Seed 37694 225310415 2008-07-13T00:54:08Z EncycloPetey 474828 [[WP:UNDO|Undid]] revision 225296198 by [[Special:Contributions/200.120.17.223|200.120.17.223]] ([[User talk:200.120.17.223|talk]]) - rm link to commerical site about seeds from one country {{otheruses}} [[Image:Capsicum0.jpg|thumb|A ripe red [[jalapeño]] cut open to show the seeds]] A '''seed''' {{Audio-IPA|en-us-seed.ogg|/ˈsiːd/}} (in some plants, referred to as a '''kernel''') is a small [[Plant embryogenesis|embryonic]] [[plant]] enclosed in a covering called the seed coat, usually with some [[Food storage|stored food]]. It is the product of the ripened [[ovule]] of [[gymnosperm]] and [[angiosperm]] plants which occurs after [[fertilization]] and some growth within the mother plant. The formation of the seed completes the process of [[reproduction]] in seed plants (started with the development of [[flower]]s and [[pollination]]), with the [[embryo]] developed from the zygote and the [[seed coat]] from the integuments of the ovule. Seeds have been an important development in the reproduction and spread of [[flowering plants]], relative to more primitive plants like [[moss]]es, [[fern]]s and [[marchantiophyta|liverwort]]s, which do not have seeds and use other means to propagate themselves. This can be seen by the success of seed plants (both gymnosperms and angiosperms) in dominating biological [[Ecological niche|niche]]s on land, from [[forest]]s to [[grassland]]s both in hot and cold [[climates]]. The term ''seed'' also has a general meaning that predates the above &mdash; anything that can be [[Sowing|sown]] i.e. "seed" [[potato]]es, "seeds" of [[maize|corn]] or [[sunflower seed|sunflower "seeds"]]. In the case of [[sunflower]] and corn "seeds", what is sown is the seed enclosed in a shell or hull, and the potato is a tuber. == Seed structure == [[Image:Avocado_seed_diagram-en.svg|thumb|250px|The parts of an [[avocado]] seed (a [[dicot]]), showing the seed coat, [[endosperm]], and [[embryo]].]] A typical seed includes three basic parts: (1) an [[embryo]], (2) a supply of nutrients for the embryo, and (3) a seed coat. The [[embryo]] is an immature [[plant]] from which a new plant will grow under proper conditions. The embryo has one [[cotyledon]] or seed leaf in [[monocotyledon]]s, two cotyledons in almost all [[dicotyledon]]s and two or more in gymnosperms. The [[radicle]] is the embryonic root. The plumule is the embryonic shoot. The embryonic stem above the point of attachment of the cotyledon(s) is the [[epicotyl]]. The embryonic stem below the point of attachment is the [[hypocotyl]]. Within the seed, there usually is a store of [[nutrient]]s for the [[seedling]] that will grow from the embryo. The form of the stored nutrition varies depending on the kind of plant. In angiosperms, the stored food begins as a tissue called the [[endosperm]], which is derived from the parent plant via [[double fertilization]]. The usually triploid endosperm is rich in [[Vegetable oil|oil]] or [[starch]] and [[protein]]. In gymnosperms, such as [[Pinophyta|conifer]]s, the food storage tissue is part of the female gametophyte, a haploid tissue. In some species, the embryo is embedded in the endosperm or female gametophyte, which the seedling will use upon [[germination]]. In others, the endosperm is absorbed by the embryo as the latter grows within the developing seed, and the cotyledons of the embryo become filled with this stored food. At maturity, seeds of these species have no endosperm and are termed exalbuminous seeds. Some exalbuminous seeds are [[bean]], [[pea]], [[oak]], [[walnut]], [[Squash (vegetable)|squash]], [[sunflower]], and [[radish]]. Seeds with an endosperm at maturity are termed albuminous seeds. Most monocots (e.g. [[Poaceae|grasses]] and [[Arecaceae|palms]]) and many dicots (e.g. [[brazil nut]] and [[castor bean]]) have albuminous seeds. All gymnosperm seeds are albuminous. The seed coat (or ''testa'') develops from the tissue, the integument, originally surrounding the ovule. The seed coat in the mature seed can be a paper-thin layer (e.g. [[peanut]]) or something more substantial (e.g. thick and hard in [[honey locust]] and [[coconut]]). The seed coat helps protect the embryo from mechanical injury and from drying out. In addition to the three basic seed parts, some seeds have an appendage on the seed coat such an [[aril]] (as in [[Taxus|yew]] and [[nutmeg]]) or an [[elaiosome]] (as in [[Corydalis]]) or hairs (as in [[cotton]]). There may also be a scar on the seed coat, called the ''hilum''; it is where the seed was attached to the ovary wall by the [[ovule|funiculus]]. == Seed production == [[Image:ElmBlossom.jpg|thumb|240px|Immature [[Elm]] seeds.]] Seeds are produced in several related groups of plants, and their manner of production distinguishes the [[angiosperm]]s ("enclosed seeds") from the [[gymnosperm]]s ("naked seeds"). Angiosperm seeds are produced in a hard or fleshy (or with layers of both) structure called a [[fruit]] that encloses the seeds, hence the name. In gymnosperms, no special structure develops to enclose the seeds, which begin their development "naked" on the bracts of cones. However, the seeds do become covered by the [[Conifer