Editing Fertilisation (section)

===Flowering plants===
{{main|Double fertilisation}}

After being fertilised, the ovary starts to swell and develop into the [[fruit]].<ref name="facts_and_practice_for_a_level">{{cite book |last1=Johnstone |first1=Adam |title=Biology: facts & practice for A level |publisher=Oxford University Press |isbn=0-19-914766-3 |page=[https://archive.org/details/biologyfactsprac0000john/page/95 95] |year=2001 |url=https://archive.org/details/biologyfactsprac0000john/page/95 }}</ref> With multi-seeded fruits, multiple grains of pollen are necessary for syngamy with each ovule.  The growth of the pollen tube is controlled by the vegetative (or tube) cytoplasm. Hydrolytic [[enzymes]] are secreted by the pollen tube that digest the female tissue as the tube grows down the stigma and style; the digested tissue is used as a nutrient source for the pollen tube as it grows. During pollen tube growth towards the ovary, the generative nucleus divides to produce two separate sperm nuclei (haploid number of chromosomes)<ref name="handbook_of_plant_science">{{cite book |title=Handbook of plant science |year=2007 |publisher=John Wiley |location=Chichester, West Sussex, England |isbn=978-0-470-05723-0 |page=466}}</ref> – a growing pollen tube therefore contains three separate nuclei, two sperm and one tube.<ref name="biology_today_a01">{{cite book |last1=Kirk |first1=David |last2=Starr |first2=Cecie |title=Biology today |year=1975 |publisher=CRM |location=Del Mar, Calif. |isbn=978-0-394-31093-0 |page=[https://archive.org/details/biologytoday00kirk/page/93 93] |url=https://archive.org/details/biologytoday00kirk |url-access=registration }}</ref> The sperms are interconnected and dimorphic, the large one, in a number of plants, is also linked to the tube nucleus and the interconnected sperm and the tube nucleus form the "male germ unit".<ref>{{cite book |last1=Raghavan |first1=Valayamghat |title=Double fertilization: embryo and endosperm development in flowering plant |url=https://archive.org/details/fertilizationhig00ragh |url-access=limited |year=2006 |publisher=Springer-Verlag |location=Berlin |isbn=978-3-540-27791-0 |page=[https://archive.org/details/fertilizationhig00ragh/page/n235 12]}}</ref>

Double fertilisation is the process in [[angiosperms]] (flowering plants) in which two [[sperm]] from each pollen tube fertilise two [[cell (biology)|cells]] in a female [[gametophyte]] (sometimes called an embryo sac) that is inside an ovule. After the pollen tube enters the gametophyte, the pollen tube nucleus disintegrates and the two sperm cells are released; one of the two sperm cells ''fertilises'' the egg cell (at the bottom of the gametophyte near the micropyle), forming a [[diploid]] (2n) [[zygote]]. This is the point when fertilisation actually occurs; pollination and fertilisation are two separate processes. The nucleus of the other sperm cell fuses with two haploid polar nuclei (contained in the central cell) in the centre of the gametophyte. The resulting cell is [[triploid]] (3n). This triploid cell divides through [[mitosis]] and forms the [[endosperm]], a [[nutrient]]-rich [[tissue (biology)|tissue]], inside the [[seed]].<ref name=Faure1999/> The two central-cell maternal nuclei (polar nuclei) that contribute to the endosperm arise by mitosis from the single meiotic product that also gave rise to the egg. Therefore, maternal contribution to the genetic constitution of the triploid endosperm is double that of the embryo.

One primitive species of flowering plant, ''[[Nuphar|Nuphar polysepala]]'', has endosperm that is diploid, resulting from the fusion of a sperm with one, rather than two, maternal nuclei. It is believed that early in the development of angiosperm lineages, there was a duplication in this mode of reproduction, producing seven-celled/eight-nucleate female gametophytes, and triploid endosperms with a 2:1 maternal to paternal genome ratio.<ref name=Friedman2003>{{cite journal |doi=10.1111/j.0014-3820.2003.tb00257.x |pmid=12683519 |title=Modularity of the Angiosperm Female Gametophyte and Its Bearing on the Early Evolution of Endosperm in Flowering Plants |journal=Evolution |volume=57 |issue=2 |pages=216–30 |year=2003 |last1=Friedman |first1=William E |last2=Williams |first2=Joseph H |doi-access=free }}</ref>

In many plants, the development of the flesh of the fruit is proportional to the percentage of fertilised ovules. For example, with [[watermelon]], about a thousand grains of pollen must be delivered and spread evenly on the three lobes of the stigma to make a normal sized and shaped fruit.{{citation needed|date=January 2024}}
{{anchor#Animals}}
{{anchor|Fertilisation in animals}}