Gabbro: Any of several medium- or coarse-grained rocks that consist primarily of Plagioclase feldspar and Pyroxene. Gabbros are found widely on the Earth and on the Moon. They are sometimes quarried for dimension stone (“black granite”), but the direct economic value of gabbro is minor. Far more important are the nickel, chromium, and platinum minerals that occur almost exclusively in association with gabbroic or related rocks. Magnetite (iron) and ilmenite (titanium) are also found in gabbroic complexes.
Galaxy: Any of the billions of systems of Stars and interstellar matter that make up the Universe. Galaxies vary considerably in size, composition, structure, and activity, but nearly all are arranged in groups, or clusters, containing from a few galaxies to as many as 10,000. Each is composed of millions to trillions of stars; in many, as in the Milky Way Galaxy, Nebulae can be detected. A large fraction of the bright galaxies in the sky are spiral galaxies, with a main disk in which spiral arms wind out from the centre. The arms contain the greatest concentration of a spiral galaxy’s interstellar gas and dust, where stars can form. Surrounding the centre (nucleus) is a large, usually nearly spherical nuclear bulge. Outside of this and the disk is a sparse, more or less spherical Galactic Halo. In elliptical galaxies, which vary greatly in size, stars are distributed symmetrically in a spherical or spheroidal shape. Dwarf ellipticals (with only a few million stars) are by far the most common kind of galaxy, though none is conspicuous in the sky. Irregular galaxies, such as the Magellanic Clouds, are relatively rare. Radio galaxies are very strong sources of radio waves. Seyfert galaxies, with extremely bright nuclei, often emit radio waves and may be related to Quasars.
Gall: Abnormal, localized outgrowth or swelling of plant tissue caused by infection from bacteria, fungi, viruses, or nematodes, or by irritation by insects and mites. The common plant disease crown gall, characterized by the proliferation of galls on the roots and lower stems, is caused by the bacterium Agrobacterium tumefaciens.
Gallery: A passage or burrow, excavated by an insect under bark or in wood for feeding or egg laying purposes
Galvanizing: Protection of Iron or Steel against exposure to the atmosphere and consequent rusting by application of a zinc coating. Properly applied, galvanizing may protect from atmospheric Corrosion for 15–30 years or more. If the coating is damaged, the iron or steel continues to be protected by sacrificial corrosion, a phenomenon in which atmospheric oxidation spares the iron and affects the zinc (as long as it lasts).
Game reserves: A game reserve is an area where hunting and shooting of wild animals is not allowed except under a special permit. The permit may specify the maximum number of animals or birds that may be killed or trapped, and the area and duration for which such permit is valid.
Gametophyte: In certain plants, the sexual phase (or an individual representing the phase) in the alternation of generations. The alternate, nonsexual phase is the Sporophyte. In the gametophyte phase, male and female organs (gametangia) develop and produce eggs and sperm (gametes), which unite in fertilization (syngamy). The fertilized egg (zygote) develops into the sporophyte, which produces numerous single-celled spores, which in turn develop directly into new gametes.
Gamma ray: Penetrating very short-wavelength Electromagnetic radiation, similar to an X-ray but of higher energy, that is emitted spontaneously by some radioactive substances. Gamma radiation also originates in the decay of certain subatomic particles and in particle-antiparticle annihilation. Gamma rays can initiate nuclear fission, can be absorbed by ejection of an electron, and can be scattered by free electrons.
