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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…

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.…

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 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 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…

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…

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,…

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…

An integrated device consisting of a biological recognition element and a transducer capable of detecting the biological reaction and converting it into a signal that can be processed. Ideally, the sensor should be self-contained, so that it is not…

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…

The measurement of the quantity of heat transferred during chemical reactions, changes of state, mixing of substances, as well as other chemical and physical processes. The unit of energy in the International System of Units is the joule, symbolized…

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…

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…

A cycloaddition reaction between a diene and a dienophile. The simplest Diels-Alder reaction (O. Diels and K. Alder, 1928) occurs between butadiene and ethylene and is often referred to as a [4+2] cycloaddition. The numbers, four and two in…

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 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 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…

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,…

Hypersensitivities or altered reactivities 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…

Members 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 in…

The discovery, development, and application of sustainable chemical reactions that create no waste or generate only benign wastes. The idea that toxic chemicals, once created, can be contained or prevented from entering the environment is…

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…

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…

Solvent removal from the frozen state by sublimation; commonly referred to as freeze-drying. In lyophilization, the dried material, a porous solid, is sealed under vacuum or inert-gas (liquid nitrogen) atmosphere and retains its physical and…

One of the largest orders of the rosid eudicotyledons. The order Malpighiales is an important flowering plant group with a worldwide distribution. Depending on the classification, it contains approximately 35 to 40 families, totaling about 16,000…

A solid or liquid (molten), opaque material with a lustrous surface and good electrical and thermal conductivities. Solid metal is usually crystalline and ductile and can be permanently deformed by shear on crystal planes (Fig. 1); permanent…

A delicately flavored spice obtained from the nutmeg tree (Myristica fragrans), a native of the Moluccas (Maluku Islands or Spice Islands). The nutmeg tree is a dark-leafed evergreen that can reach 9–18 m (30–60 ft) in height and is a member of the…

An order of flowering plants that have previously been included in the subclass Magnoliidae. Deoxyribonucleic acid (DNA) sequence studies have demonstrated that Nymphaeales as previously defined contain two families, Ceratophyllaceae (water…

A genus (Quercus) of trees, some of which are shrubby, with about 200 species, mainly in the Northern Hemisphere. About 50 species of oaks are native in the United States. All oaks have scaly winter buds, usually clustered at the ends of the twigs,…

An agricultural crop of the genus Avena grown for its grain and straw in most countries of the temperate zones of the world. Oats (Fig. 1) belong to the order Poales (Cyperales), family Poaceae (Gramineae), and genus Avena. The most important crop…

An order of filamentous freshwater green algae (Chlorophyceae) with unique morphological features including (1) an elaborate method of cell division that results in the accumulation of apical caps, (2) zoospores and antherozoids with a subapical…

One of the chemical senses, specifically the sense of smell. Olfaction comprises the action or capacity of smelling, and is a form of chemoreception (the ability of organisms to detect changes in the chemical composition of their exterior or…

Any plant of the genus Olea in the order Lamiales (alternatively Scrophulariales), especially O. europaea, which is cultivated for its drupaceous fruit. Olea europaea is a small to medium-sized evergreen tree (Fig. 1). Olive fruits, both ripe…

A cool-season biennial, Allium cepa, that is cultivated for its edible bulb. The onion is of Asiatic origin and belongs to the plant order Asparagales; it was formerly included in the order Liliales. Related species are leek (A. porrum), garlic (A.…

Any synthetic or semisynthetic organic chemical compound that resembles opium in its pharmacological action to reduce pain. An opioid is an organic chemical compound, created synthetically or semisynthetically, that duplicates the analgesic…

Any of various evergreen trees of the genus Citrus, cultivated for its edible fruit. Orange trees (genus Citrus) belong to the family Rutaceae of the order Sapindales. The various trees classified as orange trees are most notable for producing…

