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A variety of chalcedonic quartz that is distinguished by the presence of color banding in curved or irregular patterns (Fig. 1). Most agate used for ornamental purposes is composed of two or more tones or intensities of brownish-red, often…

A sodium-rich plagioclase feldspar mineral whose composition extends over the range Ab100An0 to Ab90An10, where Ab (= albite) is NaAlSi3O8 and An (= anorthite) is CaAl2Si2O8 (see illustration). Albite occurs in crustal igneous rocks as a major…

Most commonly, a generic name for all fossil resins, although it has been restricted by some to refer only to succinite, the mineralogical species of fossil resin that includes most of the Baltic Coast deposits. The time necessary to transform resin…

A lithium aluminum phosphate mineral of basic formula LiAl(PO4)(F). The structure of amblygonite consists of phosphate (PO4) groups of tetrahedra and AlO6 groups of octahedra. Each PO4 tetrahedron is connected to an AlO6 octahedron. Corner-sharing…

The transparent purple to violet variety of the mineral quartz. Although quartz is perhaps the commonest gem mineral known, amethyst (see illustration) is rare in the deep colors that characterize fine quality. Amethyst is usually colored unevenly…

An ongoing current event in which a large number of living species are threatened with extinction or are going extinct because of environmentally destructive human activities. The Earth is presently in the midst of a mass extinction event. In the…

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,…

A taxonomic order of insects comprising the cockroaches and termites. The order Blattodea, also referred to as Blattaria, contains at least 4500 species of cockroaches (Fig. 1) and 3000 species of termites. Previously, termites were assigned to a…

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…

The response of corals to environmental stress in which they eject the single-cell algae that live within the transparent coral tissue, making the white coral skeleton visible. Corals (Fig. 1) are animals that live in a partnership (symbiosis) with…

The common name for three living species of mammals in the family Elephantidae (order Proboscidea). Elephants are extant members of the mammalian family Elephantidae, which is one of several families included in the order Proboscidea. The remaining…

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…

Plants that have 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…

Commercially grown plants that have 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…

A species translocated from one region or continent to another outside its normal range, particularly when the translocation is the result of human activity (intentional or otherwise). Many thousands of species, including animals, plants, fungi,…

A rare mineral tectosilicate found in volcanic rocks high in potassium and low in silica. Kaliophilite is one of three polymorphic forms of KAlSiO4; the others are the rare mineral kalsilite and an orthorhombic phase formed artificially at about…

A mammalian order containing the egg-laying platypus and echidnas. Members of the order Monotremata (monotremes) are egg-laying mammals belonging to the subclass Prototheria (in some alternative classifications, the monotremes have been assigned to…

An order of placental mammals containing the largest and most powerful living terrestrial mammals—the elephants. Proboscideans once had a wide distribution, reaching every continent except Australia and Antarctica. Although early forms lacked both…

The planning and implementation of actions to establish, protect, restore, and maintain trees and forests in cities and smaller communities. When the field of urban forestry began in the 1960s, it focused on individual trees along streets and…

A nocturnal, burrowing, insectivorous, piglike mammal (Orycteropus afer) in the order Tubulidentata. The mammalian order Tubulidentata contains a single family, Orycteropodidae, and a single extant aardvark species, Orycteropus afer (Fig. 1).…

A branch of meteorology that examines the effects and impacts of weather and climate on crops, rangeland, livestock, and various agricultural operations. Agricultural meteorology, or agrometeorology, addresses topics that often require an…

The pure and applied science that is concerned with botany and management of crop and ornamental plants for utilization by humankind. As it relates to plants, agricultural science concerns itself with the application of scientific methods to…

The art and science of crop and livestock production. In its broadest sense, agriculture comprises the entire range of technologies associated with the production of useful products from plants and animals, including soil cultivation, crop and…

The science and study of crops and soils. Agronomy is the umbrella term for a number of technical research and teaching activities (see illustration): crop physiology and management, soil science, plant breeding, and weed management frequently are…

