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See study by J. Silvertown (2009).
A fertilized ovule containing an embryo which forms a new plant upon germination. Seed-bearing characterizes the higher plants—the gymnosperms (conifers and allies) and the angiosperms (flowering plants). Gymnosperm (naked) seeds arise on the surface of a structure, as on a seed scale of a pine cone. Angiosperm (covered) seeds develop within a fruit, as the peas in a pod. See Flower, Fruit
One or two tissue envelopes, or integuments, form the seed coat which encloses the seed except for a tiny pore, the micropyle (see illustration). The micropyle is near the funiculus (seed stalk) in angiosperm seeds. The hilum is the scar left when the seed is detached from the funiculus. Some seeds have a raphe, a ridge near the hilum opposite the micropyle, and a bulbous strophiole. Others such as nutmeg possess arils, outgrowths of the funiculus, or a fleshy caruncle developed from the seed coat near the hilum, as in the castor bean. The embryo consists of an axis and attached cotyledons (seed leaves). The part of the axis above the cotyledons is the epicotyl (plumule); that below, the hypocotyl, the lower end of which bears a more or less developed primordium of the root (radicle). The epicotyl, essentially a terminal bud, possesses an apical meristem (growing point) and, sometimes, leaf primordia. The seedling stem develops from the epicotyl. An apical meristem of the radicle produces the primary root of the seedling, and transition between root and stem occurs in the hypocotyl. See Apical meristem, Root (botany), Stem
Two to many cotyledons occur in different gymnosperms. The angiosperms are divided into two major groups according to number of cotyledons: the monocotyledons and the dicotyledons. Mature gymnosperm seeds contain an endosperm (albumen or nutritive tissue) which surrounds the embryo. In some mature dicotyledon seeds the endosperm persists, the cotyledons are flat and leaflike, and the epicotyl is simply an apical meristem. In other seeds, such as the bean, the growing embryo absorbs the endosperm, and food reserve for germination is stored in fleshy cotyledons. The endosperm persists in common monocotyledons, for example, corn and wheat; and the cotyledon, known as the scutellum, functions as an absorbing organ during germination. Grain embryos also possess a coleoptile and a coleorhiza sheathing the epicotyl and the radicle, respectively. The apical meristems of lateral seed roots also may be differentiated in the embryonic axis near the scutellum of some grains.
Many so-called seeds consist of hardened parts of the fruit enclosing the true seed which has a thin, papery seed coat. Among these are the achenes, as in the sunflower, dandelion, and strawberry, and the pits of stone fruits such as the cherry, peach, and raspberry. Many common nuts also have this structure. Mechanisms for seed dispersal include parts of both fruit and seed. See Population dispersal
Propagation of plants by seed and technological use of seed and seed products are among the most important activities of modern society. Specializations of seed structure and composition provide rich sources for industrial exploitation apart from direct use as food. Common products include starches and glutens from grains, hemicelluloses from guar and locust beans, and proteins and oils from soybeans and cotton seed. Drugs, enzymes, vitamins, spices, and condiments are obtained from embryos, endosperms, and entire seeds, often including the fruit coat. Most of the oils of palm, olive, and pine seeds are in the endosperm. Safflower seed oil is obtained mainly from the embryo, whereas both the seed coat and embryo of cotton seed are rich in oils. See Food, Plant anatomy, Reproduction (plant)
Physical and biochemical processes of seed growth and germination are controlled by genetic and environmental factors. Conditions of light, temperature, moisture, and oxygen affect the timing and ability of a seed to mature and germinate. Seed development (embryogenesis) is concerned with the synthesis and storage of carbohydrate, protein, and oil to supply nutrients to the germinating seedling prior to soil emergence. Seed development occurs in several stages: rapid cell division, seed fill, and desiccation. The timing of each stage is species-specific and environmentally influenced.