Any member of the plant family Orchidaceae, having complex, specialized irregular flowers usually with only one or two stamens. The orchid family, Orchidaceae, is among the largest families of plants and is estimated to contain more than 25,000…

An order of flowering plants, division Magnoliophyta (Angiospermae), in the order Asparagales (monocotyledons). The order Orchidales consists of four families: the Orchidaceae, with 20,000–25,000 species; the Burmanniaceae, with more than 100…

An herb, also known as wild marjoram. The dried leaves of several species of aromatic plants are known as oregano; thus, oregano is a common name for a general flavor and aroma rather than the name of a specific plant. MarjoramEuropean oregano…

The genus Maclura of the mulberry family, with one species, M. pomifera. The osage orange tree may attain a height of 60 ft (18 m) and has yellowish bark, milky sap, simple entire leaves, strong axillary thorns, and aggregate green fruit that are…

A chemical reaction in which some composition variable of a chemical system exhibits regular periodic variations in time or space. It is a basic tenet of chemistry that a closed system moves inexorably toward an unchanging state called chemical…

An order of flowering plants (angiosperms) in the eurosid I group of the rosid dicots. The order is previously unrecognized in classifications of the angiosperms, but is indicated by numerous studies of DNA sequences. Oxalidales consist of five…

An order of monocotyledons, the composition of which only recently has been revealed by deoxyribonucleic acid (DNA) sequence studies of four genes. Included are four families, two of which have been generally viewed as closely related: Pandanaceae…

An order of flowering plants, division Magnoliophyta (Angiospermae), in the subclass Magnoliidae of the class Magnoliopsida (dicotyledons). The order Papaverales consists of two families: Papaveraceae, with approximately 200 species; and…

Carica papaya, a semiwoody, usually single-stemmed, herbaceous plant cultivated for its fruit in tropical and subtropical regions. The papaya plant (Fig. 1) originated along the Caribbean lowlands of Mesoamerica and is now extensively and…

A type of pepper, Capsicum annuum, with nonpungent flesh, grown for its long red fruit. The paprika pepper (see illustration) is a member of the plant order Solanales (formerly assigned to Polemoniales) and is of American origin. It is most popular…

An annual leafy leguminous vine, Pisum sativum (order Fabales), cultivated for its smooth or wrinkled, round edible seeds, which are borne in dehiscent pods. The garden pea (Fig. 1) is one of the world's oldest cultivated crops. It is a native of…

A deciduous fruit tree species, Prunus persica, of the order Rosales. The peach (see illustration), taxonomically known as Prunus persica (order Rosales), is a notable fruit tree species that originated and was first cultivated in western China. It…

A long-season cultivar (cultivated variety) of muskmelon, Cucumis melo, of the gourd family. Persian melons (see illustration) are members of the family Cucurbitaceae (which includes melons, squashes, pumpkins, and cucumbers) in the order…

A deciduous fruit tree species, Diospyros kaki, in the ebony family (Ebenaceae). Persimmon trees (Fig. 1) originated in the subtropical regions of China, but were cultivated more extensively in Japan. At the present time, China, South Korea, and…

A class of plants, commonly called brown algae, in the chlorophyll a-c phyletic line (Chromophycota). Brown algae occur almost exclusively in marine or brackish water, where they are attached to rocks, wood, sea grasses, or other algae.…

In physical chemistry, the various situations in which two or more phases (or states of aggregation) can coexist in thermodynamic equilibrium with each other, with the nature of the transitions between phases, and with the effects of temperature and…

The principal food-conducting tissue in vascular plants. The long-distance transport of nutrients in plants occurs in the phloem, which is a highly specialized tissue that links all the organs of the plant. The conducting cells of phloem are known…

The first step in the long-distance transport of nutrients in plants. Phloem loading also provides the driving force for this transport. Why is long-distance transport needed? Although vascular plants produce their own organic molecules by…