Natural and artificial substances in the atmosphere that affect human health or well-being, or the well-being of any other organisms in the environment. Air pollution also applies to situations in which contaminants affect structures and artifacts…

A natural process in which harmful or beneficial effects are caused by secondary metabolites that spread from a donor organism to a recipient and are produced by plants, algae, bacteria, and fungi. Allelopathy is a key ecological process and has…

One of the major classes composing the superclass Tetrapoda of the subphylum Vertebrata, and including frogs, toads, salamanders, and caecilians. Amphibians, that is, members of the class Amphibia, are tetrapod vertebrates. Modern amphibians number…

Any living organism taxonomically assigned to the classification kingdom known as Animalia. Members of the kingdom Animalia—that is, animals (see illustration)—possess certain characteristics that distinguish them from organisms belonging to the…

A discipline within the field of animal behavior that focuses on the reception and use of signals. Animal communication could well include all of animal behavior because a liberal definition of the term signal could encompass all stimuli perceived…

The group of primates most closely related to humans. The primates included in the ape group are the African great apes, the gorillas (Fig. 1) and chimpanzees; the Asian great apes, the orangutans; and the lesser apes from Asia, the gibbons. Humans…

A deciduous tree (genus Malus) in the order Rosales, which produces an edible, simple, fleshy, pome-type fruit. Apples (Fig. 1) belong to the family Rosaceae, which includes many other deciduous fruits, including pears, peaches, and cherries. There…

An order of leeches (subclass Hirudinida) characterized by the absence of a protrusible proboscis and including both blood-feeding and macrophagous (predatory) varieties. Most notorious among the blood-feeding leeches in the Arhynchobdellida is the…

Vegetables that are 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 America…

A class of the asterozoan group of the phylum Echinodermata, often known as sea stars or starfish. Members of the class Asteroidea, that is, asteroids, are notable echinoderms with a star-shaped body plan (Fig. 1). Unlike members of their sister…

A large tropical plant of the genus Musa and its edible fruit. The banana belongs to the family Musaceae (order Zingiberales). The banana of commerce (Musa acuminata), which is believed to have originated in the Asian tropics, was one of the…

Any member of the mammalian family Ursidae, which contains the largest terrestrial carnivores. The bear family Ursidae comprises a number of carnivorous mammalian species. There are eight extant species of bears in three subfamilies: Ursinae…

The management and maintenance of colonies of honeybees for human purposes. Beekeeping is an ancient art. Although the commonly known honeybee species (Fig. 1) is native to Europe and Africa, humans have transported them to other continents. The…

The study of behavior change in response to drugs, chemicals, or other environmental conditions or agents. Behavioral toxicology investigates the effect of toxic exposure on organismal behavior. The toxic exposure can involve various chemicals,…

The destruction of organic compounds by microorganisms. Biodegradation is a process (carried out by microorganisms) that decomposes organic material into its constituent elements or new compounds. Microorganisms, particularly bacteria (and fungi to…

A microbial (often bacterial) community that is enveloped by an adhesive substance (the glycocalyx) at the interface of a liquid and a surface. Biofilms (see illustration) are defined as highly structured communities of microorganisms that are…

The study of the cycling of chemicals between organisms and the surface environment of the Earth. The chemicals either can be taken up by organisms and used for growth and synthesis of living matter or can be processed to obtain energy. The chemical…

The use of parasitoids, predators, and pathogens to reduce injurious pest insect populations and consequently the damage that they cause. Biological insect control (or insect biocontrol) is the regulation of insect populations by biological means.…

One of the main extant classes in the phylum Mollusca. Members of the molluscan class Bivalvia (formerly, Pelecypoda) are known commonly as bivalves and include clams, oysters, mussels, and scallops. All bivalves are aquatic, living at all depths of…