Garden: Plot of ground where herbs, fruits, flowers, vegetables, or trees are cultivated. The earliest surviving detailed garden plan is Egyptian and dates from about 1400 BC; it shows tree-lined avenues and rectangular ponds. Mesopotamian gardens were places where shade and cool water could be enjoyed; Hellenistic gardens were conspicuously luxurious in their display of precious materials, a tradition carried over by Byzantine gardens. Islamic gardens made use of water, often in pools and fed by narrow canals resembling irrigation channels. In Renaissance Europe, gardens reflected confidence in human ability to impose order on the external world; Italian gardens emphasized the unity of house and garden. French 17th-century gardens were rigidly symmetrical, and French cultural dominance in Europe popularized this style into the next century. In 18th-century England, increasing awareness of the natural world led to the development of “natural” gardens that made use of irregular, nonsymmetrical layouts. Chinese gardens have generally harmonized with the natural landscape, and have employed rocks gathered from great distances as a universal decorative feature. Early Japanese gardens imitated Chinese principles; later developments were the abstract garden, which might feature only sand and rocks, and miniature gardens made in trays (See Bonsai).
Gardening: Laying out and tending of a garden. Though palatial gardens existed in ancient times, small home gardens became prevalent only in the 19th century. Gardening as a pastime grew with the increase in home ownership and leisure time. A well-designed flower garden displays blends and contrasts of colours and forms, and it takes into account the effect of seasonal changes. Essential tasks include soil maintenance, water regulation, control of weeds, and protection of plants from pests and diseases. Though chemical fertilizers, pesticides, and herbicides are widely used, less-toxic organic supplements and pest controls, predatory insects, and hand-weeding have become increasingly popular.
Garter snake: Any of more than a dozen species of snakes (genus Thamnophis, family Colubridae) with a striped pattern that resembles a garter: usually one or three longitudinal yellow or red stripes, with checkered blotches between. Forms in which the stripes are obscure or lacking are called grass snakes. Found in gardens and vacant lots, garters are among the most common snakes from Canada to Central America. They are small (usually less than 24 in., or 60 cm, long) and harmless, though some will strike if provoked. They eat insects, earthworms, and amphibians.
Gas reservoir: In geology, a naturally occurring storage area, characteristically a folded rock formation, that traps and holds natural gas. The reservoir rock must be permeable and porous to contain the gas, and it has to be capped by impervious rock in order to form an effective seal and prevent the gas from escaping. Typical reservoir rocks are sedimentary and include sands, sandstones, arkoses, and fissured limestones and dolomites. In the U.S. and certain other countries, artificial gas reservoirs are being created from depleted oil and gas fields, particularly near salt domes and in sedimentary basins, to store gas during periods of low consumption for later use.
Gastropod: Any member of the class gastropoda, the largest group of Mollusks, including about 65,000 species. Gastropods, which include the snails, conchs, whelks, limpets, periwinkles, abalones, slugs, and sea slugs, are found worldwide, in marine, freshwater, and terrestrial environments. Gastropods typically have a large foot with a flat sole for crawling, a single coiled shell that covers the soft body, and a head that bears a pair of eyes and tentacles. However, they are so diverse that some forms lack shells, while animals in one genus have shells with two halves, like bivalves. Most feed by using a radula, a ribbon of small horny teeth that tear food into pieces. They may be herbivores, carnivores, predators, parasites, or filter feeders of plankton and detritus.
Gazelle: Any of numerous species of graceful Antelope (genus Gazella) found on open plains and arid lands from Mongolia to the Atlantic coast of North Africa and throughout eastern and central tropical Africa. Gazelles are 2–3 ft (60–90 cm) high at the shoulder. They range in herds that usually contain 5 to 10 individuals but may include several hundred. They are generally brown with white under parts and rump, and many have a horizontal dark band along each side. A light stripe runs down each side of the face. The horns have numerous raised rings and are variously shaped, but all are slightly upturned at the ends. Some species are considered endangered.
Gelatin: Animal protein substance having gel-forming properties, used primarily in food products. Derived from collagen, it is extracted by boiling animal skin and bones. It is commonly produced as granules or as a mix with added sugars, flavours, and colours. Immersed in a liquid, gelatin takes up moisture and swells, causing the mixture to solidify. It is used to make such foods as molded desserts, jellied meats, soups, candies, and aspics and to stabilize such emulsion and foam food products as ice cream and marshmallows. It is nutritionally an incomplete protein. It is also used in various pharmaceutical products.