cone|cone]] scales as they develop in some species of [[conifer]]. === Kinds of seeds === There are a number of modifications to seeds by different groups of plants. One example is that of the so-called ''[[Drupe|stone]]'' fruits (such as the [[peach]]), where a hardened fruit layer ( the '''endocarp''') surrounds the actual seed and is fused to it. Many structures commonly referred to as "seeds" are actually dry [[fruit]]s. [[Sunflower]] seeds are sold commercially while still enclosed within the hard wall of the fruit, which must be split open to reach the seed. === Seed development === [[Image:Ginkgo embryo and gametophyte.jpg|thumb|180px|The inside of a ''[[Ginkgo]]'' seed, showing a well-developed embryo, nutritive tissue (mega[[gametophyte]]), and a bit of the surrounding seed coat.]] [[Image:Budowa nasienia-dwuliscienne.png|thumb|180px|Diagram of the internal structure of a [[dicot]] seed and embryo. (a) seed coat, (b) [[endosperm]], (c) [[cotyledon]], (d) [[hypocotyl]].]] The seed, which is an embryo with two points of growth (one of which forms the stems the other the roots) is enclosed in a seed coat with some food reserves. Angiosperm seeds consist of three genetically distinct constituents: (1) the embryo formed from the zygote, (2) the endosperm, which is normally triploid, (3) the seed coat from tissue derived from the maternal tissue of the ovule. In angiosperms, the process of seed development begins with [[double fertilization]] and involves the fusion of the egg and sperm nuclei into a zygote. The second part of this process is the fusion of the polar nuclei with a second sperm cell nucleus, thus forming a primary [[endosperm]]. Right after fertilization the zygote is mostly inactive but the primary endosperm divides rapidly to form the endosperm tissue. This tissue becomes the food that the young plant will consume until the roots have developed after germination or it develops into a hard seed coat. The seed coat forms from the two integuments or outer layers of cells of the ovule, which derive from tissue from the mother plant, the inner integument forms the [[tegmen]] and the outer forms the testa. When the seed coat forms from only one layer it is also called the testa, though not all such testa are [[homologous]] from one species to the next. In gymnosperms, the two sperm cells transferred from the pollen do not develop seed by double fertilization but instead only one sperm fertilizes the egg while the other is not used. The seed is composed of the embryo (the result of fertilization) and tissue from the mother plant, which also form a cone around the seed in coniferous plants like [[Pine]] and [[Spruce]]. The ovules after fertilization develop into the seeds; the main parts of the ovule are the [[funicle]]; which attaches the ovule to the placenta, the [[nucellus]]; the main region of the ovule were the embryo sac develops, the [[micropyle]]; A small pore or opening in the ovule where the pollen tube usually enters during the process of fertilization, and the [[chalaza]]; the base of the ovule opposite the micropyle, where integument and nucellus are joined together.<ref>Kigel, Jaime, and Gad Galili. 1995. ''Seed development and germination. Books in soils, plants, and the environment''. New York: M. Dekker.ISBN 0824792297. Chapter one.</ref> The shape of the ovules as they develop often affects the finale shape of the seeds. Plants generally produce ovules of four shapes: the most common shape is called anatropous, with a curved shape. Orthotropous ovules are straight with all the parts of the ovule lined up in a long row producing an uncurved seed. Campylotropous ovules have a curved embryo sac often giving the seed a tight “c” shape. The last ovule shape is called amphitropous, where the ovule is partly inverted and turned back 90 degrees on its stalk or funicle. In the majority of flowering plants the zygotes first division is transversely orientated in regards to the long axis and this establishes the polarity of the embryo. The upper or chalazal pole becomes the main area of growth of the embryo, while the lower or micropylar pole produces the stalk-like suspensor that attaches to the micropyle. The suspensor absorbs and manufacturers nutrients from the endosperm that are utilized during the embryos growth.<ref>Raven, Peter H., Ray Franklin Evert, and Helena Curtis. 1981. ''Biology of plants''. New York, N.Y.: Worth Publishers. page 410.