A seed is an embryonic plant enclosed in a protective outer covering.
The formation of the seed is part of the process of reproduction in
seed plants, the spermatophytes, including the gymnosperm and
Seeds are the product of the ripened ovule, after fertilization by
pollen and some growth within the mother plant. The embryo is
developed from the zygote and the seed coat from the integuments of
Seeds have been an important development in the reproduction and
success of gymnosperm and angiosperm plants, relative to more
primitive plants such as ferns, mosses and liverworts, which do not
have seeds and use water-dependent means to propagate themselves. Seed
plants now dominate biological niches on land, from forests to
grasslands both in hot and cold climates.
The term "seed" also has a general meaning that antedates the
above—anything that can be sown, e.g. "seed" potatoes, "seeds" of
corn or sunflower "seeds". In the case of sunflower and corn "seeds",
what is sown is the seed enclosed in a shell or husk, whereas the
potato is a tuber.
Many structures commonly referred to as "seeds" are actually dry
fruits. Plants producing berries are called baccate.
are sometimes sold commercially while still enclosed within the hard
wall of the fruit, which must be split open to reach the seed.
Different groups of plants have other modifications, the so-called
stone fruits (such as the peach) have a hardened fruit layer (the
endocarp) fused to and surrounding the actual seed. Nuts are the
one-seeded, hard-shelled fruit of some plants with an indehiscent
seed, such as an acorn or hazelnut.
3 Shape and appearance
4.5 Size and seed set
5.2.1 By wind (anemochory)
5.2.2 By water (hydrochory)
5.2.3 By animals (zoochory)
5.4 Persistence and seed banks
6.1 Repair of DNA damage
6.2 Inducing germination
6.3 Sterile seeds
6.4 Evolution and origin of seeds
7 Economic importance
7.1 Edible seeds
7.2 Poison and food safety
7.3 Other uses
9 In religion
10 See also
13 External links
Seeds are produced in several related groups of plants, and their
manner of production distinguishes the angiosperms ("enclosed seeds")
from the gymnosperms ("naked seeds").
Angiosperm seeds are produced in
a hard or fleshy structure called a fruit that encloses the seeds for
protection in order to secure healthy growth. Some fruits have layers
of both hard and fleshy material. 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
cone scales as they develop in some species of conifer.
Seed production in natural plant populations varies widely from year
to year in response to weather variables, insects and diseases, and
internal cycles within the plants themselves. Over a 20-year period,
for example, forests composed of loblolly pine and shortleaf pine
produced from 0 to nearly 5 million sound pine seeds per hectare.
Over this period, there were six bumper, five poor, and nine good seed
crops, when evaluated for production of adequate seedlings for natural
Stages of seed development:
VI Mature Embryo
Embryo 4. Suspensor 5. Cotyledons 6.
Radicle 9. Hypocotyl
10. Epicotyl 11.
Angiosperm (flowering plants) 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, which
involves the fusion of two male gametes with the egg cell and the
central cell to form the primary endosperm and the zygote. Right after
fertilization, the zygote is mostly inactive, but the primary
endosperm divides rapidly to form the endosperm tissue. This tissue
becomes the food the young plant will consume until the roots have
developed after germination.
Main article: Ovule
Gymnosperm ovule on left, angiosperm ovule (inside
ovary) on right
After fertilization the ovules develop into the seeds. The ovule
consists of a number of components:
The funicle (funiculus, funiculi) or seed stalk which attaches the
ovule to the placenta and hence ovary or fruit wall, at the pericarp.
The nucellus, the remnant of the megasporangium and main region of the
ovule where the megagametophyte develops.
The micropyle, a small pore or opening in the apex of the integument
of the ovule where the pollen tube usually enters during the process
The chalaza, the base of the ovule opposite the micropyle, where
integument and nucellus are joined together.
The shape of the ovules as they develop often affects the final 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
megagametophyte 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 (the funicle or funiculus).
In the majority of flowering plants, the zygote's first division is
transversely oriented 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 manufactures nutrients from the
endosperm that are used during the embryo's growth.