Gender: In language, a grammatical category contrasting distinctions of sex or animateness. Gender marking may be natural, with linguistic markers of gender corresponding to real-world gender, or purely grammatical, with markers of gender in part semantically based and in part semantically arbitrary. In languages with grammatical gender, nouns are partitioned into sets. Membership of a noun in a set may be expressed by its form and/or by the forms of other parts of speech controlled by the noun. Closely related to gender systems in language are class systems, as in Bantu Languages, in which the number of sets into which nouns are partitioned is much larger, with distinct categories for things such as plants, animals, and tools, though, as with nouns in Romance and Germanic languages, assignment of most nouns to classes is semantically arbitrary.
Gene: Unit of heredity that occupies a fixed position on a chromosome. Genes achieve their effects by directing protein synthesis. They are composed of DNA, except in some viruses that contain RNA instead. The sequence of nitrogenous bases along a strand of DNA determines the genetic code. When the product of a particular gene is needed, the portion of the DNA molecule that contains that gene splits, and a complementary strand of RNA, called messenger RNA (mRNA), forms and then passes to ribosomes, where proteins are synthesized. A second type of RNA, transfer RNA (tRNA), matches up the mRNA with specific amino acids, which combine in series to form polypeptide chains, the building blocks of proteins. Experiments have shown that many of the genes within a cell are inactive much or even all of the time, but they can be switched on and off. mutations occur when the number or order of bases in a gene is disrupted. (See also Genetic Engineering, Genetics).
Gene flow: Introduction of genetic material (by interbreeding) from one population of a species to another, thereby changing the composition of the gene pool of the receiving population. The introduction of new characteristics through gene flow increases variability within the population and makes possible new combinations of traits. In humans, gene flow usually comes about through human migration.
Gene pool: The total of all genes carried by all individuals in an interbreeding population
Generation: The successive developmental stages from reproduction to reproduction, e.g., egg, larva, pupa, adult.
Gene therapy or gene transfer therapy: Introduction of a normal gene into an individual in whom that gene is not functioning, either into those tissue cells that normally express the gene (curing that individual only) or into an early embryonic cell (curing the individual and all future offspring). Prerequisites for each procedure include finding the best delivery system (often a virus) for the gene, demonstrating that the transferred gene can express itself in the host cell, and establishing that the procedure is safe. Diseases for which gene-therapy research is advanced include cystic fibrosis, Huntington’s disease, and familial hypercholesterolemia; research continues on its application for Alzheimer’s disease, breast and other cancers, and diabetes. Some aspects of gene therapy, including genetic manipulation and selection, research on embryonic tissue, and experimentation on human subjects, have aroused ethical controversy.
Genetic code: Sequence of Nucleotides in DNA and RNA that determines the amino acid sequence of Proteins. A messenger RNA molecule synthesized from the DNA directs the synthesis of the protein. Three adjacent nucleotides constitute a unit known as a codon; each codon codes for a single amino acid. There are 64 possible codons, 61 of which specify the 20 amino acids that make up proteins. Because most of the 20 amino acids are coded for by more than one codon, the code is called degenerate. Once thought to be identical in all forms of life, the genetic code has been found to vary slightly in certain organisms and in the mitochondria of some eukaryotes.
Genetic drift: Change in the pool of Genes of a small population that takes place strictly by chance. Genetic drift can result in genetic traits being lost from a population or becoming widespread in a population without respect to the survival or reproductive value of the gene pairs (alleles) involved. A random statistical effect, genetic drift can occur only in small, isolated populations in which the gene pool is small enough that chance events can change its makeup substantially. In larger populations, any specific allele is carried by so many individuals that it is almost certain to be transmitted by some of them unless it is biologically unfavourable.