A biennial umbellifer (Daucus carota) of Asiatic and Mediterranean origin belonging to the plant order Apiales. The carrot (Daucus carota; Fig. 1) is grown for its edible roots, which are eaten raw or cooked. Cultivated forms of the root vegetable…

An aquatic mammalian order comprising approximately 90 living species of whales, dolphins, and porpoises and their fossil relatives. Like all other mammals, members of the order Cetacea (cetaceans) nurse their young with milk produced by the mother,…

The common name for numerous species of small to medium-sized lizards that comprise the family Chamaeleonidae (also Chamaeleontidae). Chameleons (see illustration) are members of the family Chamaeleonidae (also Chamaeleontidae) in the order Squamata…

System behavior that depends so sensitively on the system's precise initial conditions that it is, in effect, unpredictable and cannot be distinguished from a random process, even though it is deterministic in a mathematical sense. This article…

An order of the class Reptilia, including the turtles, terrapins, and tortoises; also termed Testudines. The order Chelonia (often referred to as Testudines) comprises one of the oldest groups of reptiles on Earth. Members of the Chelonia…

A group of trees belonging to the madder family (Rubiaceae), occurring indigenously in the cool, cloud forests of the Andes from Colombia to Peru. Many species of cinchona (genus Cinchona) have been described. Most are variants of C. pubescens (see…

The long-term records of precipitation, temperature, wind, and all other aspects of the Earth's climate. Climate, like the Earth itself, has a history extending over several billion years. Climatic changes have occurred at time scales ranging from…

Construction of a mathematical model of the climate system of the Earth capable of simulating its behavior under present and altered conditions. The Earth's climate is continually changing over time scales ranging from hundreds of years to a few…

The scientific study of climate. Climate is the expected mean and variability of the weather conditions for a particular location, season, and time of day. The climate is often described in terms of the mean values of meteorological variables such…

Management of the human use of natural resources to provide the maximum benefit to current generations while maintaining capacity to meet the needs of future generations. Conservation includes both the protection and rational use of natural…

A calcarenite or clastic limestone whose detrital particles are chiefly fossils, whole or fragmented. The term coquina is most frequently used for an aggregate of large shells more or less cemented by calcite (see illustration). If the rock consists…

Pathological conditions affecting the health of coral and causing its physiological dysfunction. Broadly defined, coral disease (Fig. 1) is any impairment to coral health resulting in physiological disturbance and breakdown. It usually involves…

A measure of the three-dimensional structure of live coral communities on reefs. Coral reef structural complexity is an intrinsic element of coral reef ecosystems and quantitates the surface area of coral in relation to its linear area. The…

An acceleration which arises as a result of motion of a particle relative to a rotating system. Only the components of motion in a plane parallel to the equatorial plane are influenced. Coriolis accelerations are important to the circulation of…

A large, tawny brown wild cat, Puma concolor (family Felidae), once widespread over most of the Americas; also known as catamount, mountain lion, painter, and puma. The cougar (Puma concolor; see illustration) is a carnivorous member of the family…

An extremely diverse, species-rich group of arthropods that have inhabited marine environments since the beginning of the Cambrian Period. Crustacea is a notable taxon of invertebrates. Common members of the Crustacea, that is, crustaceans, are…

A class of the phylum Cnidaria, comprising the box jellyfish. Members of the Cubozoa are commonly known as box jellyfish or cubozoans. These cnidarian invertebrates are good swimmers, and their distribution is mostly tropical and subtropical. There…

A vortex in which the sense of rotation of the wind about the local vertical is the same as that of the Earth's rotation. Thus, a cyclone rotates clockwise in the Southern Hemisphere and counterclockwise in the Northern Hemisphere. In meteorology…

A vertical sequence of several different kinds of distinctive sedimentary rock units that is repeated upward through the stratigraphic succession. Originally defined in the rock succession of Pennsylvanian age in the Illinois Basin in the 1930s, the…

Equipment used in the production and processing of milk and milk products, including milking machines, cream separators, coolers, pasteurizers, homogenizers, butter-making equipment, evaporators and dryers, and related items of equipment. Dairy…