</ref> The embryo is composed of different parts; the '''epicotyle''' will grow into the shoot, the '''radicle''' grows into the primary root, the '''hypocotyl''' connects the epicotyle and the radicle, the '''cotyledons''' form the seed leaves, the '''testa''' or seed coat forms the outer covering of the seed. Monocotyledonous plants like corn, have other structures; instead of the hypocotyle-epicotyle, it has a '''coleoptile''' that forms the first leaf and connects to the '''coleorhiza''' that connects to the primary root and [[adventitious]] roots form from the sides. The seeds of corn are constructed with these structures; pericarp, scutellum (single large cotyledon) that absorbs nutrients from the endosperm, endosperm, plumule, radicle, coleoptile and coleorhiza - these last two structures are sheath-like and enclose the plumule and radicle, acting as a protective covering. The testa or seed coats of both monocots and dicots are often marked with patterns and textured markings, or have wings or tufts of hair. === Seed size and seed set === Seeds are very diverse in size. The dust-like orchid seeds are the smallest with about one million seeds per gram, they are often embryonic seeds with immature embryos and no significant energy reserves. Orchids and a few other groups of plants are [[myco-heterotrophy|myco-heterotrophs]] which depend on [[mycorrhizal fungi]] for nutrition during germination and the early growth of the seedling. Some terrestrial Orchid seedlings, in fact, spend the first few years of their life deriving energy from the fungus and do not produce green leaves.<ref>Smith, Welby R. 1993. ''Orchids of Minnesota''. Minneapolis: University of Minnesota Press. Page 8.</ref> At over 20 kg, the largest seed is the [[coco de mer]]. Plants that produce smaller seeds can generate many more seeds per flower, while plants with larger seeds invest more resources into those seeds and normally produce fewer seeds. Small seeds are quicker to ripen and can be dispersed sooner, so fall blooming plants often have small seeds. Many annual plants produce great quantities of smaller seeds; this helps to ensure that at least a few will end in a favorable place for growth. Herbaceous perennials and woody plants often have larger seeds, they can produce seeds over many years, and larger seeds have more energy reserves for germination and seedling growth and produce larger, more established seedlings after germination.<ref>http://www.springerlink.com/content/1027t86224633171/</ref><ref>http://cat.inist.fr/?aModele=afficheN&cpsidt=2706202</ref> == Seed functions == Seeds serve several functions for the plants that produce them. Key among these functions are nourishment of the [[embryo]], [[biological dispersal|dispersal]] to a new location, and [[dormancy]] during unfavorable conditions. Seeds fundamentally are a means of reproduction and most seeds are the product of [[sexual reproduction]] which produces a remixing of genetic material and [[phenotype]] variability that [[natural selection]] acts on. ===Embryo nourishment=== Seeds protect and nourish the embryo or baby plant. Seeds usually give a seedling a faster start than a sporling from a spore gets because of the larger food reserves in the seed. ===Seed dispersal=== {{main|Biological dispersal}} Unlike animals, plants are limited in their ability to seek out favorable conditions for life and growth. As a consequence, plants have evolved many ways to [[Biological dispersal|disperse]] their offspring by dispersing their seeds (see also [[vegetative reproduction]]). A seed must somehow "arrive" at a location and be there at a time favorable for germination and growth. When the fruits open and release their seeds in a regular way, it is called dehiscent, which is often distinctive for related groups of plants, these fruits include; Capsules, follicles, legumes, silicles and siliques. When fruits do not open and release their seeds in a regular fashion they are called indehiscent, which include these fruits; Achenes, caryopsis, nuts, samaras, and utricles.<ref>Jones, Samuel B., and Arlene E. Luchsinger. 1979. ''Plant systematics. McGraw-Hill series in organismic biology''. New York: McGraw-Hill. Page 195.</ref> Seed dispersal is seen most obviously in fruits; however many seeds aid in their own dispersal. Some kinds of seeds are dispersed while still inside a [[fruit]] or [[conifer cone|cone]], which later opens or disintegrates to release the seeds. Other seeds are expelled or released from the fruit prior to dispersal. For example, [[milkweed]]s produce a fruit type, known as a ''[[Follicle (fruit)|follicle]]'',<ref name="Cronquist 1981">{{cite book | last= Cronquist | first= Arthur | year=1981 | title=An Integrated System of Classification of Flowering Plants | pages=882 | location= New York | publisher= Columbia University Press | id=ISBN 0-231-03880-1 }}</ref> that splits open along one side to release the seeds. [[Iris (plant)|Iris]] [[Capsule (fruit)|capsules]] split into three "valves" to release their seeds.<ref name="Stern 1991">{{cite book | last= Stern | first= Kingsley R. | year=1991 | title=Introductory Plant Biology | edition = 5th | pages=131 | location= Dubuque, IA | publisher= Wm. C. Brown Publishers | id=ISBN 0-697-09947-4 }}</ref> ====By wind ([[anemochory]])==== [[image:Photos-photos_1088103921_Floating.jpg|thumb|240px|Dandelion seeds ([[achene]]s) can be carried long distances by the wind.]] * Many seeds (e.g. [[maple]], [[pine]]) have a wing that aids in wind dispersal. * The dustlike seeds of [[orchid]]s are carried efficiently by the wind. * Some seeds, (e.g. [[dandelion]], [[milkweed]], [[poplar]]) have hairs that aid in wind dispersal. ====By water ([[hydrochory]])==== * Some plants, such as ''[[Mucuna]]'' and ''[[Dioclea]]'', produce buoyant seeds termed sea-beans or drift seeds because they float in rivers to the oceans and wash up on beaches.<ref>[http://www.seabean.com/ www.seabean.com - Sea-Beans and Drift Seeds<!