The regulatory effect of light on plant form, involving the growth, development, and differentiation of cells, tissues, and organs. Morphogenic influences of light on plant form are quite different from the light effects that nourish the plant…

The growth, development, or other responses of organisms to the length of night or day, or both. Photoperiodism has been observed in plants and animals, but not in bacteria (prokaryotic organisms), other single-celled organisms, or…

Any plant mechanism that serves to prevent photodamage, that is, damage caused by light. A cascade of mechanisms at different scales contributes toward photoprotection in plants: (1) preemptive reduction of the absorption of potentially harmful…

Light-dependent carbon dioxide release and oxygen uptake in photosynthetic organisms caused by the fixation of oxygen instead of carbon dioxide during photosynthesis. When the reactions of photosynthesis use oxygen instead of carbon dioxide,…

A plant photoreceptor specifically receptive to UV-A/blue light. Growth and development of plants are dependent on sunlight. Consequently, plants have evolved a sophisticated array of photoreceptor systems to control their growth. Phototropins are…

Any member of a class of intensely colored pigments found in some algae that absorb light for photo­synthesis. Phycobilins are open-chain tetrapyrroles structurally related to mammalian bile pigments, and they are unique among photosynthetic…

Natural substances that are toxic to microbial pathogens and are synthesized by plants as a defensive response to infection. Phytoalexins comprise an important group of natural compounds manufactured by plants in response to pathogenic intrusions…

A photoreceptor (protein pigment) used by plants and other photosynthetic organisms to detect light. Phytochromes are protein-pigment photoreceptors (Fig. 1) that control most photomorphogenic responses in various biological organisms that utilize…

Any tree of the genus Pinus, of the family Pinaceae, characterized by evergreen leaves, usually in tight clusters (fascicles) of two to five, rarely single. There are about 80 known species of pine distributed throughout the Northern Hemisphere.…

The edible seed of more than a dozen species of evergreen cone-bearing trees in the genus Pinus, native to the temperate zone of the Northern Hemisphere. The important pine nut–producing species are the stone pine (P. pinea) of southern Europe; the…

One of the major divisions of the seed plants. The most familiar and common representatives of the division Pinophyta are the evergreen, cone-bearing trees of the order Pinales (within the class Pinopsida). Members are known colloquially as…

The single class of the division Pinophyta (Gymnospermae). The class Pinopsida contains both living and fossil taxa. The living representatives of the Pinopsida are woody plants; most are trees with a central axis and excurrent branches. Leaves are…

A small order of flowering plants (3600 species) in the eumagnoliid group, which is composed of three anomalously woody vines (shrubs) or herbaceous families—the pipeworts (Aristolochiaceae), the black pepper family (Piperaceae), and the lizard's…

The psychological property of sound characterized by highness or lowness. Pitch is one of the two major auditory attributes of simple sounds, the other being loudness. Simple and complex sounds A simple sound source, such as a tuning fork, produces…

Any of various insectivorous plants of the families Sarraceniaceae and Nepenthaceae. In pitcher plants, the leaves form deep cups or pitchers in which water collects. Visiting insects, falling into this water, are drowned and digested by the action…

The central zone of tissue of an axis in which the vascular tissue is arranged as a hollow cylinder. Pith is present in most stems and in some roots (Fig. 1). Stems without pith rarely occur in angiosperms but are characteristic of psilopsids,…

The area of plant science concerned with the internal structure of plants. It deals both with mature structures and with their origin and development.Plant anatomists dissect the plant and study it from different planes and at various levels of…

Movement of signals or cues, chemical in nature, among individual plants or plant parts. Plant communication is a phenomenon of chemical ecology (see illustration). In particular, chemical cues or signals are released by plants in response to damage…

Proteins to which hormones bind, triggering responses in the target cells that express the receptors. There are basically five plant hormone classes: abscisic acid, auxin, cytokinin, gibberellin, and ethylene. All of these are simple organic…

