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A disease of the nervous system characterized by a progressive dementia that leads to profound impairment in cognition and behavior. Dementia occurs in a number of brain diseases where the impairment in cognitive abilities represents a decline from…

A neurodevelopmental condition that impairs the way that a person relates to and communicates with other people. Persons with autism have difficulties with social communication and interaction. They also can have unusual behaviors, such as…

A kind of mathematics whose variables can only be True or False. A variable is called Boolean if it can only hold two possible values: True or False. The value True can be represented by the number one and False by zero. For example, if A is a…

The internal structures and processes that are involved in the acquisition and use of knowledge, including sensation, perception, attention, learning, memory, language, thinking, and reasoning. The mental processes and behaviors that constitute…

A psychotherapy with roots in both cognitive science and behavioral science. Cognitive-behavioral therapy (CBT) is the most widely used evidence-based psychotherapeutic practice for a variety of mental health disorders, including anxiety, depression…

A syndrome characterized by a generalized decline in cognition that is severe enough to cause functional impairment in daily activities. Dementia is a term used to describe a collection of symptoms of severe cognitive decline. Individuals suffering…

A term commonly associated with both behaviors and states of mind (known as feelings) that are not under the control of reason and disturb the flow of consciously directed behavior. Emotions influence human thinking and behavior (Fig. 1), and they…

A mathematical system that details the properties and relationships of spatial objects such as points, lines, shapes, and planes. Euclidean geometry is also known as flat geometry or planar geometry, because planes in Euclidean geometry have the…

The use of pollen and spore evidence in legal cases. In its broader application, the field of forensic palynology also includes legal information derived from the analysis of a broad range of microscopic organisms that can be found in both fresh and…

A plant that has altered genetic material (DNA) through recombinant DNA (rDNA) manipulation. Genetic engineering of plants allows for very specific genetic changes to be made to a plant's deoxyribonucleic acid (DNA), as opposed to the random…

A commercially grown plant that has altered genetic material through artificial recombinant manipulation. Genetic modification is the latest scientific tool for developing improved crop varieties. Such genetically modified (GM) crops can help to…

The inverse function of an exponential function in mathematics. Stated less technically, a logarithm is the opposite of an exponent. Logarithms are used to solve equations in which the variable is an exponent. Historically, tables of logarithms…

The mental ability to store and access information that has been acquired through experience. Memory (Fig. 1) is a critical component of practically all aspects of human thinking, including perception, learning, language, and problem solving.…

A branch of mathematics involving numerical measures of how likely it is that a particular event will occur. A probability is a number between 0 and 1. An event that will never occur has a probability of zero, and an event that is certain to occur…

In medicine and health sciences, a value expected for an individual whose state of health is known and well described, and the interval of values broadly expected for a population, respectively. Results of clinical laboratory tests and other…

The field of knowledge concerned with collecting, analyzing, and presenting data. Statistical methods are regularly used by researchers in the physical, biological, and social sciences, as well as engineers, business managers, government officials…

A plant, Musa textilis, of the banana family that is valuable for its hard fiber (also known as Manila hemp). Abaca (Musa textilis) is a flowering plant native to the Philippines and Borneo. Taxonomically, it is assigned to the order Zingiberales.…

A major plant hormone that plays an important role in plant growth and development. Abscisic acid (ABA), with a chemical formula of C15H20O4 (Fig. 1), is one of the most significant hormones found in plants. It is responsible for regulating various…

The study of systems consisting of arbitrary sets of elements of unspecified type, together with certain operations satisfying prescribed lists of axioms. Abstract algebra has been developed since the mid-1920s and has become a basic idiom of…

Habituation to a specific practice, such as drinking alcoholic beverages or using drugs (for example, heroin, cocaine, or amphetamines), and disorders characterized by the chronic use of a drug, alcohol, or similar substance. Addiction and addictive…

Any disorder of recognition. Agnosia is a rare neurological condition in which an individual fails to recognize and identify persons or objects (see illustration). Typically, agnosia is the result of damage to specific areas of the brain.…