-- Bot generated title -->]</ref> ====By animals ([[zoochory]])==== * Seeds ([[burr (fruit)|burr]]s) with barbs or hooks (e.g. [[acaena]], [[burdock]], [[Rumex|dock]] which attach to animal fur or feathers, and then drop off later. * Seeds with a fleshy covering (e.g. [[apple]], [[cherry]], [[juniper]]) are eaten by animals ([[bird]]s, [[mammal]]s) which then disperse these seeds in their [[faeces|droppings]]. * Seeds ([[nut (fruit)|nuts]]) which are an attractive long-term storable food resource for animals (e.g. [[acorn]]s, [[hazel]]nut, [[walnut]]); the seeds are stored some distance from the parent plant, and some escape being eaten if the animal forgets them. '''[[Myrmecochory]]''' is the dispersal of seeds by [[ant]]s. Foraging ants disperse seeds which have appendages called [[elaiosome]]s<ref>Marinelli, J. (1999) "Ants - The astonishing intimacy between ants & plants." ''Plants & Gardens News'' '''14''' (1). [http://www.bbg.org/gar2/topics/wildlife/1999sp_ants.html]</ref> (e.g. [[bloodroot]], [[trillium]]s, [[Acacia]]s, and many species of [[Proteaceae]]). Elaiosomes are soft, fleshy structures that contain nutrients for animals that eat them. The ants carry such seeds back to their nest, where the elaiosomes are eaten. The remainder of the seed, which is hard and inedible to the ants, then germinates either within the nest or at a removal site where the seed has been discarded by the ants.<ref name="Ricklefs 1993">Ricklefs, Robert E. (1993) ''The Economy of Nature'', 3rd ed., p.396. (New York: W. H. Freeman). ISBN 0-7167-2409-X.</ref> This dispersal relationship is an example of [[mutualism]], since the plants depend upon the ants to disperse seeds, while the ants depend upon the plants seeds for food. As a result, a drop in numbers of one partner can reduce success of the other. In [[South Africa]], the [[Argentine ant]] (''Linepithema humile'') has [[invasive species|invaded]] and displaced native species of ants. Unlike the native ant species, Argentine ants do not collect the seeds of ''[[Mimetes cucullatus]]'' or eat the elaiosomes. In areas where these ants have invaded, the numbers of ''Mimetes'' [[seedling]]s have dropped.<ref>{{cite journal | author = Bond, W. J. | coauthors = P. Slingsby | year=1984 | title = Collapse of an ant-plant mutualism: The Argentine ant, ''Iridomyrmex humilis'' and myrmecochorous Proteaceae | journal = Ecology | volume=65 | pages=1031–1037 | doi = 10.2307/1938311 <!--Retrieved from CrossRef by DOI bot-->}}</ref> ===Seed dormancy and protection=== {{further|[[Seed hibernation]]}} One important function of most seeds is delaying germination, which allows time for dispersal and prevents germination of all the seeds at one time. The staggering of germination safeguards some seeds and seedlings from suffering damage or death from short periods of bad weather or from transient herbivores, it also allows some to germinate when competition from other plants for light and water might be less. Many species of plants have seeds that germinate over many months or years, and some seeds can remain in the soil seed bank for more than 50 years before germination. Some seed have a very long viability period, with the oldest documented germinating seed carbon dated to be 2000 years old.<ref>RANDOLPH E. SCHMID, '[http://news.yahoo.com/s/ap/20080612/ap_on_sc/sci_ancient_tree Tree from 2,000-year-old seed is doing well]'. AP, Jun 12, 2008</ref> [[Seed dormancy]] is defined as a seed failing to germinate under environmental conditions optimal for germination, normally when the environment is at a suitable temperature with proper soil moisture. Induced dormancy or seed quiescence occurs when a seed fails to germinate because the external environmental conditions are inappropriate for germination, mostly in response to being too cold or hot, or too dry. True dormancy or innate dormancy is caused by conditions within the seed that prevent germination under normally ideal conditions. Often seed dormancy is divided into four major categories: exogenous; endogenous; combinational; and secondary. Exogenous dormancy is caused by conditions outside the embryo including: *'''Hard seed coats''' or physical dormancy occurs when seeds are [[Permeability (fluid)|impermeable]] to water or the exchange of gases. In some seeds the seed coat physically prevents the seedling from growing. *'''Chemical dormancy''' includes growth regulators etc. Endogenous dormancy is caused by conditions within the embryo itself, including: *'''Immature embryos''' where some plants release their seeds before the tissues of the embryos have fully differentiated, and the seeds ripen after they take in water while on the ground, germination can be delayed from a few weeks to a few months. *'''Morphological dormancy''' where seeds have fully differentiated embryos that need to grow more before seed germination, the embryos are not yet fully developed. *'''Morphophysiological dormancy''' seeds with underdeveloped embryos, and in addition have physiological components to dormancy. These seeds therefore require a dormancy-breaking treatments as well as a period of time to develop fully grown embryos. *'''Physiological dormancy''' prevents seed germination until