Genetic engineering: Artificial manipulation, modification, and recombination of DNA or other nucleic-acid molecules in order to modify an organism or population of organisms. The term initially meant any of a wide range of techniques for modifying or manipulating organisms through heredity and reproduction. Now the term denotes the narrower field of recombinant-DNA technology, or gene cloning, in which DNA molecules from two or more sources are combined, either within cells or in test tubes, and then inserted into host organisms in which they are able to reproduce. This technique is used to produce new genetic combinations that are of value to science, medicine, agriculture, or industry. Through recombinant-DNA techniques, bacteria have been created that are capable of synthesizing human insulin, human interferon, human growth hormone, a hepatitis-B vaccine, and other medically useful substances. Recombinant-DNA techniques, combined with the development of a technique for producing antibodies in great quantity, have made an impact on medical diagnosis and cancer research. Plants have been genetically adjusted to perform nitrogen fixation and to produce their own pesticides. Bacteria capable of biodegrading oil have been produced for use in oil-spill cleanups. Genetic engineering also introduces the fear of adverse genetic manipulations and their consequences (e.g., antibiotic-resistant bacteria or new strains of disease). (See also Biotechnology).
Genetics: Study of heredity in general and of Genes in particular. Modern genetics began with the work of Gregor Mendel, who formulated the basic concepts of heredity. Walter S. Sutton proposed that Chromosomes were the site of Mendel’s hereditary factors. The Hardy-Weinberg Law established the mathematical basis for studying heredity in populations. Thomas Hunt Morgan provided evidence that genes occur on Chromosomes and that adjacent genes on the same chromosome form Linkage Groups. Oswald Avery showed that DNA is the chromosome component that carries genetic information. DNA’s molecular structure was deduced by James D. Watson and Francis Crick. These and other developments led to the deciphering of the Genetic Code of the DNA molecule, which in turn made possible the Recombination techniques of Genetic Engineering. An understanding of genetics is necessary for the diagnosis, prevention, and treatment of hereditary diseases, the breeding of plants and animals, and the development of industrial processes that use microorganisms.
Genotype: 1. Genetic makeup of an organism. The genotype determines the hereditary potentials and limitations of an individual. Among organisms that reproduce sexually, an individual’s genotype comprises the entire complex of genes inherited from both parents. Sexual reproduction guarantees that each individual has a unique genotype, except for identical twins, which come from the same fertilized egg. (See also Phenotype, Variation). 2. An individual hereditary constitution derived from its parents and forming a unique combination of genes; sometimes referring to trees having similar genetic constitutions with regard to certain common, identifiable, genetic characteristics, expressed in the phenotype.
Genus: 1. Biological classification. It ranks below family and above species, consisting of structurally or phylogenetically (see phylogenetic tree) related species or a single species exhibiting unusual differences. For example, the species of roses collectively form the genus Rosa and those of horses, donkeys, and zebras form the genus Equus. The genus name, capitalized and usually italicized, is the first word of a scientific name in the system of Binomial Nomenclature. 2. A botanical grouping of plants with similar characteristics. Species within a genus may be crossbred, but resulting offspring will usually be sterile. Genus Pinus contains ponderosa pine, lodge pole pine, and hundreds of other pines around the world. Each species within the genus is identified as Pinus + species name (in ponderosa’s case, Pinus ponderosa. Hence, each tree has both a genus name and a species name
Geochemistry: Scientific discipline dealing with the relative abundance, distribution, and migration of the Earth’s chemical elements and their isotopes. Historically, geochemistry was concerned primarily with defining elemental abundances in minerals and rocks. Modern geochemical research also includes study of the continual recycling of the Earth’s constituent materials through geologic processes, the cyclic flow of individual elements (and their compounds) between living and nonliving systems, and certain areas of Cosmology.
Geochronology: Dating and interpretation of geologic events in the history of the Earth. The classical technique of geochronology was Stratigraphy, including faunal succession. Since the mid 20th century, radiometric dating has provided absolute age data to supplement the relative dates obtained from the fossil record. Radiometric dating is based on the principle that radioactive isotopes in geologic material decay at constant, known rates to daughter isotopes. (See also Carbon-14 Dating).