Mechanized systems of food and fiber production used in agriculture. The mechanized systems comprising agricultural machinery are utilized in numerous aspects of agriculture, including the initial tillage of the soil (Fig. 1), planting, cultural…

The repeated and/or excessive use of alcohol (ethanol) that continues despite negative physical, psychiatric, or social consequences. Alcoholism is characterized by consuming alcohol more often, in larger amounts, or over longer periods than…

An informal assemblage of predominantly aquatic eukaryotes that carry out oxygen-evolving photosynthesis, but lack specialized water-conducting and food-conducting tissues. Algae (Fig. 1) are eukaryotic organisms (having an organized nucleus).…

A small, tropical, evergreen tree (Pimenta dioica) and its dried, unripe fruit (berry). Allspice (Pimenta dioica; alternatively, P. officinalis) [see illustration] is a member of the myrtle family (Myrtaceae). Allspice, which is also known as…

A significant, yet relatively selective loss of memory. Amnesia is a type of memory loss, often resulting from brain disease or injury (see illustration). The inability to remember can be temporary or permanent. In general, amnesia can be…

A statistical technique that partitions the total variation in experimental data into components assignable to specific sources. Analysis of variance is applicable to data for which (1) effects of sources are additive, (2) uncontrolled or…

A disorder of language acquired as a result of brain disease. Aphasia is impairment in the use of spoken or written language caused by brain disorders (see illustration) that cannot be explained by paralysis or incoordination of the articulatory…

An impairment in the performance of voluntary actions despite intact motor power and coordination, sensation and perception, and comprehension. Apraxia is a neurological condition in which there is difficulty with skilled tasks or learned movements…

Any vegetable that is prevalent in Asian cuisines, but less well known in Western diets. Asian vegetables (Fig. 1), also referred to as Asian greens or oriental vegetables, are very important in Asian countries, but are not as popular in North…

A common psychiatric disorder (especially in children) characterized by attentional difficulties, impulsivity, and hyperactivity. Attention deficit hyperactivity disorder (ADHD) is a mental disorder marked by an individual's inability to pay…

Any of a class of plant growth substances (phytohormones or plant hormones) that have an essential role in coordination of many growth and developmental processes during the life cycle of plants, especially the ability to increase the rate of shoot…

A class of nonflagellate unicellular algae, commonly called diatoms, with boxlike silicified walls. Members of the algal class Bacillariophyceae are commonly termed diatoms (Fig. 1). Diatoms range in maximum dimension from 4 μm (0.00004 in.) to more…

Any of several leguminous plants, or their seeds, long utilized as food by humans or livestock. There are more than 40,000 varieties of beans, with only a small number of these being mass-produced for human or animal consumption. In particular,…

The drug as well as the plant known as deadly nightshade (Atropa belladonna). The belladonna plant (Atropa belladonna; see illustration) belongs to the nightshade family, Solanaceae, in the order Solanales. The plant is a coarse and poisonous…

A discipline that combines biology, mathematics, and computer science to acquire, store, analyze, and disseminate complex biological data. The term bioinformatics was coined by Paulien Hogeweg and Ben Hesper in the early 1970s to describe the "the…

Fungi that exhibit the natural phenomenon of bioluminescence (the ability of an organism to emit visible light). Bioluminescence is the emission of photons of visible light by living organisms via the chemical reaction of molecular oxygen (O2) with…

A major mental disorder in which there are lifelong episodes of both mania and depression; also known as manic-depressive illness. Bipolar disorder, also termed manic-depressive illness or manic depression, is characterized by sudden and often…

A mental health illness characterized by a compulsive or obsessive focus on a perceived flaw in appearance. Body dysmorphic disorder (often abbreviated BDD) is a psychiatric illness in which a person has a severe, excessive preoccupation with a…

A garden for the culture of plants collected chiefly for scientific, educational, and esthetic purposes. A botanical garden (see illustration) is an establishment in which various plants, including trees, are collected, cultivated, and grown for…

The branch of biological science that embraces the study of plants and plant life. Botany is the scientific study of plants (see illustration), encompassing investigations of plant anatomy, physiology, genetics, phylogeny, ecology, pathology, and…

