The Flower

A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants. The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs.

In addition to facilitating the reproduction of flowering plants, flowers have long been admired and used by humans to bring beauty to their environment, and also as objects of romance, ritual, religion, medicine and as a source of food.

In this lesson you will learn about :
1) Flower - Definition & Functions
2) Floral Symmetry
3) Pedicellate & Sessile Flowers
4) Insertion of Floral Leaves on the Thalamus
5) Parts of a Flower
6) Some Important Terms related to Flowers
7) Floral Whorls - Calyx, Corolla, Androecium and Gynoecium
8) Placentation
9) Inflorescenece

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1. The Flower

2. Introduction
Aflowerisareproductivepartofanangiospermicplant.It
isconsideredtobeamodifiedshoothavingnodesand
internodesandtheleavesaremodifiedintofloral
structures.
FunctionsofFlower:
BiswarupMajumder| Bio-World
Ithelpsinthesexualreproductionoftheplantby
producingmalegametes(pollengrains)andthefemale
gametes(eggcell).Theunionofthetwogametes
resultsinfertilization.
Ithelpsintheprocessofpollination,i.e.,transference
ofpollengrainfromtheantherstothestigmaofthe
sameorofthedifferentflower.
Ithelpinthedevelopmentofseedsandfruits.
Italsohelpsinthedispersalofseedsandfruits.
Asymmetrical
Flower
Inthistype,the
flowercannotbe
dividedintosimilar
halvesalongany
verticalplane.

3. Thefloweriscommonlyborneonshortorlongstalkcalled
thepedicel(stalkedorpedicellateflower).Someflowers
maybewithoutstalk(sessileflower).
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Receptacle
Stalk
Thetipofflowerstalkmaybeexpandedtoformacup-
shapedreceptacle(thalamus).
Introduction

4. Hypogyny:
Whenthethalamusisconvexorelongated,thecarpeloccupies
thetopmostpositiononit.Theotherfloralmembers(sepals,
petals,andstamens)areplacedbelowthem.Thismodeof
arrangementiscalledhypogyny.Theflowerisdescribedas
hypogynous.Theovaryisknownassuperior.
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Insertion of Floral Leaves on the Thalamus
Perigyny:
Inthiscondition,thereceptacleisflatorslightlycup-shaped.
Thecarpelsaresituatedatitscentreandotherfloral
membersareinsertedonitsmargin.Thismodeofarrangement
iscalledperigyny.Theflowerisknownasperigynous.Inthis
case,theovaryisstilldescribedashalfinferior.
Epigyny:
Whenthethalamusiscupshaped,thelowerpartoftheovary
issituatedatthebottomofthecupandalsofusedwiththe
innerwallofthalamus.Theotherfloralmembersappeartobe
insertedupontheovary.Thismodeonarrangementis
calledepigyny.Thentheflowerissaidtobeepigynous.the
ovaryissaidtobeinferior.

5. Atypicalangiospermicflowerconsistsoffourwhorlsoffloral
appendagesattachedonthereceptacle:
✓Calyx:Itistheoutermostwhorloftheflower.Itiscomposed
ofleaflikegreensepals.Thesepalsareessentiallygreenin
colourbutinsomecasestheyarecolouredlikepetals.Sucha
conditionofcalyxiscalledpetaloid.
✓Corolla:Thisisthesecondwhorloftheflowerandconsistsof
anumberofpetals.Petalsaregenerallybrightlycolouredand
sometimesfragrantwhichmaketheflowertobecome
attractive.
✓Androecium:Itisthethirdwhorlofflowerandisthemale
reproductiveorganconsistingofstamens.Eachstamenismade
offilamentandanther.Thefilamentsupportsantheratitstip.
✓Gynoecium:Thisisthelastandthefourthwhorlofflower
andisthefemalereproductiveorganoftheflower.Itoccupies
thecentralpositiononthereceptacleandcomposedofovary,
styleandstigmaandthecomponentpartsarecalledcarpels.
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Parts of a Flower
Acomplete(orperfect)flowerisone
whichcontainsallfourfloralstructures.
Ifoneormoresetsoffloralstructures
aremissing,thefloweriscalled
incomplete(orimperfect).