The reproductively incompetent juvenile vegetative phase of seed plants, often with morphological and physiological characteristics that differ from those of an adult plant. The development of the aboveground portion of seed plants, also called the…

Artificial analytical constructs for identifying plants. The identification, nomenclature, and classification of plants are the domain of plant taxonomy, and one basic responsibility of taxonomists is determining if the plant at hand is identical to…

The worldwide array of plant life, including plants that have roots in the soil, plants that live on or within other plants and animals, plants that float on or swim in water, and plants that are carried in the air. Fungi used to be included in the…

The generally accepted system of naming plants. The study of plant variation and kinds leads to classification—the grouping of individual plants, the grouping of the groups, and the organizing of the groups (taxa) into ranks. Nomenclature deals with…

Plant parts having rather distinct form, structure, and function. Plant organs are the key anatomical features of plants. They include the aboveground leaves, stems, and reproductive structures of the plant's shoot system, as well as the belowground…

The arrangement of conducting elements which serves for two-way transportation of substances between different parts of a plant. The conducting elements are of two principal kinds: xylem, which is mainly responsible for the conduction of water…

The deliberate, directed reproduction of plants using plant cells, tissues, or organs. Plant propagation is the planned operation of creating new plants through natural or artificial means. In general, plant propagation can be accomplished by using…

A plant cell in which the cell wall has been removed. Although the plant cell is the basic unit of structure and function in plants, the term protoplast has been used to describe the organized entity of the living components of the plant cell that…

The area of study focusing on the development of a classification system, or taxonomy, for plants based on their evolutionary relationships (phylogeny). The assumption is that if classification reflects phylogeny, reference to the classification…

Aggregations of similar plant cells that perform a specific function for the plant. Plant tissue systems are the structural and functional tissue systems of plants. These tissue systems are organized into three entities: the dermal tissue system,…

Plant pathogens that are of viral or viroid origin. Plant viruses are pathogens that are composed mainly of a nucleic acid (genome) normally surrounded by a protein shell (coat); they replicate only in compatible cells, usually with the induction of…

An order of flowering plants, division Magnoliophyta (Angiospermae), in the subclass Asteridae of the class Magnoliopsida (dicotyledons). The order consists of only the family Plantaginaceae, with about 250 species. Within its subclass the order is…

Any of various smooth-skinned stone fruits grown on shrubs or small trees (genus Prunus, order Rosales). Plums are widely distributed in all land areas of the North Temperate Zone, where many species and varieties are adapted to different climatic…

An order of flowering plants, division Magnoliophyta (Angiospermae), in the subclass Caryophyllidae of the class Magnoliopsida (dicotyledons). The order consists of only the family Plumbaginaceae, with about 400 species. The plants are herbs or less…

An order of flowering plants (angiosperms) that includes the bromeliads, grasses, restios, rushes, and sedges. It comprises approximately 18 families and more than 18,000 species, over half of which are grasses (Poaceae). These families in general…

An order of flowering plants, division Magnoliophyta (Angiospermae), in the subclass Rosidae of the class Magnoliopsida (dicotyledons). The order consists of only the family Podostemaceae, with about 200 species, the greatest number occurring in…

The small male reproductive bodies produced in the pollen sacs of seed plants (gymnosperms and angiosperms) [Fig. 1]. The term comes unchanged from Latin, meaning fine dust or flour, and was popularized by Carl Linnaeus in 1751 (but used since…

An order of flowering plants, division Magnoliophyta (Angiospermae), in the subclass Rosidae of the class Magnoliopsida (dicotyledons). The order consists of 7 families and nearly 2300 species, mostly of tropical and subtropical regions. The vast…

A former order of flowering plants, division Magnoliophyta (Angiospermae) of the class Magnoliopsida (dicotyledons), reassigned to the suborder Polygonineae in the order Caryophyllales. The order Polygonales was considered as an ordinal grouping in…