A division that consists of small and relatively simple plants commonly known as mosses, peat mosses, granite mosses, liverworts, and hornworts. Members of the division Bryophyta are referred to as bryophytes (see illustration). These nonvascular…

In its simplest form, a vector is a directed line segment. Physical quantities, such as velocity, acceleration, force, and displacement, are vector quantities, or simply vectors, because they can be represented by directed line segments. The algebra…

A genus comprising yeasts that cause a variety of human diseases referred to as candidiasis. All Candida species are single-celled yeasts (fungal organisms) that are ovoid in shape and 3–5 μm in size, and they multiply by a process called budding.…

An order of flowering plants (angiosperms) including the mustard and caper families. The plant order Capparales contains various families of eurosid dicotyledons. Most notably, mustards, capers, and various ornamental plants (see illustration) are…

A member of a class of common pigments, typically of yellow, orange, or red hues, that serve in both light absorption and the protection against too much light in photosynthesis as well as in the vision process. Carotenoids comprise a class of…

A medium-sized, spreading evergreen tree (Anacardium occidentale), which is grown widely in the tropics for its kidney-shaped edible nuts (also called cashews) and the resinous oil in the shells of the nuts. Cashew trees, which are native to Brazil,…

A coarse, erect, annual herb plant, Ricinus communis, belonging to the spurge family (Euphorbiaceae). The castor plant (Ricinus communis) is a member of the spurge family (Euphorbiaceae) in the order Malpighiales. The plant varies greatly in height…

Any member of the grass family (Poaceae or Gramineae) that produces edible grains usable as food by humans and livestock. Cereals are important cultivated crops. Common cereals include rice, wheat, barley, oats, maize (corn), sorghum, rye, and…

A type of sweet or sour fruit of the Prunus genus, as well as the tree that bears the fruit. Cherry trees belong to the Prunus genus in the order Rosales, and the sweet and sour fruits of these trees are called cherries (Fig. 1). There are…

An evergreen shrub or small tree, particularly Cinnamomum verum, and the spice obtained from the plant's bark. The cinnamon plant (see illustration) is a member of the laurel family (Lauraceae) in the order Laurales. Native to Sri Lanka, the…

A large palm, Cocos nucifera, widely grown throughout the tropics and valuable for its fruit and fiber. The coconut (Cocos nucifera) belongs to the plant family Arecaceae. The name coconut can refer to the tree and its fruit. Usually found near the…

Any of various tropical trees belonging to the genus Cola. Members of the genus Cola (family Malvaceae, order Malvales), which are native to tropical Africa, are called cola trees (see illustration). In particular, two species, C. acuminata and C.…

A natural and extremely useful extension of the familiar real numbers. They can be introduced formally as follows. Consider the two-dimensional real vector space consisting of all ordered pairs (a1, a2) of real numbers. Geometrically this space can…

Any living or fossil member of the plant division Pinophyta, consisting chiefly of woody trees or shrubs that produce cones and evergreen needles. Conifers are predominantly cone-bearing, evergreen trees and shrubs belonging to the order Pinales, as…

A fiber obtained from the cotton plant Gossypium. The cotton plant (genus Gossypium, order Malvales; Fig. 1) has been used by humans for more than 5000 years. The fiber (cotton) obtained from this plant is the most widely used natural fiber because…

An unharvested crop grown to improve soil quality or enhance pest management. Increasing numbers of farmers plant cover crops as a means of conserving soil, enhancing subsequent production, and reducing off-farm inputs. The sustainable agriculture…

A curve traced in the plane by a point on a circle that rolls, without slipping, on a line. If the line is the x axis of a rectangular coordinate system, at whose origin O the moving point P touches the axis, parametric equations of the cycloid are…

A woody higher plant that regularly loses its leaves at the end of each growing season. Deciduous plants drop (shed) their leaves seasonally, most commonly during the fall (autumn). In general, the dropping of leaves occurs at the inception of an…

The deliberate conversion of forest to nonforest land that results in the long-term reduction of tree canopy below a minimum level. Deforestation, also known as land clearing, permanently eliminates forests to utilize the land for other purposes…