Seed dormancy is the inability of a living seed to germinate under favorable conditions of temperature, moisture, and oxygen. Dormancy does not occur in all seeds, but typically occurs in plant species from temperate and colder habitats. This process allows for a delay in seed germination until environmental conditions are adequate for seedling survival. At least three types of seed dormancy are recognized: primary, secondary (induced), and enforced. Primary dormancy occurs during seed maturation, and the seed does not germinate readily upon being shed. Secondary and enforced dormancy occur after the seed is shed and may be caused by adverse environmental factors such as high or low temperature, absence of oxygen or light, low soil moisture, and presence of chemical inhibitors. Seeds with secondary dormancy will not germinate spontaneously when environmental conditions improve, and need additional environmental stimuli. Seeds with enforced dormancy germinate readily upon removal of the environmental limitation. Regulation of dormancy may be partly controlled by hormones. See Dormancy
Dormancy is terminated in a large number of species when an imbibed seed is illuminated with white light. Biochemical control of this process is related to the functioning of a single pigment, phytochrome, frequently located in the seed coat or embryonic axis. Phytochrome imparts to the seed the ability to interpret light quality, such as that under an existing vegetative canopy, and to distinguish light from dark with respect to its position in the soil. Phytochrome also is affected by temperature and is involved in the seasonal control of the ending of dormancy. Hormones that promote germination of dormant seeds include gibberellins, cytokinins, ethylene, and auxins.
Germination is the process whereby a viable seed takes up water and the radicle (primary root) or hypocotyl emerges from the seed under species-specific conditions of moisture, oxygen, and temperature. Dormant seeds must undergo additional environmental stimuli to germinate. The germinating seed undergoes cell expansion, as well as increases in respiration, protein synthesis, and other metabolic activities prior to emergence of the growing seedling.
an organ of seed plants that performs the functions of reproduction, repopulation, and, in unfavorable conditions, survival. In the course of evolution of heterosporous higher plants the seed arose in connection with changes in conditions of existence (for example, climatic conditions) as an ontogenetic phase between the sexual process that occurs within the megasporangium (the seed primordium and the ovule) and the adult plant. For this reason the seed usually develops after fertilization. It sometimes develops secondarily, without fertilization; this phenomenon is called apomixis. The number of seeds formed on a single plant cannot exceed the number of mega-sporangia that developed as a result of asexual reproduction.
In the first seed plants—seed ferns (Lyginopteridopsida)—the seeds probably developed on the ends or in the axils of the telomes. In gymnosperms the seeds develop on open sporophylls (seed scales); in angiosperms they develop in the fruit, which is formed mainly by closed carpels. The type of seed is determined by the type and orientation of the ovule from which the seed develops. In some cases, however, owing to uneven growth of the young seed after fertilization, the seed may differ in type from the ovule.
On the seed surface it is usually possible to distinguish the hilum, that is, the site where the mature seed abscises from the funiculus. The micropyle at the lower end may remain in the form of a pore; the remains of the chalaza on the end of the cotyledon are in the form of a variously colored spot, nodule, or pore. The raphe between the hilum and the chalaza in anatropous seeds arises as a result of concrescence of the upper part of the funiculus with the ovule. Often the seed has outgrowths, for example, an aril, a caruncle, arillods, or strophioles, which ensure myrmecochory. The surface of the seed may be smooth and glossy (pea), reticulately dimpled (henbane), thorny (cockle), nodular (chickweed), or scaly (monkshood). Some seeds form wings (eremurus, bignoniad) or hairs over the entire surface (cotton).
A seed consists of the testa (spermoderm), the embryo (young sporophyte), and, in many plants, the perisperm or endosperm (tissues with reserve nutrient matter that develop outside the embryo). The testa is formed from the integuments, or coverings, of the ovule and serves to protect the embryo and often to help in seed dispersal. When two integuments develop in the testa one may often distinguish an outer one (pomegranate and gooseberry have a succulent outer integument) and an inner one. When there is a single integument, sometimes owing to the destruction of the second one during seed development, the testa usually consists of several layers of cells. The hardness of the testa is increased as a result of tissue sclerification. A thin testa is characteristic of seeds of parasitic plants (for example, Orobanchaceae) and orchids, as well as of seeds enclosed in monospermous indehiscent fruits (for example, nuts). Seeds lacking a testa are found among Santalaceae, Loranthaceae, and other hemiparasites.