The inside of a
Ginkgo seed, showing a well-developed embryo,
nutritive tissue (megagametophyte), and a bit of the surrounding seed
The main components of the embryo are:
The cotyledons, the seed leaves, attached to the embryonic axis. There
may be one (Monocotyledons), or two (Dicotyledons). The cotyledons are
also the source of nutrients in the non-endospermic dicotyledons, in
which case they replace the endosperm, and are thick and leathery. In
endospermic seeds the cotyledons are thin and papery. Dicotyledons
have the point of attachment opposite one another on the axis.
The epicotyl, the embryonic axis above the point of attachment of the
The plumule, the tip of the epicotyl, and has a feathery appearance
due to the presence of young leaf primordia at the apex, and will
become the shoot upon germination.
The hypocotyl, the embryonic axis below the point of attachment of the
cotyledon(s), connecting the epicotyl and the radicle, being the
stem-root transition zone.
The radicle, the basal tip of the hypocotyl, grows into the primary
Monocotyledonous plants have two additional structures in the form of
sheaths. The plumule is covered with a coleoptile that forms the first
leaf while the radicle is covered with a coleorhiza that connects to
the primary root and adventitious roots form from the sides. Here the
hypocotyl is a rudimentary axis between radicle and plumule. The seeds
of corn are constructed with these structures; pericarp, scutellum
(single large cotyledon) that absorbs nutrients from the 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 maturing ovule undergoes marked changes in the integuments,
generally a reduction and disorganisation but occasionally a
thickening. 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. (The seed coats of some mononocotyledon plants, such as the
grasses, are not distinct structures, but are fused with the fruit
wall to form a pericarp.) The testae of both monocots and dicots are
often marked with patterns and textured markings, or have wings or
tufts of hair. When the seed coat forms from only one layer, it is
also called the testa, though not all such testae are homologous from
one species to the next. The funiculus abscises (detaches at fixed
point – abscission zone), the scar forming an oval depression, the
hilum. Anatropous ovules have a portion of the funiculus that is
adnate (fused to the seed coat), and which forms a longitudinal ridge,
or raphe, just above the hilum. In bitegmic ovules (e.g. Gossypium
described here) both inner and outer integuments contribute to the
seed coat formation. With continuing maturation the cells enlarge in
the outer integument. While the inner epidermis may remain a single
layer, it may also divide to produce two to three layers and
accumulates starch, and is referred to as the colourless layer. By
contrast the outer epidermis becomes tanniferous. The inner integument
may consist of eight to fifteen layers. (Kozlowski 1972)
As the cells enlarge, and starch is deposited in the outer layers of
the pigmented zone below the outer epidermis, this zone begins to
lignify, while the cells of the outer epidermis enlarge radially and
their walls thicken, with nucleus and cytoplasm compressed into the
outer layer. these cells which are broader on their inner surface are
called palisade cells. In the inner epidermis the cells also enlarge
radially with plate like thickening of the walls. The mature inner
integument has a palisade layer, a pigmented zone with 15-20 layers,
while the innermost layer is known as the fringe layer. (Kozlowski
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In gymnosperms, which do not form ovaries, the ovules and hence the
seeds are exposed. This is the basis for their nomenclature – naked
seeded plants. Two sperm cells transferred from the pollen do not
develop the seed by double fertilization, but one sperm nucleus unites
with the egg nucleus and the other sperm is not used.
 Sometimes each sperm fertilizes an egg cell and one zygote is then
aborted or absorbed during early development. 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
such as pine and spruce.
Shape and appearance
A large number of terms are used to describe seed shapes, many of
which are largely self-explanatory such as Bean-shaped (reniform) –
resembling a kidney, with lobed ends on either side of the hilum,
Square or Oblong – angular with all sides more or less equal or
longer than wide, Triangular – three sided, broadest below middle,
Elliptic or Ovate or Obovate – rounded at both ends, or egg shaped
(ovate or obovate, broader at one end), being rounded but either
symmetrical about the middle or broader below the middle or broader
above the middle.