6. Essential & Non-essential Parts of a Flower
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Essential(reproductive)partsofaflowerarethosethatare
directlyassociatedwithreproduction.
E.g.,StamenandCarpel(orPistil).
Non-essential(accessory)partsarethosewhicheither
protectthereproductivepartsoftheflowerormakethe
flowerattractiveforpollination.
E.g.,SepalsandPetals.
Insomeflowerscalyxandcorollaareundifferentiatedand
cannotbedistinguished.Theyaretermedperianth.
Whentheperianthisnon-greenitisdescribedaspetaloid.
Whentheperianthisgreenlikethesepals,itisdescribedas
sepaloidperianth.

7. Other Important Terms
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Inaflower,ifallthefourwhorls,i.e.,calyx,corolla,
androeciumandgynoeciumarepresent,theflowerissaidtobe
complete.
Completeflower:
Ifoneormorefloralwhorlislackingintheflower,theflower
issaidtobeincomplete.
Incompleteflower:
Pistillate–Ifthestaminatewhorl(androecium)isabsentor
non-functional,theflowerissaidtobepistillate.Thenon-
functionalstamensarecalledstaminodia.
Staminate–Inthistypeofflower,thepistilorcarpel
(gynoecium)iseithertotallylackingornon-functional.Thenon-
functionalgynoeciumisknownaspistillode.
Neuter–Whenboth,thestaminateandpistillatewhorlsare
lacking,thefloweriscalledneuter,forexample,rayfloretof
sunflower.
BisexualorHermaphrodite:
Theseareflowershavingboththeessentialwhorls,i.e.,the
androeciumandthegynoecium.
Unisexual:
Ifeitheroftheessentialwhorls(i.e.,androeciumorgynoecium)
islacking,theflowerissaidtobeunisexual.
Monoecious–Themaleandfemaleflowersareborneonthe
sameplant,forexample,gourd,maize,cucumber.
Dioecious–Themaleandfemaleflowersareborneonseparate
plants,forexample,mulberry,palm,papaya.
Naked:
Thisconditionariseswhenthefloweriscompletelydevoidof
petalsandsepals,forexample,betel.

8. Calyx
Thecalyxcomposedofsepalsisusuallygreen(sepaloid)and
sometimesotherwisecoloured(petaloid).Itformsthe
outermostnon-essentialwhorloftheflowerandprotectsthe
flowerinthebudstage.Beinggreen,italsomanufacturefood
byphotosynthesis.
Thecalyxmaybe:
Gamosepalous–thesepalsaremoreorlessunited.
Polysepalous–thesepalsarefree.
Generally,thecalyxwithersoffwhenthefruitisformed.
Sometimesitremainsattachedasintomatoandbrinjal.Sucha
calyxiscalledapersistentcalyx.
Functionsofthecalyx:
Protectstheflowerinthebudstage.
Preparesfoodfortheplantbyphotosynthesis.
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Insomeplantsawhorlofgreen
sepalslikestructureispresentat
thebaseofcalyxcalledepicalyx.
Epicalyxisconsideredawhorlof
thebracteolesandmostlyfound
intheflowersoffamilyMalvaceae.
Calyx
Epicalyx
Epicalyx

9. Thecorollaformsthewhorlinnertocalyx.Togetherwiththe
calyx,itprotectstheinneressentialwhorls,thestamensand
pistil.Thepetalsofthecorolla,likethecalyx,maybeunitedto
eachotherormaybefree.
Thecorollamaybe:
Gamopetalous–thepetalsareunited.
Polypetalous–thepetalsarefree.
Thecorollaisgenerallylargeandshowyandassumesvarious
shapesadaptedtoattractinsectsandbringaboutpollination.
Functionsofthecorolla:
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Corolla
Theyattractinsectsforpollinationastheyaregenerally
brightandshowy.
Inthebudstage,thecorollatogetherwiththecalyx,
protectstheinneressentialwhorls.
Bracts Nectaries
A modified leaf or scale, typically small,
with a flower or flower cluster in its axil.
Bracts are sometimes larger and more
brightly colouredthan the true flower.
Thenectariesmakenectar.
Theyareinthecentreoftheflower.
Nectarisasweetsubstance,which
insectsdrinktogivethemenergy.

