Editing Pollination (section)

=={{anchor|Mechanics}}Mechanism==
[[File:Diadasia Bee Straddles Cactus Flower Carpels close-up.jpg|thumb|upright|''[[Diadasia]]'' bee straddles [[cactus]] [[carpels]]]]
[[File:Hymenoptera,_Vespidae,_Polistinae,_Mischocyttarus_rotundicollis.jpg|thumb|The wasp ''Mischocyttarus rotundicollis'' transporting pollen grains of ''[[Schinus terebinthifolius]]'' ]]

Pollination can be accomplished by '''cross-pollination''' or by [[self-pollination]]:
* Cross-pollination, also called ''[[allogamy]]'', occurs when pollen is delivered from the stamen of one flower to the stigma of a flower on another plant of the same species.<ref name=Campbell>{{cite book |title=Biology |last1=Campbell |first1=Neil A. |last2=Reece |first2=Jane B. | name-list-style = vanc |year=2002 |publisher=Pearson Education |isbn=978-0-201-75054-6 |pages=600–612 |edition=6th }}</ref> Plants adapted for cross-pollination have several mechanisms to prevent self-pollination; the reproductive organs may be arranged in such a way that self-fertilisation is unlikely, or the stamens and carpels may mature at different times.<ref name=Campbell/>
* Self-pollination occurs when pollen from one flower pollinates the same flower or other flowers of the same individual.<ref>{{Cite book | vauthors = Cronk JK, Fennessy MS | title=Wetland plants: biology and ecology | year=2001 | publisher=Lewis Publishers | location=Boca Raton, Fla.  | isbn=978-1-56670-372-7 | page=166}}</ref>  It is thought to have evolved under conditions when pollinators were not reliable vectors for pollen transport, and is most often seen in short-lived annual species and plants that colonize new locations.<ref name=Glover2007>{{Cite book| title=Understanding flowers and flowering: an integrated approach| year=2007| last = Glover | first = Beverly J.| name-list-style = vanc | publisher=Oxford University Press| page=127| isbn=978-0-19-856596-3}}</ref> Self-pollination may include ''autogamy'', where pollen is transferred from anther (male part) to the stigma (female part) of the same flower; or ''geitonogamy'', when pollen is transferred from anther of a flower to stigma  of another flower on the same plant.<ref name=Class9/> Plants adapted to self-fertilize often have similar stamen and carpel lengths. Plants that can pollinate themselves and produce viable offspring are called self-fertile. Plants that cannot fertilize themselves are called self-sterile, a condition which mandates cross-pollination for the production of offspring.<ref name=Class9>{{cite book|title=New Living Science: Biology for Class 9|url=https://books.google.com/books?id=o9pZiJdmedwC&pg=PA56 |publisher=Ratna Sagar |isbn=978-81-8332-565-3 |pages=56–61}}</ref>
*''[[Cleistogamy]]'': is self-pollination that occurs before the flower opens.  The pollen is released from the anther within the flower or the pollen on the anther grows a tube down the style to the ovules. It is a type of sexual breeding, in contrast to asexual systems such as apomixis.  Some ''cleistogamous'' flowers never open, in contrast to ''[[chasmogamous]]'' flowers that open and are then pollinated. Cleistogamous flowers are by necessity found on self-compatible or self-fertile plants.<ref name=CulleyJAN-07>{{Cite journal | last1=Culley | first1=Theresa M. | last2=Klooster | first2=Matthew R. | name-list-style = vanc |year=2007 | title=The cleistogamous breeding system: a review of its frequency, evolution, and ecology in angiosperms | journal=The Botanical Review | url=http://www.accessmylibrary.com/coms2/summary_0286-30779368_ITM | doi=10.1663/0006-8101(2007)73[1:TCBSAR]2.0.CO;2 | volume=73 | pages=1–30| s2cid=12223087 | url-access=subscription }}</ref> Although certain orchids and grasses are entirely cleistogamous, other plants resort to this strategy under adverse conditions. Often there may be a mixture of both cleistogamous and chasmogamous flowers, sometimes on different parts of the plant and sometimes in mixed inflorescences. The [[Amphicarpaea bracteata|ground bean]] produces cleistogamous flowers below ground, and mixed cleistogamous and chasmogamous flowers above.<ref name=Baskin>{{cite book| last1 = Baskin | first1 = Carol C.| last2 = Baskin | first2 = Jerry M. | name-list-style = vanc |title=Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination |url=https://books.google.com/books?id=uGJL_Ys6wlQC&pg=PA215 |year=2001 |publisher=Elsevier |isbn=978-0-12-080263-0 |page=215}}</ref>