Other less obvious terms include discoid (resembling a disc or plate,
having both thickness and parallel faces and with a rounded margin),
ellipsoid, globose (spherical), or subglobose (Inflated, but less than
spherical), lenticular, oblong, ovoid, reniform and sectoroid. Striate
seeds are striped with parallel, longitudinal lines or ridges. The
commonest colours are brown and black, other colours are infrequent.
The surface varies from highly polished to considerably roughened. The
surface may have a variety of appendages (see
Seed coat). A seed coat
with the consistency of cork is referred to as suberose. Other terms
include crustaceous (hard, thin or brittle).
The parts of an avocado seed (a dicot), showing the seed coat and
Diagram of the internal structure of a dicot seed and embryo: (a) seed
coat, (b) endosperm, (c) cotyledon, (d) hypocotyl
A typical seed includes two basic parts:
a seed coat.
In addition, the endosperm forms a supply of nutrients for the embryo
in most monocotyledons and the endospermic dicotyledons.
Seeds have been considered to occur in many structurally different
types (Martin 1946). These are based on a number of criteria, of
which the dominant one is the embryo-to-seed size ratio. This reflects
the degree to which the developing cotyledons absorb the nutrients of
the endosperm, and thus obliterate it.
Six types occur amongst the monocotyledons, ten in the dicotyledons,
and two in the gymnosperms (linear and spatulate). This
classification is based on three characteristics: embryo morphology,
amount of endosperm and the position of the embryo relative to the
Diagram of a generalized dicot seed (1) versus a generalized monocot
seed (2). A.
Seed Coat B.
Cotyledon C. Hilum D. Plumule E.
In endospermic seeds, there are two distinct regions inside the seed
coat, an upper and larger endosperm and a lower smaller embryo. The
embryo is the fertilised ovule, an immature plant from which a new
plant will grow under proper conditions. The embryo has one cotyledon
or seed leaf in monocotyledons, two cotyledons in almost all
dicotyledons and two or more in gymnosperms. In the fruit of grains
(caryopses) the single monocotyledon is shield shaped and hence called
a scutellum. The scutellum is pressed closely against the endosperm
from which it absorbs food, and passes it to the growing parts. Embryo
descriptors include small, straight, bent, curved and curled.
Within the seed, there usually is a store of nutrients 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 mother plant and the pollen via double fertilization. It is
usually triploid, and is rich in oil or starch, and protein. In
gymnosperms, such as conifers, the food storage tissue (also called
endosperm) is part of the female gametophyte, a haploid tissue. The
endosperm is surrounded by the aleurone layer (peripheral endosperm),
filled with proteinaceous aleurone grains.
Originally, by analogy with the animal ovum, the outer nucellus layer
(perisperm) was referred to as albumen, and the inner endosperm layer
as vitellus. Although misleading, the term began to be applied to all
the nutrient matter. This terminology persists in referring to
endospermic seeds as "albuminous". The nature of this material is used
in both describing and classifying seeds, in addition to the embryo to
endosperm size ratio. The endosperm may be considered to be
farinaceous (or mealy) in which the cells are filled with starch, as
for instance cereal grains, or not (non-farinaceous). The endosperm
may also be referred to as "fleshy" or "cartilaginous" with thicker
soft cells such as coconut, but may also be oily as in
oil), Croton and Poppy. The endosperm is called "horny" when the cell
walls are thicker such as date and coffee, or "ruminated" if mottled,
as in nutmeg, palms and Annonaceae.
In most monocotyledons (such as grasses and palms) and some
(endospermic or albuminous) dicotyledons (such as castor beans) the
embryo is embedded in the endosperm (and nucellus), which the seedling
will use upon germination. In the non-endospermic dicotyledons the
endosperm is absorbed by the embryo as the latter grows within the
developing seed, and the cotyledons of the embryo become filled with
stored food. At maturity, seeds of these species have no endosperm and
are also referred to as exalbuminous seeds. The exalbuminous seeds
include the legumes (such as beans and peas), trees such as the oak
and walnut, vegetables such as squash and radish, and sunflowers.
