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-[[Image:Sunflower seedlings.jpg|thumb|right|250px|[[Sunflower]] seedlings, just three days after germination]]
-[[Image:Kiemtafel (germination table).jpg|thumb|250px|right|Germination rate testing on the germination table]]
-'''Germination''' is the process in which a plant or fungus emerges from a seed or spore and begins growth. The most common example of germination is the [[sprouting]] of a [[seedling]] from a [[seed]] of an [[flowering plant|angiosperm]] or [[gymnosperm]]. However the growth of a [[sporeling]] from a [[spore]], for example the growth of [[hypha]]e from [[Fungus|fungal]] spores, is also germination. In a more general sense, germination can imply anything expanding into greater being from a small existence or [[Germ cell|germ]].
-==Seed germination==
-[[Image:Raapstelen gekiemde zaden (Brassica campestris germinating seeds).jpg|thumb|250px|''[[Brassica|Brassica campestris]]'' germinating seeds]]
-[[Image:- Eranthis hyemalis - Seedling -.jpg|thumb|250px|A germinated seedling (''[[Eranthis hyemalis]]'') emerges from the ground]]
-[[File:Mung bean germination.ogv|right|250px|Time lapse video of mung bean seeds germinating]]
-Germination is the growth of an [[embryo]]nic plant contained within a seed; it results in the formation of the seedling. The seed of a [[higher plant]] is a small package produced in a [[fruit]] or [[conifer cone|cone]] after the union of male and female sex cells. All fully developed seeds contain an [[embryo]] and, in most plant species some store of food reserves, wrapped in a seed coat.  Some plants produce varying numbers of seeds that lack embryos, these are called [[empty seed]]s,<ref>http://www.fao.org/DOCREP/006/AD232E/AD232E20.htm</ref> and never germinate. Most seeds go through a period of [[quiescence]] where there is no active growth; during this time the seed can be safely transported to a new location and/or survive adverse [[climate]] conditions until circumstances are favorable for growth. Quiescent seeds are ripe seeds that do not germinate because they are subject to external environmental conditions that prevent the initiation of metabolic processes and cell growth. Under favorable conditions, the seed begins to germinate and the embryonic tissues resume growth, developing towards a seedling.
-==== Requirements for seed germination ====
-Seed germination depends on both internal and external conditions. The most important external factors include [[temperature]], [[water]], [[oxygen]] and sometimes [[light]] or darkness.<ref name="Raven"/> Various plants require different variables for successful seed germination, often this depends on the individual seed variety and is closely linked to the [[Ecology|ecological conditions]] of a plant's [[natural habitat]].  For some seeds, their future germination response is affected by environmental conditions during seed formation; most often these responses are types of [[seed dormancy]].
-* '''Water''' - is required for germination. Mature seeds are often extremely dry and need to take in significant amounts of water, relative to the dry weight of the seed, before cellular [[metabolism]] and growth can resume. Most seeds need enough water to moisten the seeds but not enough to soak them.  The uptake of water by seeds is called [[imbibition]], which leads to the swelling and the breaking of the seed coat. When seeds are formed, most plants store a food reserve with the seed, such as [[starch]], [[protein]]s, or [[oil]]s. This food reserve provides nourishment to the growing embryo. When the seed imbibes water, [[hydrolytic enzyme]]s are activated which break down these stored food resources into metabolically useful [[chemical]]s.<ref name="Raven"/>  After the seedling emerges from the seed coat and starts growing roots and leaves, the seedling's food reserves are typically exhausted; at this point photosynthesis provides the energy needed for continued growth and the seedling now requires a continuous supply of water, nutrients, and light.
-* '''Oxygen''' - is required by the germinating seed for [[metabolism]].<ref>S. M. Siegel, L. A. Rosen (1962) ''Effects of Reduced Oxygen Tension on Germination and Seedling Growth'' Physiologia Plantarum 15 (3), 437–444 doi:10.1111/j.1399-3054.1962.tb08047.x</ref>  Oxygen is used in [[aerobic respiration]], the main source of the seedling's energy until it grows leaves.<ref name="Raven"/> Oxygen is an [[atmospheric gas]] that is found in [[soil]] pore spaces; if a seed is buried too deeply within the soil or the soil is waterlogged, the seed can be oxygen starved.  Some seeds have impermeable seed coats that prevent oxygen from entering the seed, causing a type of physical dormancy which is broken when the seed coat is worn away enough to allow gas exchange and water uptake from the environment.