the chemical inhibitors are broken down or are no longer produced by the seed, often physiological dormancy is broken by a period of cool moist conditions, normally below (+4C) 39F, or in the case of many species in ''[[Ranunculaceae]]'' and a few others,(-5C) 24F. Other chemicals that prevent germination are washed out of the seeds by rainwater or snow melt. [[Abscisic acid]] is usually the growth inhibitor in seeds and its production can be affected by light. Some plants like [[Peony]] species have multiple types of physiological dormancy, one affects radical growth while the other affects shoot growth. **'''Drying'''; some plants including a number of grasses and those from seasonally arid regions need a period of drying before they will germinate, the seeds are released but need to have a lower moister content before germination can begin. If the seeds remain moist after dispersal, germination can be delayed for many months or even years. Many herbaceous plants from temperate climate zones have physiological dormancy that disappears with drying of the seeds. Other species will germinate after dispersal only under very narrow temperature ranges, but as the seeds dry they are able to germinate over a wider temperature range.<ref>International Workshop on Seeds, and G. Nicolas. 2003. ''The biology of seeds recent research advances : proceedings of the Seventh International Workshop on Seeds, Salamanca, Spain 2002''. Wallingford, Oxon, UK: CABI Pub. Page 113.</ref> **'''Photodormancy''' or light sensitivity affects germination of some seeds. These photoblastic seeds need a period of darkness or light to germinate. In species with thin seed coats, [[light]] may be able to penetrate into the dormant embryo. The presence of light or the absence of light may trigger the germination process, inhibiting germination in some seeds buried too deeply or in others not buried in the soil. **'''Thermodormancy''' is seed sensitivity to heat or cold. Some seeds including cocklebur and amaranth germinate only at high temperatures (30C or 86F) many plants that have seed that germinate in early to mid summer have thermodormancy and germinate only when the soil temperature is warm. Other seeds need cool soils to germinate, while others like celery are inhibited when soil temperatures are too warm. Often thermodormancy requirements disappear as the seed ages or dries. Combinational dormancy also called double dormancy. Many seeds have more than one type of dormancy,<ref>[http://www.seedbiology.de/dormancy.asp The Seed Biology Place - Seed Dormancy<!-- Bot generated title -->]</ref> some ''[[Iris (plant)|Iris]]'' species have both hard impermeable seeds coats and physiological dormancy. Secondary dormancy is caused by conditions after the seed has been dispersed and occurs in some seeds when non-dormant seed is exposed to conditions that are not favorable to germination, very often high temperatures. The mechanisms of secondary dormancy are not yet fully understood but might involve the loss of sensitivity in receptors in the plasma membrane.<ref>Bewley, J. Derek, and Michael Black. 1994. ''Seeds physiology of development and germination. The language of science''. New York: Plenum Press. page 230.</ref> Many garden plants have seeds that will germinate readily as soon as they have water and are warm enough, though their wild ancestors may have had dormancy, these cultivated plants lack seed dormancy. After many generations of selective pressure by plant breeders and gardeners dormancy has been selected out. For [[annual plant|annuals]], seeds are a way for the species to survive dry or cold seasons. Ephemeral plants are usually annuals that can go from seed to seed in as few as six weeks.<ref>Patten, D.T. 1978. Productivity and production efficiency of an Upper Sonoran Desert ephemeral community. ''American Journal of Botany'' 65: 891-895.</ref> Not all seeds undergo a period of dormancy. Seeds of some [[mangrove]]s are viviparous, they begin to germinate while still attached to the parent. The large, heavy root allows the seed to penetrate into the ground when it falls. ==Seed germination== [[Image:Sunflower seedlings.jpg|thumb|180px|Germinating [[sunflower]] seedlings.]] {{main|Seedling|Germination}} Seed germination is the process of growth of the embryo into a functional plant. It involves the reactivation of the metabolic pathways that lead to growth and the emergence of the radicle or seed root and plumule or shoot. Three fundamental conditions must exist before germination can occur. (1) The embryo must be alive, called seed viability. (2) Any dormancy requirements that prevent germination must be over come. (3) The proper environmental conditions must exist for germination. Seed viability determines the percentage of possible seed germination and is affected by a number of different conditions. Some plants do not produce seeds that have functional complete embryos or the seed may have no embryo at all, often called empty seeds. Predators and pathogens can damage or kill the seed while it is still in the fruit or after it is dispersed. Environmental conditions like flooding or heat can kill the seed before or during germination. The age of the seed affects its health and germination ability, since the seed has a living embryo, over time cells die and cannot be replaced. Some seeds can live for a long time before germination, while others can only survive for a short period after dispersal before they die. '''Seed vigor''' is a measure of the quality of seed, and involves the viability of the seed, the germination percentage, germination rate and the strength of the seedlings produced.