| Line 1: |
Line 1: |
| − | [[Image:Macro 1 bg 122703.jpg|thumb|A ripe red [[jalapeño]] cut open to show the seeds]] | + | [[Image:Upload.png|thumb|[[Special:Upload|Upload image!]]]] |
| − | {{otheruses}}
| + | The ripened [[ovule]]; the essential part is the [[embryo]], and this is contained within integuments.{{SCH}} |
| − | A '''seed''' is a small [[Plant embryogenesis|embryonic]] [[plant]] enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened [[ovule]] of [[gymnosperm]] and [[angiosperm]] plants which occurs after [[fertilization]] and some growth within the motherplant. 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.
| |
| | | | |
| − | This process starts with [[double fertilization]] in angiosperms and it 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, 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. 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]].
| + | {{glossary}} |
| − | | |
| − | The new seed is formed in plant structures called [[fruit]]s in angiosperms.
| |
| − | | |
| − | '''Seed''' also has a general meaning that predates the above - any thing that can be [[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 root or stem depending on what is being sowed.
| |
| − | | |
| − | 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]].
| |
| − |
| |
| − | == Seed structure ==
| |
| − | A seed contains the '''[[embryo]]''' from which a new plant will grow under proper conditions. Seeds also usually contain a supply of stored energy and is wrapped in the '''seed coat''' or testa. Seeds are very diverse in size. The dust-like orchid seeds are the smallest with about one million seeds per gram. Embryotic seeds have immature embryos and no significant energy reserves. They are [[myco-heterotrophy|myco-heterotrophs]], depending on [[mycorrhizal fungi]] for nutrition during germination. At over 20 kg, the largest seed is the [[coco de mer]].
| |
| − | | |
| − | 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]].
| |
| − | | |
| − | 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 wi
| |
| − | ll 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 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.
| |
| − | | |
| − | The seeds of angiosperms are contained in a hard or fleshy (or with layers of both) structure called a [[fruit]]. Gymnosperm seeds begin their development "naked" on the bracts of cones, although the seeds do become covered by the [[Conifer cone|cone]] scales as they develop. An example of a hard fruit layer surrounding the actual seed is that of the so-called ''[[Drupe|stone]]'' fruits (such as the [[peach]]).
| |
| − | | |
| − | Some seeds have an appendage on the seed coat such an [[aril]] (as in [[yew]] and [[nutmeg]]) or an [[elaiosome]] (as in [[Corydalis]]) or hairs (as in [[cotton]]). The hilum is the scar on the seed coat where the seed was attached to the ovary wall by the funiculus.
| |
| − | | |
| − | 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]]. For seeds with a very thick coat, scarification of the seed coat may be necessary before water can reach the embryo. Examples of scarification include: gnawing by animals, freezing and thawing, battering on rocks in a stream bed, or passing through an animal's digestive tract. In the latter case, the seed coat protects the seed from [[digestion]], while perhaps 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. 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. [[Abscisic acid]] is usually the growth inhibitor in seeds.
| |
| − | | |
| − | == Seed functions ==
| |
| − | 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.
| |
| − | [[image:Photos-photos_1088103921_Floating.jpg|thumbnail|200px|right|Dandelion seeds ([[achene]]s) can be carried long distances by the wind.]]
| |
| − | 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 population through 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. Seed dispersal is often attributed mainly to fruits, however many seeds aid in their own dispersal, for example:
| |
| − | * 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.
| |
| − | * 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 attrac
| |
| − | tive 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 stores more than it needs, forgets where it has stored the seed, or dies.
| |
| − | * 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 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.
| |
| − | * Some seeds have appendages called [[elaiosome]]s, e.g. [[bloodroot]], [[trillium]]s and [[Acacia]]s. Elaiosomes provide food for [[ant]]s, which usually disperse such seeds. <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>
| |
| − | * 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 [http://www.seabean.com/].