-* '''Temperature''' - affects cellular metabolic and growth rates. Seeds from different species and even seeds from the same plant germinate over a wide range of temperatures. Seeds often have a temperature range within which they will germinate, and they will not do so above or below this range. Many seeds germinate at temperatures slightly above room-temperature 60-75 F (16-24 C), while others germinate just above freezing and others germinate only in response to alternations in temperature between warm and cool. Some seeds germinate when the soil is cool 28-40 F (-2 - 4 C), and some when the soil is warm 76-90 F (24-32 C).  Some seeds require exposure to cold temperatures ([[vernalization]]) to break dormancy. Seeds in a dormant state will not germinate even if conditions are favorable. Seeds that are dependent on temperature to end dormancy have a type of physiological dormancy.  For example, seeds requiring the cold of winter are inhibited from germinating until they take in water in the fall and experience cooler temperatures. Four degrees [[Celsius]] is cool enough to end dormancy for most cool dormant seeds, but some groups, especially within the family [[Ranunculaceae]] and others, need conditions cooler than -5 C. Some seeds will only germinate after hot temperatures during a [[forest fire]] which cracks their seed coats; this is a type of physical dormancy.
-Most common annual [[vegetable]]s have optimal germination temperatures between 75-90 F (24-32 C), though many species (e.g. [[radish]]es or [[spinach]]) can germinate at significantly lower temperatures, as low as 40 F (4 C), thus allowing them to be grown from seed in cooler climates. Suboptimal temperatures lead to lower success rates and longer germination periods.
-* '''Light or darkness''' - can be an environmental trigger for germination and is a type of physiological dormancy. Most seeds are not affected by light or darkness, but many seeds, including species found in forest settings, will not germinate until an opening in the canopy allows sufficient light for growth of the seedling.<ref name="Raven"/>
-Scarification mimics natural processes that weaken the seed coat before germination. In nature, some seeds require particular conditions to germinate, such as the heat of a fire (e.g., many Australian native plants), or soaking in a body of water for a long period of time. Others need to be passed through an animal's [[digestive tract]] to weaken the seed coat enough to allow the seedling to emerge.<ref name="Raven"/>
-[[Image:Sjb whiskey malt.jpg|thumb|250px|Malted (germinated) [[barley]] grains]]
-=== Dormancy ===
-Some live seeds are [[dormancy|dormant]] and need more time, and/or need to be subjected to specific environmental conditions before they will germinate. [[Seed dormancy]] can originate in different parts of the seed, for example, within the embryo; in other cases the seed coat is involved. Dormancy breaking often involves changes in membranes, initiated by dormancy-breaking signals. This generally occurs only within hydrated seeds.<ref>{{Cite book| title = The encyclopedia of seeds: science, technology and uses Cabi Series| url = http://books.google.com/books?id=aE414KuXu4gC&pg=PA203| year = 2006| journal = CABI| pages = 203| isbn = 0851997236| last1 = Derek Bewley | first1 =  J.| last2 =  Black | first2 =  Michael| last3 =  Halmer | first3 =  Peter| accessdate = 2009-08-28| postscript = <!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->}}</ref> Factors affecting seed dormancy include the presence of certain plant hormones, notably [[abscisic acid]], which inhibits germination, and [[gibberellin]], which ends seed dormancy. In [[brewing]], barley seeds are treated with gibberellin to ensure uniform seed germination for the production of barley [[malt]].<ref name="Raven"/>
-=== Seedling establishment ===
-In some definitions, the appearance of the [[radicle]] marks the end of germination and the beginning of "establishment", a period that ends when the seedling has exhausted the food reserves stored in the seed. Germination and establishment as an independent organism are critical phases in the life of a plant when they are the most vulnerable to injury, disease, and water stress.<ref name="Raven"/> The germination index can be used as an indicator of [[phytotoxicity]] in soils. The mortality between dispersal of seeds and completion of establishment can be so high that many species have adapted to produce huge numbers of seeds.