Geographic information system (GIS): 1. An information system that uses a spatial database to provide answers to queries of a geographical nature through a variety of manipulations, such as sorting, selective retrieval, calculation, spatial analysis, and modeling. 2. Geographic Information System (GIS), computer system that records, stores, and analyzes information about the features that make up the earth’s surface. A GIS can generate two- or three-dimensional images of an area, showing such natural features as hills and rivers with artificial features such as roads and power lines. Scientists use GIS images as models, making precise measurements, gathering data, and testing ideas with the help of the computer.
Geography: Science of the Earth’s surface, which describes and analyzes the spatial variations in physical, biological, and human phenomena that occur on the surface of the globe and treats their interrelationships and their significant regional patterns. Once associated entirely with mapping and the exploration of the Earth, the field today is wide-ranging, and geographers use a variety of methods and techniques drawn from numerous disciplines. Subfields of geography include physical, human, and regional geography, which may range in scale from worldwide to a continent, a country, or a city.
Geologic time: Interval of time occupied by the Earth’s geologic history, extending from c. 3.9 billion years ago (corresponding to the age of the oldest known rocks) to the present day. It is, in effect, the part of the Earth’s history that is recorded in rock strata. The geologic time scale is classified in nested intervals distinguished by characteristic geologic and biologic features. From longest to shortest duration, the intervals are Eon, Era, Period, and Epoch. (See table below).
Geology: [Mid-18th century. < modern Latin geologia “description of the Earth”] Scientific study of the Earth, including its composition, structure, physical properties, and history. Geology is commonly divided into subdisciplines concerned with the chemical makeup of the Earth, including the study of minerals (mineralogy) and rocks (petrology); the structure of the Earth (structural geology) and volcanic phenomena (volcanology); landforms and the processes that produce them (geomorphology and glaciology); geologic history, including the study of fossils (paleontology), the development of sedimentary strata (stratigraphy), and the evolution of planetary bodies and their satellites (astrogeology); and economic geology and its various branches, such as mining geology and petroleum geology. Some major fields closely allied to geology are geodesy, geophysics, and geochemistry.
Geomagnetic field: Magnetic field associated with the Earth. It is essentially dipolar (i.e., it has two poles, the northern and southern magnetic poles) on the Earth’s surface. Away from the surface, the field becomes distorted. Most geo-magnetists explain the field by means of dynamo theories, whereby a source of energy in the Earth’s Core causes a self-sustaining magnetic field. In the dynamo theories, fluid motion in the Earth’s core involves the movement of conducting material within an existing magnetic field, thus creating a current and a self-enforcing field.
Geomagnetic reversal: Alternation of the Earth’s magnetic polarity. The Earth’s internal magnetic field reverses, on average, about every 300,000 to 1 million years. This reversal is very sudden on a geologic time scale, apparently taking about 5,000 years. The time between reversals is highly variable, sometimes less than 40,000 years and at other times as long as 35 million years. No regularities or periodicities have yet been discovered. A long interval of one polarity may be followed by a short interval of opposite polarity.
Geomagnetics: Branch of geophysics concerned with all aspects of the Earth’s magnetic field, including its origin, variation through time, and manifestations in the form of magnetic poles, the magnetization of rocks, and local or regional magnetic anomalies.
Geomorphology: Scientific discipline that describes and classifies the Earth’s topographic features. Many systems of classifying landforms have been devised. Some systems describe and group topographic features primarily according to the processes that shaped or modified them. Others take additional factors into consideration (e.g., character of the surface rocks and climatic variations) and include the developmental stage of landforms as an aspect of their evolution over geologic time.