According to Bewley and Black (1978), Brazil nut storage is in
hypocotyl, this place of storage is uncommon among seeds. All
gymnosperm seeds are albuminous.
The seed coat develops from the maternal tissue, the integuments,
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), or fleshy as in the
sarcotesta of pomegranate. The seed coat helps protect the embryo from
mechanical injury, predators and drying out. Depending on its
development, the seed coat is either bitegmic or unitegmic. Bitegmic
seeds form a testa from the outer integument and a tegmen from the
inner integument while unitegmic seeds have only one integument.
Usually parts of the testa or tegmen form a hard protective mechanical
layer. The mechanical layer may prevent water penetration and
germination. Amongst the barriers may be the presence of lignified
The outer integument has a number of layers, generally between four
and eight organised into three layers: (a) outer epidermis, (b) outer
pigmented zone of two to five layers containing tannin and starch, and
(c) inner epidermis. The endotegmen is derived from the inner
epidermis of the inner integument, the exotegmen from the outer
surface of the inner integument. The endotesta is derived from the
inner epidermis of the outer integument, and the outer layer of the
testa from the outer surface of the outer integument is referred to as
the exotesta. If the exotesta is also the mechanical layer, this is
called an exotestal seed, but if the mechanical layer is the
endotegmen, then the seed is endotestal. The exotesta may consist of
one or more rows of cells that are elongated and pallisade like (e.g.
Fabaceae), hence 'palisade exotesta'.
In addition to the three basic seed parts, some seeds have an
appendage, an aril, a fleshy outgrowth of the funicle (funiculus), (as
in yew and nutmeg) or an oily appendage, an elaiosome (as in
Corydalis), or hairs (trichomes). In the latter example these hairs
are the source of the textile crop cotton. Other seed appendages
include the raphe (a ridge), wings, caruncles (a soft spongy outgrowth
from the outer integument in the vicinity of the micropyle), spines,
A scar also may remain on the seed coat, called the hilum, where the
seed was attached to the ovary wall by the funicle. Just below it is a
small pore, representing the micropyle of the ovule.
Size and seed set
A collection of various vegetable and herb seeds
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
Orchids and a few other groups of plants are
mycoheterotrophs 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 lives deriving energy from the fungi and do not produce green
leaves. 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 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
Seeds serve several functions for the plants that produce them. Key
among these functions are nourishment of the embryo, dispersal to a
new location, and dormancy during unfavorable conditions. Seeds
fundamentally are means of reproduction, and most seeds are the
product of sexual reproduction which produces a remixing of genetic
material and phenotype variability on which natural selection acts.
Seeds protect and nourish the embryo or young plant. They usually give
a seedling a faster start than a sporeling from a spore, because of
the larger food reserves in the seed and the multicellularity of the
Unlike animals, plants are limited in their ability to seek out
favorable conditions for life and growth. As a result, plants have
evolved many ways to 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 the fruits
achenes, caryopsis, nuts, samaras, and utricles.
By wind (anemochory)
Dandelion seeds are contained within achenes, which can be carried
long distances by the wind.
The seed pod of milkweed (Asclepias syriaca)
Some seeds (e.g., pine) have a wing that aids in wind dispersal.
The dustlike seeds of orchids are carried efficiently by the wind.
Some seeds (e.g. milkweed, poplar) have hairs that aid in wind
Other seeds are enclosed in fruit structures that aid wind dispersal
in similar ways:
Dandelion achenes have hairs.
Maple samaras have two wings.
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.
By animals (zoochory)
Seeds (burrs) with barbs or hooks (e.g. acaena, burdock, 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 (birds, mammals, reptiles, fish) which then disperse these
seeds in their droppings.
Seeds (nuts) are attractive long-term storable food resources 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 forgets them.
Myrmecochory is the dispersal of seeds by ants. Foraging ants disperse
seeds which have appendages called elaiosomes (e.g. bloodroot,
trilliums, acacias, 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. 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 invaded and displaced native species of ants.