-==Germination rate==
-In [[agriculture]] and [[gardening]], the '''germination rate''' describes how many seeds of a particular [[plant]] [[species]], variety or seedlot are likely to germinate. It is usually expressed as a percentage, e.g., an 85% germination rate indicates that about 85 out of 100 seeds will probably germinate under proper conditions. The germination rate is useful for calculating the seed requirements for a given area or desired number of plants.
-=== Dicot germination ===
-The part of the plant that first emerges from the seed is the embryonic root, termed the [[radicle]] or primary root. It allows the seedling to become anchored in the ground and start absorbing water. After the root absorbs water, an embryonic shoot emerges from the seed. This shoot comprises three main parts: the [[cotyledon]]s (seed leaves), the section of shoot below the cotyledons ([[hypocotyl]]), and the section of shoot above the cotyledons ([[epicotyl]]). The way the shoot emerges differs among plant groups.<ref name="Raven">{{cite book | last = Raven | first = Peter H. | coauthors = Ray F. Evert, Susan E. Eichhorn | title = Biology of Plants, 7th Edition | publisher = W.H. Freeman and Company Publishers | year = 2005 | location = New York | pages = 504–508 | isbn = 0-7167-1007-2}}</ref>
-==== Epigeous ====
-In '''epigeous''' (or [[epigeal]]) germination, the ''hypocotyl'' elongates and forms a hook, pulling rather than pushing the [[cotyledon]]s and [[apical meristem]] through the soil. Once it reaches the surface, it straightens and pulls the cotyledons and shoot tip of the growing seedlings into the air. [[Bean]]s, tamarind, and papaya are examples of plants that germinate this way.<ref name="Raven"/>
-==== Hypogeous ====
-Another way of germination is hypogeous (or hypogeal), where the epicotyl elongates and forms the hook. In this type of germination, the cotyledons stay underground where they eventually decompose. Peas, for example, germinate this way.<ref name="Raven"/>
-Germination starts with one tiny seedling which begins to sprout.
-=== Monocot germination ===
-In [[monocot]] seeds, the embryo's radicle and cotyledon are covered by a [[coleorhiza]] and [[coleoptile]], respectively. The coleorhiza is the first part to grow out of the seed, followed by the radicle. The coleoptile is then pushed up through the ground until it reaches the surface. There, it stops elongating and the first leaves emerge.<ref name="Raven"/>
-=== Precocious germination ===
-While not a class of germination, precocious germination refers to seed germination before the fruit has released seed.<ref name=editor1998>{{Cite book| last = editor| year = 1998| title = Crop sciences : recent advances| pages = 177| isbn = 156022059 | publisher = Food Products Press| location = New York| postscript = <!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->}}</ref> The seeds of the green apple commonly germinate in this manner.{{Citation needed|date=December 2007}}
-== Pollen germination ==
-Another germination event during the life cycle of [[gymnosperm]]s and [[flowering plant]]s is the germination of a pollen grain after [[pollination]]. Like seeds, [[pollen]] grains are severely dehydrated before being released to facilitate their dispersal from one plant to another. They consist of a protective coat containing several cells (up to 8 in gymnosperms, 2-3 in flowering plants). One of these cells is a [[tube cell (plant)|tube cell]]. Once the pollen grain lands on the stigma of a receptive [[flower]] (or a female [[Conifer cone|cone]] in gymnosperms), it takes up water and germinates. Pollen germination is facilitated by [[hydration]] on the stigma, as well as by the structure and [[physiology]] of the stigma and style.<ref name="Raven"/> Pollen can also be induced to germinate ''in vitro'' (in a [[petri dish]] or test tube).<ref name="Martin">{{cite journal |author=Martin FW |title=In Vitro Measurement of Pollen Tube Growth Inhibition |journal=Plant Physiol |volume=49 |issue=6 |pages=924–925 |year=1972 |pmid=16658085 |pmc=366081 |doi=10.1104/pp.49.6.924}}</ref><ref name="Pfahler">{{cite journal |author=Pfahler PL |title=In vitro germination characteristics of maize pollen to detect biological activity of environmental pollutants |url=http://jstor.org/stable/3429260 |journal=Environ. Health Perspect. |volume=37 |issue= |pages=125–32 |year=1981 |pmid=7460877 |pmc=1568653|doi=10.2307/3429260}}</ref>
