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Seed

2007 Schools Wikipedia Selection. Related subjects: General Biology; Plants

   A ripe red jalapeno cut open to show the seeds
   Enlarge
   A ripe red jalapeno cut open to show the seeds

   A seed is the ripened ovule of gymnosperm or angiosperm plants. The
   importance of the seed relative to more primitive forms of reproduction
   and dispersal is attested to by the success of these two groups of
   plants in dominating the landscape.

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 food
   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. Orchid seeds have immature embryos and no
   significant food reserves. They are 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 monocotyledons, two
   cotyledons in almost all dicotyledons 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 oil or starch
   and protein. In gymnosperms, such as conifers, 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, sunflower, and radish. Seeds with an
   endosperm at maturity are termed albuminous seeds. Most monocots (e.g.
   grasses and 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 cone scales as they develop. An example of a hard
   fruit layer surrounding the actual seed is that of the so-called 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.
   Dandelion seeds (achenes) can be carried long distances by the wind.
   Enlarge
   Dandelion seeds ( achenes) 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 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 orchids 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) which is
       eaten by animals (birds, mammals) which then disperse the seeds in
       their droppings.
     * Seeds ( nuts) which are an attractive long-term storable food
       resource for animals (e.g. acorns, hazelnut, 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 ( burrs) with barbs or hooks (e.g. acaena, burdock, dock)
       which attach to animal fur or feathers, and then drop off later.
     * Seeds of some mangroves 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 elaiosomes, e.g. bloodroot,
       trilliums and Acacias. Elaiosomes provide food for ants, which
       usually disperse such seeds.
     * 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 .

   For 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.

   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 theatre of their true first evolutionary radiation. The
   seed plants progressively became one of the major elements of nearly
   all ecosystems.

Economic importance

   Immature Elm seeds.
   Enlarge
   Immature Elm seeds.

   Many seeds are edible. The majority of human calories comes from seeds,
   especially from cereals, legumes and nuts. Seeds also provide most
   cooking oils, many beverages and spices and some important food
   additives.

   Seeds are used to propagate many crops such as cereals, legumes, forest
   trees, turfgrasses 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 fibre 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, Laetrile.

   Many seeds have been used as beads in necklaces and rosaries including
   Job's tears, Chinaberry and rosary pea. However, the latter two are
   also poisonous.

   Other seed uses include:
     * Seeds once used as weights for balances.
     * 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

     * 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.

     * If the 2,000 year old Judean date palm seed longevity claim is
       confirmed by a report in a refereed scientific journal, then the
       second oldest viable seed would be the carbon-14-dated
       1,300-year-old sacred lotus ( Nelumbo nucifera), recovered from a
       dry lakebed in northeastern China.

     * There is a persistent myth that seeds from Egyptian tombs with ages
       of over 3,000 years were viable . The myth was reportedly started
       by scam artists selling "miracle seed" designed to capitalise on
       European Egyptomania of the 1800s. In 1897, the claims were tested
       by the British Museum's director of Egyptian antiquities, E. A.
       Wallis Budge. Budge provided genuine 3,000-year-old tomb-seeds to
       the Royal Botanic Gardens, Kew to plant under controlled
       conditions. The test resulted in no germination.

Seed packets and seed information

   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 or annual.
     * Planting, germination and harvest period: a lot of plant germinates
       in March. This information can be indicated by months or quarters
       of the year.
     * Special requirements, if necessary.

   This information can be represented graphically.

   Retrieved from " http://en.wikipedia.org/wiki/Seed"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