Unlike the native ant species, Argentine ants do not collect the seeds
Mimetes cucullatus or eat the elaiosomes. In areas where these ants
have invaded, the numbers of Mimetes seedlings have dropped.
Seed dormancy has two main functions: the first is synchronizing
germination with the optimal conditions for survival of the resulting
seedling; the second is spreading germination of a batch of seeds over
time so a catastrophe (e.g. late frosts, drought, herbivory) does not
result in the death of all offspring of a plant (bet-hedging).
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.
This true dormancy or innate dormancy is therefore caused by
conditions within the seed that prevent germination. Thus dormancy is
a state of the seed, not of the environment. Induced dormancy,
enforced dormancy or seed quiescence occurs when a seed fails to
germinate because the external environmental conditions are
inappropriate for germination, mostly in response to conditions being
too dark or light, too cold or hot, or too dry.
Seed dormancy is not the same as seed persistence in the soil or on
the plant, though even in scientific publications dormancy and
persistence are often confused or used as synonyms.
Often, seed dormancy is divided into four major categories: exogenous;
endogenous; combinational; and secondary. A more recent system
distinguishes five classes: morphological, physiological,
morphophysiological, physical, and combinational dormancy.
Exogenous dormancy is caused by conditions outside the embryo,
Physical dormancy or hard seed coats occurs when seeds are impermeable
to water. At dormancy break, a specialized structure, the ‘water
gap’, is disrupted in response to environmental cues, especially
temperature, so water can enter the seed and germination can occur.
Plant families where physical dormancy occurs include Anacardiaceae,
Fabaceae and Malvaceae.
Chemical dormancy considers species that lack physiological dormancy,
but where a chemical prevents germination. This chemical can be
leached out of the seed by rainwater or snow melt or be deactivated
somehow. Leaching of chemical inhibitors from the seed by rain
water is often cited as an important cause of dormancy release in
seeds of desert plants, but little evidence exists to support this
Endogenous dormancy is caused by conditions within the embryo itself,
In morphological dormancy, germination is prevented due to
morphological characteristics of the embryo. In some species, the
embryo is just a mass of cells when seeds are dispersed; it is not
differentiated. Before germination can take place, both
differentiation and growth of the embryo have to occur. In other
species, the embryo is differentiated but not fully grown
(underdeveloped) at dispersal, and embryo growth up to a species
specific length is required before germination can occur. Examples of
plant families where morphological dormancy occurs are Apiaceae,
Magnoliaceae and Ranunculaceae.
Morphophysiological dormancy includes seeds with underdeveloped
embryos, and also 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.
Plant families where
morphophysiological dormancy occurs include Apiaceae, Aquifoliaceae,
Papaveraceae and Ranunculaceae. Some
plants with morphophysiological dormancy, such as
Asarum or Trillium
species, have multiple types of dormancy, one affects radicle (root)
growth, while the other affects plumule (shoot) growth. The terms
"double dormancy" and "two-year seeds" are used for species whose
seeds need two years to complete germination or at least two winters
and one summer.
Dormancy of the radicle (seedling root) is broken
during the first winter after dispersal while dormancy of the shoot
bud is broken during the second winter.
Physiological dormancy means the embryo, due to physiological causes,
cannot generate enough power to break through the seed coat, endosperm
or other covering structures.
Dormancy is typically broken at cool
wet, warm wet or warm dry conditions.
Abscisic acid is usually the
growth inhibitor in seeds, and its production can be affected by
Drying, in some plants, including a number of grasses and those from
seasonally arid regions, is needed before they will germinate. The
seeds are released, but need to have a lower moisture 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
In seeds with combinational dormancy, the seed or fruit coat is
impermeable to water and the embryo has physiological dormancy.
Depending on the species, physical dormancy can be broken before or
after physiological dormancy is broken.
Secondary dormancy* is caused by conditions after the seed has been
dispersed and occurs in some seeds when nondormant 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.