<ref>[http://extension.osu.edu/~seedsci/svvt01.html Seed Vigor and Vigor Tests<!-- Bot generated title -->]</ref> The '''germination percentage''' is simply the proportion of seeds that germinate from all seeds subject to the right conditions for growth. The '''germination rate''' is the length of time it takes for the seeds to germinate. Germination percentages and rates are affected by seed viability, dormancy and environmental effects that impact on the seed and seedling. In agriculture and horticulture quality seeds have high viability, measured by germination percentage plus the rate of germination. This is given as a percent of germination over a certain amount of time, 90% germination in 20 days, for example. 'Dormancy' is covered above; many plants produce seeds with varying degrees of dormancy, and different seeds from the same fruit can have different degrees of dormancy.<ref>International Seed Testing Association. 1973. ISSN 0251-0952. Pages 120-21.''Seed science and technology''. Wageningen?: International Seed Testing Association.</ref> It's possible to have seeds with no dormancy if they are dispersed right away and do not dry (if the seeds dry they go into physiological dormancy). There is great variation amongst plants and a dormant seed is still a viable seed even though the germination rate might be very low. Environmental conditions effecting seed germination include; water, oxygen, temperature and light. Three distinct phases of seed germination occur: water imbibition; lag phase; and [[radicle]] emergence. In order for the seed coat to split, the embryo must imbibe (soak up water), which causes it to swell, splitting the seed coat. However, the nature of the seed coat determines how rapidly water can penetrate and subsequently initiate [[germination]]. The rate of imbibition is dependent on the permeability of the seed coat, amount of water in the environment and the area of contact the seed has to the source of water. For some seeds, imbibing too much water too quickly can kill the seed. For some seeds, once water is imbibed the germination process cannot be stopped, and if the seed dries out again it is fatal. Other species have seeds that can imbibe and lose water a few times without causing ill effects to the seed, and drying can cause secondary dormancy. ===Inducing germination=== A number of different strategies are used by gardeners and horticulturists to break seed dormancy. '''Scarification''' which allows water and gases to penetrate into the seed, include methods that physical break the hard seed coats or soften them by chemicals. Means of scarification include soaking in hot water or poking holes in the seed with a pin or rubbing them on sandpaper or cracking with a press or hammer. Soaking the seeds in solvents or acids is also effective for many seeds. Sometimes fruits are harvested while the seeds are still immature and the seed coat is not fully developed and sown right away before the seed coat become impermeable. Under natural conditions seed coats are worn down by rodents chewing on the seed, the seeds rubbing against rocks (seeds are moved by the wind or water currents), by undergoing freezing and thawing of surface water, or passing through an animal's digestive tract. In the latter case, the seed coat protects the seed from [[digestion]], while often weakening the seed coat such that the embryo is ready to sprout when it gets deposited (along with a bit of fertilizer) far from the parent plant. [[Microorganism]]s are often effective in breaking down hard seed coats and are sometimes used by people as a treatment, the seeds are stored in a moist warm sandy medium for several months under non-sterile conditions. '''Stratification''' also called moist-chilling is a method to break down physiological dormancy and involves the addition of moisture to the seeds so they imbibe water and then the seeds are subject to a period of moist chilling to after-ripen the embryo. Sowing outside in late summer and fall and allowing to overwinter outside under cool conditions is an effective way to stratify seeds, some seeds respond more favorably to periods of osculating temperatures which are part of the natural environment. '''Leaching''' or the soaking in water removes chemical inhibitors in some seeds that prevent germination. [[Rain]] and melting [[snow]] naturally accomplish this task. For seeds planted in gardens, running water is best - if soaked in a container, 12 to 24 hours of soaking is sufficient. Soaking longer, especially in stagnant water that is not changed, can result in oxygen starvation and seed death. Seeds with hard seed coats can be soaked in hot water to break open the impermeable cell layers that prevent water intake. Other methods used to assist in the germination of seeds that have dormancy include prechilling, predrying, daily alternation of temperature, light exposure, potassium nitrate, the use of plant growth regulators like gibberellins, cytokinins, ethylene, thiourea, sodium hypochlorite plus others.