Pollination

Pollination in plants is the process where pollen is transferred from the anther, the male part of a flower, to the stigma, the female part of a flower. Pollen can be transferred to one plant or even a nearby plant so that they can get fertilized and make more flowers. This happens in plants that have flowers called angiosperms.

In this lesson you will learn about :
1) What is Pollination?
2) Types of Pollination
3) Self-Pollination
- Adaptations for Self-Pollination
- Advantages and Disadvantages of Self-Pollination
4) Cross-Pollination
- Adaptations for Cross-Pollination
- Advantages and Disadvantages of Cross-Pollination
5) Agents of Cross-Pollination
- Entomophilous
- Anemophilous
- Hydrophilous
6) Artificial Pollination

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1. Pollination

2. Introduction
Thefloweristhepartoftheplantthatbringsabout
reproductionbysexualmeans.
Theandroeciumandgynoeciumproducethemaleand
femalegametesrespectively,whichonfusion,formthe
zygote.
Thefusionofthemaleandfemalegametesistermed
asfertilization.Inordertobringaboutfertilization,
themostimportantstepistobringthetwogametes
together.Thisisbroughtaboutbyaprocesscalled
pollination.
Therearetwokindsofpollination:self-pollinationand
cross-pollination.
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3. Pollination
Pollinationisthetransferenceofpollengrainsfromthe
antherofaflowertothestigmaofaflower.
Itmayhappeninthreeprincipalways–
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Autogamy(auto:self,gamy:marriage)
Geitonogamy(geitono:neighbouring,gamy:marriage)
Allogamy(allo:other,gamy:marriage)
Thepollenofthesameflowermayfallonitsstigmaby
itself.
Thepollenofanotherflowerofthesameplantmayfall
onitsstigma.
Thepollenofaflowerofanotherplantofthesame
speciesmayfallonitsstigma.
Pollinationmustoccurbetweenplantsofthesame
species.Naturehassodesignedthatonlythepollenof
thesamespeciesofplantwillsurviveandgrowfurther
tocontinuetheprocessforreproductionandtherest
ofthetypesofpollenwillfailtogerminateandperish.

4. The word ‘pollen’, was used in science writing since 1760 and means “the fertilizing
part of flowers”. Earlier in history it meant “dust or fine flour”.
Self-Pollination
Inselfpollination,thepollenproducedbytheantherof
thefloweristransferredtothestigmaofthesame
flowerortothestigmaofanotherflowerborneonthe
sameplant.
Adaptationsforself-pollination:
Self-pollinationcanoccurinbisexualflowersaswellas
monoeciousunisexualflowers.
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Homogamy:
Cleistogamy:
Simultaneousmaturationofanthersandstigma.
Toensurethatselfpollinationtakesplace,the
antherandstigmaofthebisexualflowerorthoseof
theunisexualflowersmustmatureatthesametime.
Examples:Mirabilis,Gardenia,etc.
Thisisaconditioninwhichtheflowersremain
closed.
Therearesomebisexualflowersthatneveropen.As
aresult,thepollengrainaredistributedonthe
stigmaofthesameflower.
Suchflowersaresmall,inconspicuousandlackcolour
andfragrance.
Examples:Commelina,wood-sorrel,etc.

5. Lessvarietiesofoffspringareproducedastheoffspring’s
genesaresimilartothoseoftheparentplant,therefore
thespeciesislessadaptedtochangesintheenvironment.
Continuedself-pollinationmayleadtooffspringbecoming
weaker,smallerandlessresistanttodiseases.
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Advantages of Self-Pollination
Only one parent is required.
Offspringinheritsitsgenesfromparentplant.Hence
beneficialqualitiesaremorelikelytobepasseddownto
theoffspring.
Itdoesnotdependonexternalfactorse.g.insectsorwind
forpollination.
Anthersareclosetothestigmasofthesameflowerhence
thereisahighpossibilitythatselfpollinationwilloccur.
Lesspollenandenergyiswastedisself-pollination
comparedtocrosspollination.
Disadvantages of Self-Pollination
Self-Pollination

6. Cross-Pollination
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Crosspollinationisthetransferofpollenfromthe
anthersofflowersofoneplanttothestigmaofa
flowerofanotherplantofthesamespecies.
Thistransferencecanoccurthroughwind,insectsor
otheragents.
Naturefavourscrosspollination.Thevastmajorityof
floweringplantsarecross-pollinated.
Incompatibility
Incrosspollinatedplants,thepollen
fromacertainspeciesoftenreachesthe
stigmaofadifferentspecies.
However,thechemicalspresentinthe
stigmafailtostimulatethegrowthofthe
pollentubeandhencenofertilization
occursbetweenplantsofdifferent
species.