Geophysics: Major branch of earth science that applies the principles and methods of physics to the study of the Earth. Geophysics deals with such geologic phenomena as the temperature distribution of the Earth’s interior; the source, configuration, and variations of the Geomagnetic Field; and the large-scale features of the terrestrial Crust, such as rifts, continental sutures, and oceanic ridges. Modern geophysical research also examines phenomena of the outer parts of the Earth’s atmosphere and even the physical properties of other planets and their satellites.
Geothermal energy: Power obtained by using heat from the Earth’s interior. Most geothermal resources are in regions of active Volcanism. Hot springs, geysers, pools of boiling mud, and fumaroles are the most easily exploited sources. The ancient Romans used hot springs to heat baths and homes, and similar uses are still found in Iceland, Turkey, and Japan. Geothermal energy’s greatest potential lies in the generation of electricity. It was first used to produce electric power in Italy in 1904. Today geothermal power plants are in operation in New Zealand, Japan, Iceland, Mexico, the U.S., and elsewhere.
German shepherd or Alsatian: Breed of Working Dog developed in Germany from traditional herding and farm dogs. A strongly built, long-bodied dog, it stands 23–25 in. (58–64 cm) high and weighs 75–95 lbs (34–43 kg). Its coat is of coarse, medium-long outer hair and shorter, dense inner hair and ranges from white or pale gray to black; often it is gray and black or black and tan. Noted for intelligence, alertness, and loyalty, it is used as a guide for the blind, as a watchdog, and in police and military work.
Germination test: A test made to determine the viability of seeds, spores, or pollen grains in a given sample.
Germinative capacity: The percentage of seeds, spores, or pollen grains in a given sample that actually germinate, irrespective of time. In any batch of seeds, the percentage that is pure (of the species required) multiplied by the germinative capacity gives the proportion of pure live seeds.
Germinative energy: The percentage of seeds, spores, or pollen grains in a given sample germinating within a given period e.g., 7 or 14 days, under optimum or stated conditions.
Gibraltar: British colony, on the Mediterranean coast of southern Spain. Area: 2.25 sq mi (5.8 sq km). Population (2005 est.): 27,884. It occupies a narrow peninsula 3 mi (5 km) long and 0.75 mi (1.2 km) wide that is known as the Rock. It appears from the east as a series of sheer, inaccessible cliffs, which makes it strategically important. It is the site of a British air and naval base that guards the Strait of Gibraltar. The Moors held Gibraltar from 711 to 1462, and in 1501 it was annexed by Spain. Captured by the British in 1704, it became a British crown colony in 1830. Gibraltar was an important port in World Wars I and II. The sovereignty of the territory has remained a source of constant friction between the United Kingdom and Spain, though residents voted in 1967 to remain part of Britain. Spain lifted its border blockade in the mid-1980s. Perhaps its most famous residents are the Barbary macaques, who occupy many of Gibraltar’s caves and are Europe’s only free-living monkeys.
Gill: [14th century. < Old Norse] the organ that fish and some other water animals use to breathe, consisting of a membrane containing many blood vessels through which oxygen passes. They are internal in most fish and external in tadpoles and some mollusks. (Pic at Fish)
Ginger: Herbaceous perennial plant (Zingiber offıcinale; family Zingiberaceae), probably native to South Asia, or its aromatic, pungent Rhizome, which is used as a spice, flavouring, food, and medicine. The spice has a slightly biting taste and is used, usually dried and ground, to flavour breads, sauces, curry dishes, confections, pickles, and ginger ale. The fresh rhizome is used in cooking. The leafy stems of the plant bear flowers in dense cone like spikes. Oil distilled from the rhizome is used in foods and perfumes
Ginkgo: Tree (Ginkgo biloba, family Ginkgoaceae) that is the only living representative of the gymnosperm order Ginkgoales. Native to China, it is often termed a living fossil because it is unclear whether uncultivated groups can be found in the wild. It has been planted since ancient times in Chinese and Japanese temple gardens and is now valued in many parts of the world as an attractive, fungus- and insect resistant ornamental tree. It tolerates cold weather and, unlike most gymnosperms, can survive the adverse atmospheric conditions of urban areas. Pyramidal in shape, it has a columnar, sparingly branched trunk. The light-coloured wood, soft and weak, has little economic value. The fan-shaped, leathery leaves, most divided into two lobes by a central notch, resemble the leaflets of the maidenhair fern. The silvery nut, when roasted, is considered a delicacy. Studies have suggested that Ginkgo biloba supplements can enhance memory function in the elderly and delay the onset of Alzheimer disease.