<ref>Hartmann, Hudson Thomas, and Dale E. Kester. 1983. ''Plant propagation principles and practices''. Englewood Cliffs, N.J.: Prentice-Hall. ISBN 0136810071. Pages 175-77.</ref> Some seeds germinate best after a fire, for some seeds fire crakes hard seed coats while in other seeds chemical dormancy is broken in reaction to the presence of smoke, liquid smoke is often used by gardeners to assist in the germination of these species.<ref>http://www.sciencemag.org/cgi/content/abstract/276/5316/1248</ref> ==Origin and evolution== The origin of seed plants is a problem that still remains unsolved. However, more and more data tends to place this origin in the middle [[Devonian]]. The description in 2004 of the proto-seed ''Runcaria heinzelinii'' in the [[Givetian]] of [[Belgium]] is an indication of that ancient origin of seed-plants. As with modern ferns, most land plants before this time reproduced by sending spores into the air, that would land and become whole new plants. The first "true" seeds are described from the upper Devonian, which is probably the theater of their true first evolutionary radiation. The seed plants progressively became one of the major elements of nearly all ecosystems. ==Economic importance== [[Image:Phaseolus vulgaris seed.jpg|240px|thumb|A variety of [[legume|bean]] seeds.]] ===Edible seeds=== {{further|[[List of edible seeds]]}} Many seeds are [[List of edible seeds|edible]] and the majority of human calories comes from seeds, especially from [[cereal]]s, [[legume]]s and [[Nut (fruit)|nut]]s. Seeds also provide most [[cooking oil]]s, many [[beverage]]s and [[spice]]s and some important [[food additive]]s. In different seeds the [[Embryo#Embryos of plants and animals|seed embryo]] or the [[endosperm]] dominates and provides most of the [[nutrient]]s. The storage [[protein]]s of the embryo and endosperm differ in their [[amino acid]] content and physical properties. For example the [[gluten]] of wheat, important in providing the [[Elasticity (physics)|elastic]] property to bread [[dough]] is strictly an endosperm protein. Seeds are used to propagate many crops such as cereals, legumes, [[forestry|forest trees]], [[turfgrass]]es and [[pasture]] grasses. Seeds are also eaten by [[animal]]s, and are fed to [[livestock]]. Many seeds are used as [[birdseed]]. ===Poison and food safety=== While some seeds are considered by some as healthy to eat, other seeds may be harmful or poisonous,<ref>Chia Joo Suan, "[http://kuali.com/news/story.asp?file=/2006/7/5/kuali/14689925&sec=Kuali Seeds of Doubt: Food Safety]"</ref> Plants and seeds often contain [[chemical compounds]] to discourage [[herbivores]] and [[seed predation|seed predators]]. In some cases, these compounds simply taste bad (such as in [[Mustard (condiment)|mustard]]), but other compounds are toxic, or breakdown into toxic compounds within the [[digestive system]]. Children, being smaller than adults, are more susceptible to poisoning or death by plants and seeds.<ref>Clelland, Mike. "[http://www.healthychild.net/articles/sf21plants.html Poisonous Plants and Seeds]", ''Healthy Child Care''</ref> One should be satisfied with reliable food safety information before choosing to eat any particular seeds. An infamously deadly poison, [[ricin]], comes from seeds of the [[castor bean]]. Reported lethal doses are anywhere from two to eight seeds,<ref>[http://plantanswers.tamu.edu/publications/poison/poison.html Poisonous Plants]</ref><ref>[http://www.ncbi.nlm.nih.gov/sites/entrez?itool=AbstractPlus&db=pubmed&cmd=Retrieve&dopt=abstractplus&list_uids=3964368 Wedin GP, Neal JS, Everson GW, Krenzelok EP. Castor bean poisoning.]</ref> though only a few deaths have been reported when castor beans have been ingested by animals.<ref>[http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=10825094&ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVAbstractPlus Albretsen JC, Gwaltney-Brant SM, Khan SA. Evaluation of castor bean toxicosis in dogs: 98 cases.]</ref> In addition, seeds containing [[amygdalin]]; [[apple]], [[apricot]], [[bitter almond]],<ref name="almond">[http://www.drugs.com/npp/almond-almond-oil.html Almond/Almond Oil]</ref> [[peach]], [[plum]], [[cherry]], [[quince]], and others, when consumed in significant amounts, may result in cyanide toxicity<ref name="almond"/>.<ref>[http://www.washingtonpost.com/wp-dyn/articles/A46703-2005Jan4.html Wolke, RL. ''Seeds of Anxiety'' Washington Post January 5, 2005]</ref> Other seeds than contain poisons include [[annona]], [[cotton]], [[custard apple]], [[datura]], uncooked [[durian]], [[golden chain]], [[Horse-chestnut (tree)|horse-chestnut]], [[Delphinium|larkspur]], [[locoweed]], [[lychee]], [[nectarine]], [[rambutan]], [[rosary pea]], [[sour sop]], [[sugar apple]], [[wisteria]], and [[Taxus|yew]].