A heterogeneous affective disorder involving a depressed mood and/or a loss of interest in daily activities. The most common form of affective disorder is depression (also termed clinical depression) [Fig. 1]. A major depressive episode is defined…

A branch of mathematics that deals with intrinsic properties of curves and surfaces in three-dimensional Euclidean space. The intrinsic properties are those which are independent of the geometrical object's orientation or location in space. The…

In arithmetic and algebra, the process of finding one of two factors of a number (or polynomial) when their product and one of the factors are given. The symbol ÷ now used mostly in elementary English and American arithmetics to denote division…

Impairment of the ability to read. Developmental dyslexia, which is a learning disorder with a neurobiological basis, is characterized by unexpected difficulty in reading in children and adults who otherwise possess the intelligence and motivation…

The number e usually defined as the limit approached by the expression as n approaches infinity. If the given expression is expanded by the binomial theorem, and if one uses the theorem that the limit of the quotient of two polynomials of equal…

The biological study of insects that have a direct influence on humanity. Economic entomology is a subdiscipline of entomology (the biological science that deals with the investigation of insects) and focuses on the effects of insects on human…

The controlled induction of a grand mal seizure under anesthesia to treat individuals suffering from certain psychiatric illnesses. Electroconvulsive therapy (ECT; Fig. 1) was introduced as a treatment for psychiatric disorders by the Italian…

A major clade or natural group of plants, comprising the land plants. The members of the Embryobionta or Embryophyta are commonly termed embryobionts or embryophytes, and they constitute the land plants. Embryophytes form a well-marked clade (a…

A volatile, fragrant oil obtained from plants. Essential oils are distinguished from those known as fixed oils, which are mainly triglycerides of fatty acids. Essential oils have been obtained from thousands of plants (Fig. 1) and are designated and…

A former order of rosid flowering plants, division Magnoliophyta (Angiospermae), in the class Magnoliopsida (dicotyledons). The order Euphorbiales consisted of the large family Euphorbiaceae (with about 7500 species) and 3 small satellite families…

A plant that retains its green foliage throughout the year. An evergreen plant, or simply evergreen, is a tree, shrub, or plant whose leaves are not shed in the winter and instead remain green year-round. In contrast, deciduous trees and plants…

A method of quantitative multivariate analysis with the goal of representing the interrelationships among a set of continuously measured variables (usually represented by their intercorrelations) by a number of underlying, linearly independent…

Plants grown and harvested for food, feed, or industrial purposes. Farm crops may be roughly classified as follows: (1) food crops—the bread grains [wheat (see illustration) and rye], rice, sugar crops (sugarbeets and sugarcane), potatoes, and dry…

Materials added to the soil, or applied directly to crop foliage, to supply elements needed for plant nutrition, and the management of this nutrient application to sustain maximum plant growth and yield while minimizing environmental impacts of…

A plant grown for its fibrous material, which is used for many commercial purposes and for home industry. Many plants are grown as fiber crops because of their content or yield of fibrous material (see illustration), which is used in the manufacture…

In algebra, the term "field" is used to designate an algebraic system or structure containing at least two elements and having two binary rules of composition: addition and multiplication (that is, if a and b are any two elements of the field, then…

The segment of horticulture concerned with the commercial production, marketing, and sale of plants grown and used for decorative or display purposes. Floriculture is a branch of horticulture, that is, the art and science of growing plants,…

Any of the grasses and legumes that make up grasslands and are consumed by grazing livestock. Grasslands represent an ancient renewable natural resource. In general, grasslands form 25% of the world's vegetation and occupy the largest area of any…

The natural medium for growth of tree roots and associated forest vegetation. Proper forest growth and management depend on many factors, including the quality of the forest soil (see illustration). In general, weathering of underlying rock,…

The science, art, and practice of managing and using the natural resources that occur on and in association with forested lands. Forestry is the management of forested lands (see illustration). It involves the planning and implementation of…

A hypersensitivity or altered reactivity caused by fungal allergens. More than 20% of the population in industrialized countries suffers from allergic disease, and diverse allergens (substances foreign to the body that cause allergy) associated with…