Girdle: To encircle the stem of a living tree with cuts that completely severs bark and cambium and often are carried well into the outer sapwood, done to kill the tree by preventing the passage of carbohydrates to the roots. Also refers to same process caused by animals, such as mice or beaver
Girdling: 1. Silviculture: Making more or less continuous incisions around a living stem, through at least both bark and cambium, generally with the object of killing the tree. Sometimes termed mechanical girdling, to distinguish it from herbicide girdling when herbicide is added. Making a series of close downward and upward, i.e., V-shaped, incisions into the sapwood is termed notch-girdling. 2. Forest protection: Destruction (on the part of agencies other than human, e.g., insects, rodents) of tissue, particularly living tissue, in a rough ring around a stem, branch, or root.
cf. frill girdling, bark stripping
Giraffe: species of Ruminant (Giraffa camelopardalis) that is the tallest of all mammals. It reaches an overall height of 18 ft (5.5 m) or more. The legs and neck are extremely long. The giraffe has a short body, a tufted tail, a short mane, and short, skin covered horns. The back slopes downward to the hindquarters. The coat is pale buff, with reddish brown spots. It feeds primarily on Acacia leaves. It lives in herds on savannas and in open bush country and is native to most of sub-Saharan Africa. Giraffes are still numerous in eastern Africa, where they are protected, but hunting has reduced their populations elsewhere. The only other member of the family Giraffidae is the Okapi.
Girder: In building construction, a large main supporting beam, commonly of steel or Reinforced Concrete, that carries a heavy transverse (crosswise) load. In a floor system, beams and joists transfer their loads to the girders, which in turn frame into the columns.
Girth: (Syn Circumference) The length around the outside of the bole. Circumference is commonly measured in forestry, but usually it is then used to estimate bole diameter. If the bole were circular, diameter can be estimated as circumference divided by PI (3.14…). However, if the bole deviates from this ideal shape, then this calculation will overestimate the diameter. This bias is not constant and will vary with the degree and type of deviation. However, this bias is rarely considered significant. (Pics)
Glabrous: Not hairy.
Glacier: Large mass of perennial ice that forms on land through the recrystallization of snow and that moves forward under its own weight. The term ice sheet is commonly applied to a glacier that occupies an extensive tract of relatively level land and that flows from the centre outward. Glaciers occur where snowfall in winter exceeds melting in summer, conditions that prevail only in high mountain areas and Polar Regions. Glaciers occupy about 11% of the Earth’s land surface but hold roughly three-fourths of its fresh water; 99% of glacier ice lies in Antarctica and Greenland.
Glaciology: Scientific discipline concerned with all aspects of ice on landmasses. It deals with the structure and properties of Glacier ice, its formation and distribution, the dynamics of ice flow, and the interactions of ice accumulations with climate. Glaciological research is conducted in a variety of ways, including radar sounding, boreholes, lateral tunnels, and remote sensing with satellite-borne infrared and multispectral scanners.
Glandular: Having glands, which secrete sticky substances.