<ref>[http://plantanswers.tamu.edu/publications/poison/poison.html Poisonous plants]</ref><ref>[http://kuali.com/news/story.asp?file=/2006/7/5/kuali/14689925&sec=Kuali Chia Joo Suan Food Safety: Seeds of doubt]</ref> Another seed poison is [[strychnine]]. The seeds of many legumes, including the common bean (''[[Phaseolus vulgaris]]'') contain proteins called [[lectins]] which can cause gastric distress if the beans are eaten without [[cooking]]. The common bean and many others, including the [[soybean]], also contain [[trypsin inhibitors]] which interfere with the action of the digestive enzyme [[trypsin]]. Normal cooking processes degrade lectins and trypsin inhibitors to harmless forms.<ref>[http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2621.1990.tb06789.x?cookieSet=1&journalCode=jfds N.V. DHURANDHAR, K.C. CHANG (1990) Effect of Cooking on Firmness, Trypsin Inhibitors, Lectins and Cystine/Cysteine content of Navy and Red Kidney Beans (Phaseolus vulgaris) Journal of Food Science 55 (2), 470–474.]</ref> ===Other uses=== [[Image:Omega-Nutrition-Coconut-Oil-3060.jpg|thumb|240px|[[Linseed oil|Flax seed oil]] (in bottles) and [[coconut oil]] (in jars in the middle).]] The world's most important clothing [[fiber]] grows attached to [[cotton]] seed. Other seed fibers are from [[kapok]] and [[milkweed]]. Many important nonfood oils are extracted from seeds. [[Linseed oil]] is used in paints. Oil from [[jojoba]] and [[crambe]] are similar to [[whale oil]]. Seeds are the source of some medicines including [[castor oil]], [[tea tree oil]] and the discredited cancer drug, [[Amygdalin|Laetrile]]. Many seeds have been used as [[bead]]s in necklaces and rosaries including [[Job's tears]], [[Chinaberry]] and [[Abrus precatorius|rosary pea]]. However, the latter two are also poisonous. Other seed uses include: * Seeds once used as weights for [[Weighing scale|balance]]s. * Seeds used as toys by children, such as for the game [[conker]]. * Resin from ''[[Clusia]] rosea'' seeds used to caulk boats. * [[Nematicide]] from [[milkweed]] seeds. * [[Cottonseed meal]] used as animal feed and [[fertilizer]]. ==Trivia== [[Image:Female coco de mer seed.jpg|thumb|200px|The massive [[fruit]] of the [[coco de mer]].]] * The [[Oldest viable seed|oldest viable]] [[carbon-14]]-dated seed that has grown into a plant was a [[Judean date palm]] seed about 2,000 years old, recovered from excavations at [[Herod the Great]]'s palace on [[Masada]] in [[Israel]]. It was germinated in 2005. <ref>Roach, John. (2005) "[http://news.nationalgeographic.com/news/2005/11/1122_051122_old_seed.html 2,000-Year-Old Seed Sprouts, Sapling Is Thriving]", ''National Geographic News'', 22 November.</ref> * The largest seed is produced by the [[coco de mer]], or "double coconut palm", ''Lodoicea maldivica''. The entire [[fruit]] may weigh up to 23 kilograms (50 pounds) and usually contains a single seed.<ref>Corner, E. J. H. (1966) ''The Natural History of Palms'', p313-314. (Berkeley, CA: University of California Press).</ref> * The earliest [[fossil]] seeds are around 365 million years old from the [[Famennian|Late]] [[Devonian]] of [[West Virginia]]. The seeds are preserved immature [[ovule]]s of the [[plant]] ''[[Elkinsia polymorpha]]''.<ref>Taylor, Thomas N. & Edith L. Taylor. 1993 ''The Biology and Evolution of Fossil Plants'', page 466. (Englewood Cliffs, NJ: Prentice Hall). ISBN 0-13-651589-4.</ref> == See also == {{Portalpar|Biology}} * [[Biological dispersal]] * [[Germination]] * [[List of edible seeds]] * [[Recalcitrant seed]] * [[Seed company]] * [[Seed orchard]] * [[Seed predation]] * [[Seedbed]] * [[Seedling]] * [[Stratification (botany)|Stratification]] == References == {{reflist|2}} ==External links== {{Commons|Seed}} {{wiktionary|seed}} * [http://www.seedlab.co.nz/NAMESEED.HTM List of Common Botanical Seed Names] * [http://theseedsite.co.uk/ The Seed Site]: collecting, storing, sowing, germinating, and exchanging seeds, with pictures of seeds, seedpods and seedlings. * [http://www.seedbiology.de/index.html The Seed Biology Place] seed structure, dormany, evolution, ecology, etc. * [http://www.alpine-plants-jp.com/himitunohanazono/index_himitunohanazono_0.htm Flavon's Secret Flower Garden] - Pictures of Japanese plant seeds, fruits and etc. * [http://www.kew.org/msbp/ The Millennium Seed Bank Project] Kew Garden's ambitious preservation project * [http://www.regjeringen.no/en/dep/lmd/campain/svalbard-global-seed-vault.html?id=462220 The Svalbard Global Seed Vault] - a backup facility for the world's seed banks {{-}} {{Botany}} [[Category:Agronomy]] [[Category:Forestry]] [[Category:Horticulture]] [[Category:Plant morphology]] [[Category:Plant sexuality]] [[Category:Plant reproduction]] [[ar:بذرة]] [[an:Simién]] [[ast:Semiente]] [[ay:Jatha]] [[zh-min-nan:Chí]] [[bg:Семе]] [[ca:Llavor]] [[cs:Semeno]] [[da:Frø (plantedel)]] [[de:Same (Pflanze)]] [[es:Semilla]] [[eo:Semo]] [[fr:Graine]] [[ko:씨]] [[hi:बीज]] [[hr:Sjeme]] [[id:Biji]] [[it:Seme]] [[he:זרע (בוטניקה)]] [[lt:Sėkla]] [[hu:Mag]] [[nl:Zaad (plant)]] [[nds-nl:Zaod (plaante)]] [[ja:種子]] [[no:Frø]] [[nn:Frø]] [[pl:Nasienie (botanika)]] [[pt:Semente]] [[ro:Sămânţă]] [[qu:Muru]] [[ru:Семя (ботаника)]] [[scn:Simenta]] [[simple:Seed]] [[sl:Seme]] [[sr:Семе]] [[sh:Sjeme]] [[su:Siki]] [[fi:Siemen]] [[sv:Frö]] [[te:విత్తనము]] [[tr:Tohum]] [[uk:Насіння]] [[vec:Sémi]] [[zh:種子]]