The following types of seed dormancy do not involve seed dormancy,
strictly speaking, as lack of germination is prevented by the
environment, not by characteristics of the seed itself (see
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
Thermodormancy is seed sensitivity to heat or cold. Some seeds,
including cocklebur and amaranth, germinate only at high temperatures
(30 °C or 86 °F); many plants that have seeds that
germinate in early to midsummer have thermodormancy, so germinate only
when the soil temperature is warm. Other seeds need cool soils to
germinate, while others, such as celery, are inhibited when soil
temperatures are too warm. Often, thermodormancy requirements
disappear as the seed ages or dries.
Not all seeds undergo a period of dormancy. 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. Many garden plant seeds 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 it.
After many generations of selective pressure by plant breeders and
gardeners, dormancy has been selected out.
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.
Persistence and seed banks
Seedling and Germination
Germinating sunflower seedlings
Seed germination is a process by which a seed embryo develops into a
seedling. 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. The emergence of the seedling above the soil surface
is the next phase of the plant's growth and is called seedling
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 overcome. (3) The proper
environmental conditions must exist for germination.
Seed viability is the ability of the embryo to germinate 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.
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
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. 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 affecting 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 drying then becomes fatal. Other seeds
can imbibe and lose water a few times without causing ill effects, but
drying can cause secondary dormancy.
Repair of DNA damage
During seed dormancy, often associated with unpredictable and
stressful environments, DNA damage accumulates as the seeds
age. In rye seeds, the reduction of DNA integrity due to
damage is associated with loss of seed viability during storage.
Upon germination, seeds of
Vicia faba undergo DNA repair. A plant
DNA ligase that is involved in repair of single- and double-strand
breaks during seed germination is an important determinant of seed
longevity. Also, in
Arabidopsis seeds, the activities of the DNA
repair enzymes Poly ADP ribose polymerases (PARP) are likely needed
for successful germination. Thus DNA damages that accumulate
during dormancy appear to be a problem for seed survival, and the
enzymatic repair of DNA damages during germination appears to be
important for seed viability.
A number of different strategies are used by gardeners and
horticulturists to break seed dormancy.
Scarification allows water and gases to penetrate into the seed; it
includes methods to physically break the hard seed coats or soften
them by chemicals, such as 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. 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 is deposited, along
with a bit of fecal matter that acts as fertilizer, far from the
parent plant. Microorganisms 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
Stratification, also called moist-chilling, breaks down physiological
dormancy, and involves the addition of moisture to the seeds so they
absorb water, and they are then subjected to a period of moist
chilling to after-ripen the embryo.
Sowing in late summer and fall and
allowing to overwinter under cool conditions is an effective way to
stratify seeds; some seeds respond more favorably to periods of
oscillating temperatures which are a 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, 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, such as gibberellins, cytokinins, ethylene,
thiourea, sodium hypochlorite, and others. Some seeds germinate
best after a fire. For some seeds, fire cracks hard seed coats, while
in others, 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.
Seeds may be sterile for few reasons: they may have been irradiated,
unpollinated, cells lived past expectancy, or bred for the purpose.
Evolution and origin of seeds
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
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. With
this radiation came an evolution of seed size, shape, dispersal and
eventually the radiation of gymnosperms and angiosperms and
monocotyledons and dicotyledons. The seed plants progressively became
one of the major elements of nearly all ecosystems.
Phaseolus vulgaris (common bean or green bean) seeds are diverse in
size, shape, and color.
Further information: List of edible seeds
Many seeds are edible and 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. In different seeds the seed embryo or the
endosperm dominates and provides most of the nutrients. The storage
proteins of the embryo and endosperm differ in their amino acid
content and physical properties. For example, the gluten of wheat,
important in providing the elastic property to bread dough is strictly
an endosperm protein.
Seeds are used to propagate many crops such as cereals, legumes,
forest trees, turfgrasses, and pasture grasses. Particularly in
developing countries, a major constraint faced is the inadequacy of
the marketing channels to get the seed to poor farmers. Thus the
use of farmer-retained seed remains quite common.