A hardy perennial, Allium sativum, of Asiatic origin and belonging to the plant order Asparagales. Garlic is grown for its pungent bulbs (see illustration). Segments of these are used primarily for seasoning. Europeans have grown garlic for probably…

A branch of mathematics concerned with the properties of space, including points, lines, curves, planes and surfaces in space, and figures bounded by them. Multiple kinds of geometry exist, dealing with everyday concepts such as lengths, angles, and…

Soil ingestion by animals. Grazing animals such as sheep and cattle ingest varying amounts of soil when they graze herbage contaminated with it.Pastures become contaminated with soil when livestock walk across the herbage, particularly in wet…

A member of a family of diterpenoid carboxylic acids that are notable for being plant hormones. Gibberellins are diterpenoid carboxylic acids. Most of them possess ent-gibberellane or ent-20-norgibberellane carbon (C) skeletons. Gibberellins occur…

An important spice or condiment, and the plant (Zingiber officinale) from which it is obtained. The ginger plant, Zingiber officinale, is a member of the ginger family Zingiberaceae and is a native of southeastern Asia. The plant is an erect…

The common name for a group of perennial herbs in the genus Panax cultivated for the aromatic root of the plant, which is used medicinally in China. Herbal members of the genus Panax belong to the aralia family (Araliaceae) and are native to…

Any of the crop plants belonging to the grass family (Poaceae or Gra­mineae) that are generally grown for their edible starchy seeds. Grain crops are often referred to as cereal crops and include wheat, rice, corn (maize), barley (see illustration),…

The common name for plants of the genus Vitis characterized by climbing stems and grown for the edible, pulpy berries. Grapes (genus Vitis) comprise one of the world's most significant and economically important crops. The common grapevine is…

An evergreen tree (Citrus paradisi) and its edible citrus fruit. Grapefruit (Citrus paradisi) is a subtropical evergreen tree belonging to the order Sapindales. It has a well-rounded top and is cultivated for its large and globose citrus fruit. The…

Any member of the family Poaceae (Gramineae) cultivated as forage and grain for consumption. Grasses are arguably the most useful of all the plants that cover the Earth. The cereal grass crops [wheat (Fig. 1), rice, corn (maize), rye, barley, oats,…

A morphologically distinct cell that is found in the epidermis of terrestrial plant shoots and that functions in regulating stoma size. Guard cells are paired, crescent-shaped epidermal cells that regulate water loss and gas exchange in terrestrial…

A class of lower green plants called liverworts that belong to the division Bryophyta. The class Hepaticopsida, also called Marchantiopsida, comprises the liverworts, which are nonvascular land plants. Although there is a great diversity of external…

An intensively managed plant cultivated for food or for esthetic purposes. Plant agriculture is divided traditionally into the fields of agronomy (herbaceous field crops, mainly grains, forages, oilseeds, and fiber crops), forestry (forest trees and…

The collective techniques for supplying nutrients and water directly to the roots of plants, without soil or other media. Hydroponics is concerned with the cultivation and growing of plants without soil or other media. Hydroponic systems (Fig. 1)…

Any of several low, perennial, tropical South American shrubs or half-shrubs in the family Rubiaceae. Ipecac plants (also termed ipecacuanha plants) are native to the tropical forests of Brazil and Colombia. Several species are used, but the dried…

The artificial application of water to the soil to produce plant growth. Irrigation also cools the soil and atmosphere, making the environment favorable for plant growth. The use of some form of irrigation (Fig. 1) is well documented throughout the…

The removal of water from the surface of the land and the control of the shallow ground water table improves the soil as a medium for plant growth. The sources of excess water may be precipitation, snowmelt, irrigation water, overland flow or…

An order of flowering plants composed of seven eumagnoliid families of tropical tree and shrub species. The plant order Laurales, with approximately 2500–2800 species, contains numerous trees and shrubs having ecological significance. Members of the…

Citrus limon, a small evergreen tree belonging to the order Sapindales that is cultivated for its fruit. In commercial terms, the lemon (Citrus limon; order Sapindales) is the most important of the acid citrus fruits (see illustration). It probably…