Editing Pollen (section)

==Pollination==
{{Main article|Pollination}}
[[File:Apis mellifera flying.jpg|thumb|[[Apis mellifera|European honey bee]] carrying pollen in a [[pollen basket]] back to the hive]]
[[File:Episyrphus balteatus - head close-up (aka).jpg|thumb|[[Episyrphus balteatus|Marmalade hoverfly]], pollen on its face and legs, sitting on a [[Cistus|rockrose]].]]
[[File:Diadasia Bee Straddles Cactus Flower Carpels close-up.jpg|thumb|right|''[[Diadasia]]'' bee straddles flower [[carpels]] while visiting yellow ''[[Opuntia engelmannii]]'' [[cactus]] ]]
The transfer of pollen grains to the female reproductive structure ('''''[[pistil]]''''' in angiosperms) is called '''[[pollination]]'''. Pollen transfer is frequently portrayed as a sequential process that begins with placement on the vector, moves through travel, and ends with deposition.<ref>{{Cite journal |last1=Minnaar |first1=Corneile |last2=Anderson |first2=Bruce |last3=de Jager |first3=Marinus L |last4=Karron |first4=Jeffrey D |date=2019-01-23 |title=Plant–pollinator interactions along the pathway to paternity |url=https://academic.oup.com/aob/article/123/2/225/5232516 |journal=Annals of Botany |language=en |volume=123 |issue=2 |pages=225–245 |doi=10.1093/aob/mcy167 |issn=0305-7364 |pmc=6344347 |pmid=30535041}}</ref> This transfer can be mediated by the wind, in which case the plant is described as '''[[Anemophily|anemophilous]]''' (literally wind-loving). Anemophilous plants typically produce great quantities of very lightweight pollen grains, sometimes with air-sacs.

Non-flowering seed plants (e.g., pine trees) are characteristically anemophilous. Anemophilous flowering plants generally have inconspicuous flowers. '''[[Entomophily|Entomophilous]]''' (literally insect-loving) plants produce pollen that is relatively heavy, sticky and [[protein]]-rich, for dispersal by [[insect]] [[pollinator]]s attracted to their flowers. Many insects and some [[mite]]s are specialized to feed on pollen, and are called [[palynivore]]s.

In non-flowering seed plants, pollen germinates in the pollen chamber, located beneath the [[Ovule|micropyle]], underneath the integuments of the ovule. A [[pollen tube]] is produced, which grows into the [[nucellus]] to provide nutrients for the developing sperm cells. Sperm cells of [[Pinophyta]] and [[Gnetophyta]] are without [[flagella]], and are carried by the pollen tube, while those of [[Cycad]]ophyta and [[Ginkgophyta]] have many flagella.

When placed on the [[stigma (botany)|stigma]] of a flowering plant, under favorable circumstances, a pollen grain puts forth a [[pollen tube]], which grows down the tissue of the style to the [[ovary (plants)|ovary]], and makes its way along the [[Placentation#In plants|placenta]], guided by projections or hairs, to the micropyle of an [[ovule]]. The nucleus of the tube cell has meanwhile passed into the tube, as does also the generative nucleus, which divides (if it has not already) to form two sperm cells. The sperm cells are carried to their destination in the tip of the pollen tube. Double-strand breaks in DNA that arise during pollen tube growth appear to be efficiently [[DNA repair|repaired]] in the generative cell that carries the male [[genome|genomic information]] to be passed on to the next plant generation.<ref name="pmid23550213">{{cite journal |vauthors=Hirano T, Takagi K, Hoshino Y, Abe T |title=DNA damage response in male gametes of Cyrtanthus mackenii during pollen tube growth |journal=AoB Plants |volume=5 |pages=plt004 |year=2013 |pmid=23550213 |pmc=3583183 |doi=10.1093/aobpla/plt004}}</ref> However, the vegetative cell that is responsible for tube elongation appears to lack this [[DNA repair]] capability.<ref name="pmid23550213" />