Seeds are also eaten by animals, and are fed to livestock. Many seeds
are used as birdseed.
Poison and food safety
While some seeds are edible, others are harmful, poisonous or
deadly. Plants and seeds often contain chemical compounds to
discourage herbivores and seed predators. In some cases, these
compounds simply taste bad (such as in mustard), but other compounds
are toxic or break down into toxic compounds within the digestive
system. Children, being smaller than adults, are more susceptible to
poisoning by plants and seeds.
A deadly poison, ricin, comes from seeds of the castor bean. Reported
lethal doses are anywhere from two to eight seeds, though only
a few deaths have been reported when castor beans have been ingested
In addition, seeds containing amygdalin—apple, apricot, bitter
almond, peach, plum, cherry, quince, and others—when consumed in
sufficient amounts, may cause cyanide poisoning. Other seeds
that contain poisons include annona, cotton, custard apple, datura,
uncooked durian, golden chain, horse-chestnut, larkspur, locoweed,
lychee, nectarine, rambutan, rosary pea, sour sop, sugar apple,
wisteria, and yew. The seeds of the strychnine tree are also
poisonous, containing the poison 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
Please see the category plant toxins for further relevant articles.
Cotton fiber grows attached to cotton plant seeds. 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 quack cancer drug Laetrile.
Many seeds have been used as beads in necklaces and rosaries including
Job's tears, Chinaberry, rosary pea, and castor bean. However, the
latter three 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 Conkers.
Clusia rosea seeds used to caulk boats.
Nematicide from milkweed seeds.
Cottonseed meal used as animal feed and fertilizer.
The massive fruit of the coco de mer
The oldest viable carbon-14-dated seed that has grown into a plant was
Judean date palm
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. (A reported regeneration of Silene stenophylla
(narrow-leafed campion) from material preserved for 31,800 years in
the Siberian permafrost was achieved using fruit tissue, not
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.
The smallest seeds are produced by epiphytic orchids. They are only 85
micrometers long, and weigh 0.81 micrograms. They have no endosperm
and contain underdeveloped embryos.
The earliest fossil seeds are around 365 million years old from the
Devonian of West Virginia. The seeds are preserved immature
ovules of the plant Elkinsia polymorpha.
Book of Genesis
Book of Genesis in the Old Testament begins with an explanation of
how all plant forms began:
God said, Let the earth bring forth grass, the herb yielding seed,
and the fruit tree yielding fruit after his kind, whose seed is in
itself, upon the earth: and it was so. And the earth brought forth
grass, and herb yielding seed after its kind, and the tree yielding
fruit, whose seed was in itself, after its kind: and
God saw that it
was good. And the evening and the morning were the third day.
Quran speaks about seed germination:
Allah Who causeth the seed-grain and the date-stone to split and
sprout. He causeth the living to issue from the dead, and He is the
one to cause the dead to issue from the living. That is Allah: then
how are ye deluded away from the truth?
Genetically modified crops
List of world's largest seeds
Soil seed bank
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Wikimedia Commons has media related to Seed.
Look up seed in Wiktionary, the free dictionary.
Royal Holloway, University of London: The
Seed Biology Place
Seed Bank Project Kew Garden's ambitious preservation
The Svalbard Global
Seed Vault – a backup facility for the world's
Plant Physiology online: Types of
Dormancy and the Roles of
Canadian Grain Commission:
Seed characters used in the identification
of small oilseeds and weed seeds
Seed Site: collecting, storing, sowing, germinating, and
exchanging seeds, with pictures of seeds, seedpods and seedlings.
Plant Fix: Check out various plant seeds and learn more information
History of botany
Hypanthium (Floral cup)
Plant growth and habit
Alternation of generations
History of plant systematics
International Code of Nomenclature for algae, fungi, and plants
International Code of Nomenclature for algae, fungi, and plants (ICN)
- for Cultivated Plants (ICNCP)
International Association for
Plant Taxonomy (IAPT)
Plant taxonomy systems
Cultivated plant taxonomy
by author abbreviation
BNF: cb12573148r (d