The embryo usually forms from the zygote, that is, the fertilized egg cell, and sometimes from other cells of the embryo sac or of the nucellus of the ovule (polyembriony). Embryos may vary in shape and in their position in relation to the testa, the perisperm, and the endosperm. Development of the embryo in the seed occurs owing to the accumulation of nutrient matter in the endosperm and perisperm or in the cotyledons. The endosperm in gymnosperms consists of a vegetative part of the, female prothallium; in angiosperms it consists of a neoplasm that arises as a result of the merging of the second spermatozoid with the secondary nucleus of the embryo sac (double fertilization). The perisperm consists of remains of tissue of the nucellus or of the nucleus of the ovule. A seed may contain both endosperm and perisperm (Piperaceae, Nymphaeaceae), endosperm only (Ranunculaceae), perisperm only (Caryophyllaceae), or neither (Leguminosae). In the last case the perisperm does not develop, the endosperm is completely absorbed by the developing embryo, and the nutrient matter is stored in the cells of the cotyledons. A seed with an endosperm is often incorrectly called albuminous. The presence of an endosperm and a perisperm in a seed is considered a primitive character.
The deposit of nutrient matter in the body of the embryo is progressive. Reserve substances of the seed include proteins, fats, starch, sugar, vitamins, and hemicelluloses. Formed inclusions are protein granules, often with crystals of protein, globoids of a double salt of inosinic acid, and crystals of calcium oxalate.
The external and internal structure of seeds is genetically constant and, thus, is useful in the taxonomy of plants. Seeds vary in size and weight; they range from tiny, dustlike particles in Orchidaceae (for example, a seed of Goodyera repens weighs 0.002 mg, and that of Dendrobium attenuatum 0.005 mg) to large nuts in palms (for example, the seed of a sea coconut weighs up to 9 kg). The number of seeds in a single fruit ranges from one (Gramineae, Compositae) to hundreds of thousands and even millions (in some Orchidaceae). The number of seeds in a single plant may be vast (in Amaranthus up to 500,000 and in Sisymbrium up to 750,000).
The length of time that a seed retains its viability varies in different species and depends on storage conditions. Thus, willow seeds generally remain viable for no longer than several days; in closed vessels at temperatures of 12°-13 °C, however, they retain their viability 150 to 320 days. The hard seeds of certain legumes can sprout after 100 years, and lotus seeds preserved in a layer of peat for several hundred years have proved to be viable.
Seeds are planted by man for use as food or food seasoning and to obtain oils, starch, dyes, medicines, and other substances. The seeds of many plants, as well as meal and oil cake made from them, are used as feed for cattle and poultry. The hairs of cotton seeds are used by the textile industry and in medicine (hygroscopic cotton).
Sometimes dry, indehiscent monospermous fruits (grains, buckwheat, flax), entire collective fruits (sugarbeet), and tubers (potato) are erroneously called seeds. The study of seeds is called seed science.
REFERENCESMal’tsev, A. I. Rukovodstvo po izucheniiu i opredeleniiu semian i plodov sornykh rastenii, part I. Leningrad, 1925. (Trudy po prikladnoi botanike i setektsii, supplement 25.)
Takhtadzhian, A. L. Morfologicheskaia evoliutsiia pokrylosemennykh. Moscow, 1948.
Tsinger, N. V. Semia, ego razvitie i fiziologicheskie svoistva. Moscow, 1958.
Eames, A. Morfologiia tsvetkovykh rastenii, Moscow, 1964. (Translated from English.)
Aleksandrov, V. G. Anatomiia rastenii, 4th ed. Moscow, 1966.
Botanika vol. 1.7th ed. Moscow, 1966.
Esau, K. Anatomiia rastenii. Moscow, 1969. (Translated from English.)
Gaetner, J. De fructibus et seminibus plantarum. Stuttgart, 1788.
Martin, A. C. “The Comparative Internal Morphology of Seeds.” The American Midland Naturalist, 1946, vol. 36, no. 3, pp. 513–660.
N. N. KADEN
What does it mean when you dream about a seed?
The seed represents reproduction of life—human, animal, or plant. Everything from the knowledge we import (“plant a seed in their memory”) to the money we use to finance business ventures (seed money) germinates metaphorically from a “seed.” A seed may indicate an idea has been planted in the dreamer’s mind and is germinating into new life experiences.
seed(1) The starting value used by a random number generation routine to create random numbers.
(2) A BitTorrent user who has a file that can be downloaded to another user. See BitTorrent seed.
(3) (seed accelerator) See startup accelerator.
(4) A series of words from which a private cryptocurrency key is created. See seed phrase.
(5) (SEED) (Self-Electro-optic-Effect Device) An optical transistor developed by David Miller at Bell Labs in 1986.