10. Theandroeciumisthemalereproductivewhorlofaflower,
innertothecorolla.Itiscomposedofanumberofstamens,
eachofwhichconsistsofafilamentandanther.
Theantherisusuallytwolobed.Eachlobehastwopollensacs.
Withinthepollensacsarecontainedpollengrains.Whenfully
maturedthepollensacsrupturetoliberatepollengrains.
Thepollengrainsaregenerallypowderyparticlesofdifferent
shapesandsizes.Eachpollenhastwocoats–theexine(tough,
cutinizedouterprotectivecoat)andtheintine(thindelicate
celluloselayerlyinginternaltotheexine).
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Androecium
Thefilamentsmaybefreefromeachotherandother
structuresortheymaybefusedwitheachotherorfusedwith
thepetalsorgynoecium.Theymayalsovaryinsize.

11. BiswarupMajumder| Bio-World
Types of Androecium
According to the length of the filament:
According to the number of stamens:

12. How to remember the above three terms ?
Mono-,Di-andPoly-respectivelymeansingle,twoandseveral.
Adelphousliterallymeans“groupofbrothers”,herereferringtothepartfromwhichtheanthers
growoutinbundles.Thusthebundleofanthersarisingfromasinglepart(monadelphous),the
bundlesfromtwoparts(diadelphous)andfromseveralparts(polyadelphous).
Adelphous:
Thestamensarefusedbytheirfilamentsonly.Theanthersare
free.Fusionoffilamentsmayproduceasinglegroup
(monadelphous,e.g.,chinarose),twogroups(diadelphous,e.g.,
pea)ormanygroups(polyadelphous,e.g.,citrus).
Syngenesious(=Synantherous):
Stamensarefusedbyanthersonly.Thefilamentsarefree.The
fusedanthersformaringaroundthegynoecium,e.g.,sunflower.
Synandrous:
Stamensarefusedbyboththeirfilamentsaswellasanthers,
e.g.,pumpkin.
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Forms of Cohesion (Fusion) of Stamens

13. BiswarupMajumder| Bio-World
Insertion and Adhesion of Stamens
Fixation of Anthers
Basifixed–Filamentattachedtothebaseoftheanther.
Dorsifixed-Filamentattachedtothedorsal(back)sideof
theanther.
Adnate-Filamentattachedalongtheentirelengthofanther.
Versatile–Filamentattachedtoapointonthebackorbaseof
anthersoastoletitswingfreely.
Divergent–Whentwoantherlobesseparateduetoenlarged
connective.
Distractile–Whentwoantherlobesarefarapart.

14. Gynoecium
Thegynoeciumorpistilisthefemalereproductivepartofthe
flowerandformstheinnermostwhorl.Thepistiliscomposedof
oneormorecarpels.
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Stigma
Terminal knob-like
partofthecarpel.
Style
Tubular stalk
connectingthestigma
andtheovary.
Ovary
Swollenbasalportion.
Theinnercavitymay
containsoneormore
chambers. Each
chambercontainsone
ormoreovules.
Parts

15. BiswarupMajumder| Bio-World
Placentation
Thearrangementofovuleswithintheovaryisknownas
placentation.
Marginal–Theplacentaformsaridgealongtheventral
sutureoftheovaryandtheovulesareborneonthisridge
formingtworows.e.g.,pea.
Axile–Whentheplacentaisaxialandtheovulesare
attachedtoitinamultilocularovary.e.g.,chinarose,
tomatoandlemon.
Parietal–theovulesdevelopontheinnerwalloftheovary
oronperipheralpart.Ovaryisone-chamberedbutit
becomestwochamberedduetotheformationofthefalse
septum(replum)e.g.,mustardandArgemone.
Basal–theplacentadevelopsatthebaseofovaryanda
singleovuleisattachedtoit.e.g.,sunflower,marigold.
FreeCentral–Whentheovulesareborneoncentralaxis
andseptaareabsent.e.g.,Dianthus,Primrose.
Ovules turn into seedsin the mature fruit
(transformed ovary). their different
arrangements can be seen in fruits such as
those of pea, tomato, mango, lotus, etc.
TypesofPlacentation:

16. BiswarupMajumder| Bio-World
Inflorescenceisthemodeofarrangementofflowersonthe
axisoftheplant.
TypesofInflorescence:
Inflorescence
The flowers may be arranged in several different ways in different plants, this manner
of arrangement is termed as inflorescence.