A general term for a genus of tall forage grasses, of which the most important species is the deeply rooted perennial Paspalum dilatatum. Dallis grass (see illustration) is widely grown in the southern United States, mostly for pasture, and remains…

Common name for the plant Colocasia esculenta, including the variety antiquorum (taro). Dasheen plants are among the few edible members of the aroid family (Araceae). Native to southeastern Asia and Malaysia, the plants supply local inhabitants with…

The date palm, Phoenix dactylifera, which is one of the oldest cultivated tree crops. The date palm provides a staple food for many populations in the Middle East and North Africa and is also highly valued for feed, fiber, and shelter. Beginning in…

One of the more highly specialized crustacean orders. Members of the order Decapoda, termed decapods, are prominent crustaceans (superorder Eucarida; class Malacostraca; subphylum Crustacea; phylum Arthropoda), including shrimps, crayfish, lobsters,…

The name for any four-legged, hoofed, grazing animal in the mammalian family Cervidae. Deer are ruminant, even-toed ungulates (hoofed mammals) belonging to the order Artiodactyla. As members of the family Cervidae, they also are known as cervids. In…

Defoliants are chemicals that cause leaves to drop from plants; defoliation facilitates harvesting. Desiccants are chemicals that kill leaves of plants; the leaves may either drop off or remain attached; in the harvesting process the leaves are…

The division of forestry concerned with taxonomy of trees and other woody plants. The term dendrology is derived from the Ancient Greek: dendron (= tree) and -logia (= study of or science of); the term xylology is used occasionally to denote the…

A genus of tropical shrubs belonging to the legume family [Leguminosae (Fabaceae)]. Plants of the genus Derris (see illustration), with their long branches climbing over other vegetation, occur as members of the jungle undergrowth in Southeast Asia,…

An order of nematodes in which the variable stoma may or may not be armed with a dorsal tooth that may or may not be opposed by subventral denticles. The variable amphids (anterior sensory receptors) range from reniform to elongate loops to simple…

An order of nematodes in which the taxa are readily recognized by their conspicuous body annulation. The annuli of members of the order Desmoscolecida may be covered with concretion rings, or the cuticle may be ornamented with scales, warts, or…

An order of sea urchins (class Echinoidea) possessing an aulodont Aristotle's lantern (jaw apparatus) with unkeeled teeth that are U-shaped in cross section, and with the apophyses not meeting at the top of the lantern. In Diadematoida, the…

A large group of flukes (parasitic flatworms) within the class Trematoda, with some thousands of described and probably many thousands of not yet described species. The Digenea range from about 0.2 mm (0.008 in.) to over 1 m (3.3 ft) in length. They…

An annual culinary herb, genus Anethum, of the carrot family, Apiaceae (Umbelliferae). Dill supplies four products: dill seed oil, dill leaf oil, dill seed, and dill leaf. Although all dill grown in the United States is one species, Anethum…

The monoclinic pyroxene mineral which in pure form has the formula CaMgSi2O6. Its space group is C2/c. Pure diopside melts congruently at 1391°C (2536°F) at atmospheric pressure; the effect of pressure up to 50 kilobars (5 gigapascals) on its…

Skin diving, or diving without the aid of special equipment, is a technique to investigate underwater environments and to gather shellfish or other items of commercial importance. In breath-hold diving, fins and faceplate are usually employed to…

Members of the carnivorous mammalian family Canidae. All breeds of domestic dogs (Fig. 1), the wild dogs, and related species belong to the family Canidae. Despite the various breeds of domestic dogs that are known, the scientific name for all types…

Any of the tree or shrub species in the genus Cornus. The tree, Cornus florida, also known as the flowering dogwood, may reach a height of 40 ft (12 m) and is found in the eastern half of the United States and in southern Ontario, Canada. It has…

