seedgerminates inside the
fruit while it is still attachetl to the parent plant
After germination, the plant drops the seedling into
the soil rvhich develops root and fixes itself.
(Wviparous: producinglive young ones)
riFl
(i)
state
In a dry seedthe embryo is in ...........................
(active/quiescent)
TIIE SEEDLING
Germination in any plant endswith the formation
of a seedling.
Seerilingis a stageof the growth of a plant from a
seedbeforei: hasbecomewholly independentof the
tbod stored;n it.
(ii)
Water is absorbed by the seed mainly through
.. (entire surface/micropyle)
PROGRESSCHECK
i.J
1 . Fill in the blarls by choosing the correct alternative
The roots of the seedling absorb water and
mineralsfrom the soil. The leavesstartmanufacturing
food for the young plant which keeps growing and
becomesa mature plant and producesflowers and
seedsin its turn.
(iii)
Very low temp€rarure
embryo (inhibits/destroys).
.. the growth of
(iv)
Germination in pea is
hypogeal).
(v)
Coleoptile is a part found in the germinating ..........
(castor/maize).
(vi)
Alkaline pyrogallic acid is used for absorbing ..........
during experiments on germination
(oxygen/carbon dioxide)
........ (epigeaU
:
i Potr.ITSTO REMEMBER
A dicot seed consisfrof an embryowith two cotyledonsenclosedin a seedcoat.
The embryo consistsof a radicle (smnll root) and a plumule (small shoot)
The cotyledonscontain thefoodfor the embryo
A manocotseedsuch as the maize grain has a single cotyledon,a large endosperm,a small embryo in
which the plumule is small wilh rolled plumule leaves.
Y Three conditions necessaryfor the germinati.on of seedsare water, suitable temperature and orygen.
Y Germination of seedsmay be hypogeal (cotyledonsremaining underground) or epigeal (cotyledonscarried
abovethe soil)
D
Y
Y
Y
REVIEW QUESTIONS
B. VERY SHORTANSWT'RTYPI]
!f_Li;{'fFLF, CHOICE TYPU
i . Are the following statementstrue (T) or false (F) ?
(T/F)
(a) Some seedshave no cotyledonsat all.
Which one of the following plants is correctly
matchedwith one of its statedcharacteristic?
(a) Mango seedaleuronelayer
(b) Bean seed
(c) Maize grain (d) rvheatgrain )
(b) Maize grain is fruit and not a seed.
(T/F)
(c) Seedsfallen in a flower-bed from the previous
crop usually do not germinate until the next
(TlF)
sowing season.
endosperm
coleoptile
exalbuminuous
(d) Oxygen is necessaryfor the germination of
(T/F)
seeds.
Seedssown very deep in the soil fail to germinate
becausethey
l. Name the following :
(a) cannot exert enough force to push the soil
upward
(a) A monocotyledonousendospermicseed.
(b) A chemical usedin experiments,which absorbs
ox)'gen.
(c ) Part of the plumule abovethe embryonic axis of
the seed.
(b) do not get enoughsunlight
(c) get too much water
(d) do not get enoughoxygen
60
(d) A plant which shows viviparous germination.
(e) The layer of endospermof muze, rich in protein.
(0
1
3 . Sometimes the potatoes kept in a basket during the
A seedwith folded plumule leaves.
12. Fill in the blanks :
(a) In bean seeds,
;h
seedsare brought
(b)
of
grows faster and the
ground.
is a protective layer of radicle and
protects the rolled plumule.
tll
(c) A seedis protectedby ..............
and ...........
(d) Seedsabsorb water through .........which also
(e) Rice, wheat,and maize are rich in ...........food.
C. SHORTANSWER TYPE
Etat is the difference between an embryo and a seed?
=
I
I
II
I
2. Give any two examples each of endospermic
(albuminous) seeds, and non-endospermic
(exalbuminous) seeds.
I
3. Germinated grams are considered highly nutritive.
What is the reason for this belief ?
4. Why do we not use the terms maize fruit and muze
seed? What do we say instead?
D. LONG ANSWER TYPE
1. What are the functions of the followins in a seed?
(a) Seedcoat
(b) Micropyle
(c) Cotyledons
(e) Plumule
late rainy seasonstart giving out small shoots.Would
you call it germination? Give reason in suppon of
your answer.
Give two differencesin each of the following pairs :
(a) Epigeal germination and hypogeal germination
(b) Coleorhiza and coleoptile.
(c) Bean seedand maize grain.
.\ Differentiate between germination
and vivipary.
TAMARIND
helps in diffirsion of respiratory gases.
-
Suggest an experiment to prove that a suitable
temperature is necessaryfor germination.
(d) Radicle
tr)
tr)
)us
:xt
F)
of
F)
bs
of
6l
("'fanmr-i-Hind" meaning "Date of India" )
7-lteEnglish name "tamaind" .for thi.s
plant is derivetl .frtm the Parsiun y.'orcl
"Tamar-i-Hind" v,hic:hrueun.s" l)atc
(khtttur)ol lndfu". .ltr.Et
os "khujrrr" i,s
everiwherein "Persiu" stti,: lamoritul
irt Iittiiit.
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