| |
| − | | |
| − | 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. [http://links.jstor.org/sici?sici=0002-9122(197809)65:8%3C891:PAPEOA%3E2.0.CO;2-S]</ref>
| |
| − | | |
| − | One important function of most seeds is delaying germination to allow time for dispersal and to prevent all seeds from germinating at once when conditions are favorable. Staggering germination prevents all seeds from germinating at once and being wiped out by bad weather or herbivores. [[Seed dormancy]] is defined as a seed failing to germinate under environmental conditions optimal for germination. It is often confused with seed quiescence, which is a seed failing to germinate because environmental conditions are inappropriate for germination. Many cultivated seeds lack dormancy but do not germinate in seed packets simply because there is insufficient moisture.
| |
| − | | |
| − | ==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.
| |
| − | | |
| − | 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:ElmBlossom.jpg|thumb|Immature [[Elm]] seeds.]]
| |
| − | Many seeds are [[List of edible seeds|edible]]. 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.
| |
| − | | |
| − | Seeds are used to propagate many crops such as cereals, legumes, [[forestry|forest trees]], [[turfgrass]]es and [[pasture]] grasses.
| |
| − | | |
| − | Some seeds are also poisonous. One of the deadliest poisons, [[ricin]], comes from seeds of the [[castor bean]]. Another seed poison is [[strychnine]]. Other poisonous seeds are those of [[yew]], [[wisteria]], [[apple]], [[horse-chestnut]] and [[peach]].
| |
| − | | |
| − | 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 (Melaleuca 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]].
| |
| − | * Many seeds used as [[birdseed]].
| |
| − | | |
| − | ==Oldest viable seeds==
| |
| − | {{main|oldest viable seed}} | |
| − | *The oldest [[carbon-14]]-dated seed that has grown into a viable 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. [http://news.nationalgeographic.com/news/2005/11/1122_051122_old_seed.html]
| |
| − | | |
| − | == Seed packets and seed information ==
| |
| − | [[Image:South Central Farm 1.jpg|thumb|A farmer's son holding out seeds]]
| |
| − | Generally, seed packets labels includes:
| |
| − | * Common plant name and the [[botanical]] name (in parentheses).
| |
| − | * Space and deep: how deep to place the seeds in the [[soil]], space between plants (from one [[row]] to the other one and from one plant to the other one in the same row).
| |
| − | * [[Height]]: approximate [[height]] the plant will reach when mature.
| |
| − | * [[Soil]]: type of soil the plant prefers.
| |
| − | * [[Water]]: It can indicate "keep the soil lightly [[damp]]", "bottom water the plant", "[[drench]] the soil with water", "daily [[misting]] of water" and "almost [[dry]] out before re-watering".
| |
| − | * [[Sun]]: full direct sunlight, partial sun, diffused sunlight, or grows well in the [[shade]].
| |
| − | * Door: if the plant is best suited for growing [[Indoor]], [[Outdoor]] or Both.
| |
| − | * Live: [[perennial plant|Perennial]] or [[annual plant|annual]].
| |
| − | * [[Planting]], [[germination]] and [[harvest]] [[period]]: This information can be indicated by months or [[quarter]]s of the year.
| |
| − | * Special requirements, if necessary.
| |
| − | This information can be represented graphically.
| |
| − | | |
| − | == See also ==
| |
| − | * [[Biological dispersal]]
| |
| − | * [[List of edible seeds]]
| |
| − | * [[Seed company]]
| |
| − | * [[Seed predation]]
| |
| − | * [[Seedbed]]
| |
| − | * [[Seedhead]]s
| |
| − | * [[Stratification (botany)|Stratification]]
| |
| − | | |
| − | == References ==
| |
| − | {{Commons|Seed}}
| |
| − | {{Portalpar|Biology}}
| |
| − | <references/>
| |
| − | | |
| − | ==External links==
| |
| − | * [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.
| |
| − | | |
| − | [[Category:Agronomy]]
| |
| − | [[Category:Botany]]
| |
| − | [[Category:Forestry]]
| |
| − | [[Category:Horticulture]]
| |
| − | [[Category:Plant morphology]]
| |
| − | [[Category:Plant reproduction]]
| |