The carbonate mineral CaMg(CO3)2. Dolomite is a very common mineral, occurring in a variety of geologic settings. It is often found in ultrabasic igneous rocks, notably in carbonatites and serpentinites, in metamorphosed carbonate sediments, where…

A type of convective transport in fluids that depends on the difference in diffusion rates of at least two density-affecting components. This phenomenon was discovered in 1960 in an oceanographic context, where the two components are heat and…

A large coniferous tree, Pseudotsuga menziesii (formerly, P. taxifolia), known also as red fir, belonging to the pine family (Pinaceae). Douglas-fir is one of the most widespread and most valuable tree species of western North America and ranks…

A nesosilicate mineral with composition Al7(BO)3(SiO4)3O3. Dumortierite crystallizes in the orthorhombic system but well-formed crystals are rare; the mineral usually occurs in parallel or radiating fibrous aggregates. There is one direction of poor…

Plants occupying sand dunes and the slacks, or swales, and flats between them. The density and diversity of dune vegetation are greater on coastal dunes than on desert dunes. Dune Plant geography Sand Zonation A zonation pattern is evident in the…

A state of fluid flow in which the distribution of mass and momentum is unstable. Fluid flows are subject to a variety of instabilities which generally cause the flow to become more complex and which often lead to turbulent, chaotic flow.…

The low-density outermost layer of the Earth above the Mohorovičić discontinuity (the Moho), a global boundary that is defined as the depth in the Earth where the compressional-wave seismic velocity increases rapidly or discontinuously to a value in…

Any tree of the genus Diospyros of the ebony family, containing more than 250 species. Some species of ebony are important for their succulent fruits, such as date plum, kaki plum, and persimmon, and several are important for timber, particularly…

The biological sonar that bats, toothed whales, and certain other animals use to navigate without the visual system. Echolocation, or biosonar, is the physiological process that certain animals use to locate objects by reflected sound, primarily in…

The interaction of at least two organisms or species such that, for each, the birth or growth rates are depressed and the death rate increased by the presence of the other organisms or species. Ecological competition is the conflict that arises…

The study of the flow of energy within an ecological system from the time the energy enters the living system until it is ultimately degraded to heat and irretrievably lost from the system. It is also referred to as production ecology, because…

The methods required for the measurement of features of plant and animal populations or for quantifying energy flow or other aspects of ecological communities. Ecologists are concerned with such a wide range of variables that they may use many other…

The use of computer simulations or mathematical equations to address questions that cannot be answered solely by experiments or observations. Ecological models have two major aims: to provide general insight into how ecological systems or ecological…

A directional change in an ecological community. Populations of animals and plants are in a dynamic state. Through the continual turnover of individuals, a population may expand or decline depending on the success of its members in survival and…

The study of insects that have a direct influence on humanity. Though this includes beneficial as well as harmful species, most attention is devoted to the latter and how they become pests and are controlled. The emphasis on managing harmful insects…

An obligate association formed between the roots of many plant species, especially trees, and a diverse range of soil fungi. The fungi and the finest, terminal root tips interact to form joint organs called ectomycorrhizas (Fig. 1). In…

A fish in the order Anguilliformes (true eels), one of several orders of the superorder Elopomorpha, which share a leptocephalus (a slender, transparent larva with a long narrow) [Fig. 1] stage. The name eel also applies to other fishes similar in…

A warm-season vegetable (Solanum melongena) of Asiatic origin belonging to the plant order Solanales (formerly Polemoniales). Eggplant is grown for its usually egg-shaped flesh fruit (see illustration), which is eaten as a cooked vegetable. Cultural…

A disruption of the usual tropical Pacific Ocean and atmospheric circulation patterns that includes a few seasons of warmer-than-normal sea-surface temperatures in the central and eastern equatorial Pacific Ocean, weaker mid-Pacific trade winds, and…

The effect of changes in pressure and temperature on electrical properties of rocks. There has been increasing interest in the electrical properties of rocks at depth within the Earth and the Moon. The reason for this interest has been consideration…