<gallery mode="packed">
File:Geranium incanum 9154s.jpg|''Geranium incanum'', like most geraniums and pelargoniums, sheds its anthers, sometimes its stamens as well, as a barrier to self-pollination. This young flower is about to open its anthers, but has not yet fully developed its pistil.
File:Geranium incanum 9159s.jpg|The lower two of these ''Geranium incanum'' flowers have opened their anthers, but not yet their stigmas. Note the change of colour that signals to pollinators that they are ready for visits.  The uppermost flower is somewhat more mature than the others and has already shed its stamens.
File:Geranium incanum 9156s.jpg|This ''Geranium incanum'' flower has shed its stamens, and deployed the tips of its pistil without accepting pollen from its own anthers. (It might of course still receive pollen from younger flowers on the same plant.)
</gallery>

An estimated 48.7% of plant species are either [[Dioecy#In botany|dioecious]] or [[Self-incompatibility in plants|self-incompatible]] obligate out-crossers.<ref name="pmid16817548">{{cite journal | vauthors = Igic B, Kohn JR | title = The distribution of plant mating systems: study bias against obligately outcrossing species | journal = Evolution; International Journal of Organic Evolution | volume = 60 | issue = 5 | pages = 1098–103 | date = May 2006 | pmid = 16817548 | doi = 10.1554/05-383.1 | s2cid = 40964 }}</ref>  It is also estimated that about 42% of flowering plants have a mixed mating system in nature.<ref>{{cite journal | vauthors = Goodwillie C, Kalisz S, Eckert CG | date = 2005 | title = The evolutionary enigma of mixed mating systems in plants: Occurrence, theoretical explanations, and empirical evidence.  | journal = Annu. Rev. Ecol. Evol. Syst. | volume = 36 | pages = 47–79 | doi = 10.1146/annurev.ecolsys.36.091704.175539 }}</ref>  In the most common kind of mixed mating system, individual plants produce a single type of flower and fruits may contain self-pollinated, out-crossed or a mixture of progeny types.

Pollination also requires consideration of [[pollenizer]]s, the plants that serve as the pollen source for other plants. Some plants are ''[[Self-compatibility in plants|self-compatible]]'' (''self-fertile'') and can pollinate and fertilize themselves. Other plants have chemical or physical barriers to [[self-pollination]].

In agriculture and [[horticulture]] pollination management, a good pollenizer is a plant that provides compatible, viable and plentiful pollen and blooms at the same time as the plant that is to be pollinated or has pollen that can be stored and used when needed to pollinate the desired flowers. [[Hybrid (biology)|Hybridization]] is effective pollination between flowers of different [[species]], or between different breeding lines or populations. see also [[Heterosis]].

[[Peach]]es are considered self-fertile because a commercial crop can be produced without cross-pollination, though cross-pollination usually gives a better crop. Apples are considered [[Self-incompatibility in plants|self-incompatible]], because a commercial crop must be cross-pollinated. Many commercial fruit tree varieties are [[grafting|grafted]] [[cloning|clone]]s, [[genetics|genetically]] identical. An orchard block of apples of one variety is genetically a single plant. Many growers now consider this a mistake. One means of correcting this mistake is to graft a limb of an appropriate pollenizer (generally a variety of [[crabapple]]) every six trees or so.{{Citation needed|date=August 2009}}