7. Adaptations for Cross-Pollination
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Unisexuality:
Dichogamy:
Theflowersshouldbeeithermaleorfemaleorborne
onseparateplants,i.e.,unisexualdioecious.
Examples:palm,papaya,etc.
Incaseofbisexualflowers,themaleandfemalewhorls
mustmatureatdifferenttimes.
Protandry-theanthersoftheflowermature
beforethestigma,e.g.sunflower,sweatpea,etc.
Protogyny-thestigmaoftheflowermaturebefore
theanthers,e.g.custardapple,peepal,etc.
Herkogamy:
Self-sterility:
Theflowerspossessstructuralfeatureswhichdonot
allowselfpollination.
Example:inpansy,ahoodcoversthestigma.
Thepollenfromtheantherfailtogerminateonthe
stigmaoftheflower.
Examples:rayfloretsofsunflower,orchids,etc.
Heterostyly:
Flowershavestylesofdifferentlengthsandanthers
situatedatdifferentheightsuponthecorollatube.
Examples:primrose,Oxalis,etc.

8. Twoparentplantsarerequired.
Dependsonexternalfactorse.g.insectsorwindfor
pollination.
Lowerprobabilitythatcrosspollinationwilloccur
comparedtoself-pollination(becauseitinvolvestransfer
ofpollengrainsfromtheantherofoneplanttothestigma
ofanotherplant).
Moreenergyandpolleniswastedascomparedtoself-
pollination.
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Advantages of Cross-Pollination
Offspringmayhaveinheritedbeneficialqualitiesfrom
bothparents.
Abundantandmoreviableseedstendtobeproduced(i.e.
seedsarecapableofsurvivinglongerbeforegermination).
Morevarietiesofoffspringcanbeproduced(greater
geneticvariation).
Disadvantages of Cross-Pollination
Increaseschanceofsurvivalofspeciestochangesin
theenvironment.

9. Comparison
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10. Agents of Cross-Pollination
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Entomophilous(entomon:insect,phile:affinity)
Insectpollinatedflowers(Example:Pea)usuallyhavethe
followingcharacteristics–
Insect pollinators
Bees
Wasps
Flies
Butterflies
Some beetles

11. Agents of Cross-Pollination
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Anemophilous(anemo:wind,phile:affinity)
Windpollinatedflowers(Example:Maize)usuallyhavethe
followingcharacteristics–

12. Thehoneybeedancelanguage,used
torecruitnestmatestofood
sources,isregardedbymanyasone
ofthemostintriguingcommunication
systemsinanimals.
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Comparison

13. Agents of Cross-Pollination
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Hydrophilous(hydro:water,phile:affinity)
Flowersarefoundonlyinaquaticplants(Example:
Vallisneria).Theyhavethefollowingcharacteristics–
1.Flowersaresmallandinconspicuous.
2.Nectarandodourareabsent.
3.Pollengrainsarelightandnon-wettableduetothe
presenceofmucilagecover.
4.Stigmaislong,sickybutwettable.
Types:
Epihydrophily Hypohydrophily
Epihydrophily–pollinationoccursoverthesurfaceof
water.
Hypohydrophily-pollinationoccursbelowthesurface
ofwater.

14. Artificial Pollination
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Procedure
When manhimself
transferspollentothe
stigmaitiscalled
artificialpollination.
In the ancient
civilization of
Babylonia,itwasa
commonpracticeto
sprinkle“maleflowers”
ofpalmsonthe
“female”flowers;of
course,atthattime
theyneitherknewthe
sexualityofpalm
flowersnoranything
aboutpollination.