-During germination, the tube cell elongates into a [[pollen tube]]. In the flower, the pollen tube then grows towards the [[ovule]] where it discharges the [[sperm]] produced in the pollen grain for fertilization. The germinated pollen grain with its two sperm cells is the mature male [[Gametophyte|microgametophyte]] of these plants.<ref name="Raven"/>
-=== Self-incompatibility ===
-{{Main|Self-incompatibility in plants}}
-Since most plants carry both male and female reproductive organs in their flowers, there is a high risk of self-pollination and thus [[inbreeding]]. Some plants use the control of pollen germination as a way to prevent this self-pollination. Germination and growth of the pollen tube involve molecular signaling between stigma and pollen. In [[self-incompatibility in plants]], the stigma of certain plants can molecularly recognize pollen from the same plant and prevent it from germinating.<ref name="Takayama">{{cite journal |author=Takayama S, Isogai A |title=Self-incompatibility in plants |journal=Annu Rev Plant Biol |volume=56 |issue= |pages=467–89 |year=2005 |pmid=15862104 |doi=10.1146/annurev.arplant.56.032604.144249}}</ref>
-== Spore germination ==
-Germination can also refer to the emergence of cells from [[resting spore]]s and the growth of [[sporeling]] [[hypha]]e or [[Thallus|thalli]] from spores in [[Fungus|fungi]], [[alga]]e and some plants.
-[[Conidia]] are asexual reproductive spores of fungi which germinate under specific conditions. A variety of cells can be formed from the germinating conidia. The most common are germ tubes which grow and develop into hyphae. Another type of cell is a conidial anastomosis tube (CAT); these differ from germ tubes in that they are thinner, shorter, lack branches, exhibit determinate growth and home toward each other. Each cell is of a tubular shape, but the conidial anastomosis tube forms a bridge that allows fusion between conidia.<ref>Roca M., M.G.; Davide, L.C.; Davide, L.M.; Mendes-Costa, M.C.; Schwan, R.F.; Wheals, A. 2004. Conidial anastomoses fusions between Colletotrichum species. Mycological Research. 108, 11: 1320-1326.</ref><ref>Roca, M.G.; Arlt, J., Jeffree, C.E.; Read, N.D. 2005. Cell biology of conidial anastomosis tubes in Neurospora crassa. Eukaryotic Cell 4: 911-919.</ref>
-=== Resting spores ===
-In [[resting spore]]s, germination involves cracking the thick cell wall of the dormant spore. For example, in [[zygomycete]]s the thick-walled zygosporangium cracks open and the [[zygospore]] inside gives rise to the emerging sporangiophore. In [[Slime mould|slime molds]], germination refers to the emergence of [[amoeboid]] cells from the hardened spore. After cracking the spore coat, further development involves cell division, but not necessarily the development of a multicellular organism (for example in the free-living amoebas of slime molds).<ref name="Raven"/>
-=== Zoospores ===
-In motile [[zoospore]]s, germination
-=== Ferns and mosses ===
-In [[plant]]s such as [[bryophyte]]s, [[fern]]s, and a few others, spores germinate into independent [[gametophyte]]s. In the bryophytes (e.g., [[moss]]es and [[Marchantiophyta|liverworts]]), spores germinate into [[protonema]]ta, similar to fungal hyphae, from which the gametophyte grows. In [[fern]]s, the gametophytes are small, heart-shaped [[Prothallium|prothalli]] that can often be found underneath a spore-shedding adult plant.<ref name="Raven"/>
-== See also ==
-*[[Lily Seed Germination Types]]
-*[[Seed testing]]
-*[[Seedling]]
-== References ==
-{{reflist}}
-==External links==
-{{wikibooks}}
-* [http://theseedsite.co.uk/seedsowing.html Sowing Seeds] A survey of seed sowing techniques.
-* ''Seed Germination: Theory and Practice'', Norman C. Deno, 139 Lenor Dr., State College PA 16801, USA. An extensive study of the germination rates of a huge variety of seeds under different experimental conditions, including temperature variation and chemical environment.
-* [http://www.youtube.com/watch?v=XTZih16DUB4&hd=1 Germination time-lapse] ~1 minuite HD video of mung bean seeds germinating over 10 days. Hosted on youtube.
-[[Category:Articles with inconsistent citation formats]]
-[[Category:Seeds]]
-[[Category:Plant morphology]]
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