Glass: Solid material, typically a mix of inorganic compounds, usually transparent or translucent, hard, brittle, and impervious to the natural elements (“vitreous properties”). It is made by cooling molten ingredients fast enough so no visible crystals form. A poor conductor of heat and electricity, glass takes on colours when certain metal Oxides are included in the mix. Most glass breaks easily. Obsidian is a naturally occurring glass. Everyday glass (soda-lime or soda-lime-silica) is made of silica (silicon dioxide), soda (sodium carbonate), and limestone (calcium carbonate), with magnesia (magnesium oxide) for sheet glass or alumina (aluminum oxide) for bottle glass. Fused silica is an excellent glass but expensive because of pure silica’s very high melting point. Borosilicate glass (e.g., Pyrex) is used for cookware and laboratory glassware because it expands very little when heated. Lead crystal is used for fine tableware. It has a heavy feel because of its lead oxide content and a sparkle due to its high refraction index. Even more specialized glasses include optical, photosensitive, metallic, and fibre-optic. Since glass has no sharp melting point, most types can be shaped while hot and plastic by many techniques, mostly blowing or molding. (See also Volcanic Glass).
Glaucous: Covered with bloom.
Gley: Sticky clay soil or soil layer formed under the surface of some waterlogged soils. Characteristic of poorly drained areas, gley soils contain reduced amounts of iron and other elements and are gray and mottled in colour.
Global Positioning System (GPS): Precise satellite-based navigation and location system originally developed for U.S. military use. GPS is a fleet of more than 24 communications satellites that transmit signals globally around the clock. With a GPS receiver, one can quickly and accurately determine the latitude, the longitude, and in most cases the altitude of a point on or above Earth’s surface. A single GPS receiver can find its own position in seconds from GPS satellite signals to an accuracy of one metre; accuracy within one centimeter can be achieved with sophisticated military-specification receivers. This capability has reduced the cost of acquiring spatial data for making maps while increasing cartographic accuracy. Other applications include measuring the movement of polar ice sheets or even finding the best automobile route between given points.
Global Warming /Climate Change: Increase in the global average surface temperature resulting from enhancement of the Greenhouse Effect, primarily by Air Pollution. In 2001 the UN Intergovernmental Panel on Climate Change estimated that by 2100 global average surface temperatures would increase 2.5 to 10.4 °F (1.4 to 5.8 °C), depending on a range of scenarios for greenhouse gas emissions. Many scientists predict that such an increase would cause polar ice caps and mountain glaciers to melt rapidly, significantly raising the levels of coastal waters, and would produce new patterns and extremes of drought and rainfall, seriously disrupting food production in certain regions. Other scientists maintain that such predictions are overstated. The 1992 Earth Summit and the 1997 Kyoto Protocol to the United Nations Framework Convention on Climate Change attempted to address the issue of global warming, but in both cases the efforts were hindered by conflicting national economic agendas and disputes between developed and developing nations over the cost and consequences of reducing emissions of greenhouse gases.
Globalization: Process by which the experience of everyday life, marked by the diffusion of commodities and ideas, is becoming standardized around the world. Factors that have contributed to globalization include increasingly sophisticated communications and transportation technologies and services, mass migration and the movement of peoples, a level of economic activity that has outgrown national markets through industrial combinations and commercial groupings that cross national frontiers, and international agreements that reduce the cost of doing business in foreign countries. Globalization offers huge potential profits to companies and nations but has been complicated by widely differing expectations, standards of living, cultures and values, and legal systems as well as unexpected global cause-and-effect linkages.
Globose: Approximately spherical.
Glowworm: Any crawling, luminous insect that emits light either continuously or in prolonged glows rather than in the brief flashes characteristic of most Fireflies. Glowworms include larvae and adult (often wingless) females of fireflies and certain other Beetle species and larvae of certain Gnat species. They are widely distributed. The great diversity in the size, number, location, and structure of the bioluminescent organs suggests that the light producing ability of the various species evolved independently.
Glucose or dextrose or grape sugar or corn sugar: Organic compound, a simple sugar (monosaccharide), chemical formula C6H12O6. The product of photosynthesis in plants, it is found in fruits and honey. As the major circulating free sugar in blood, it is the source of energy in cell function and a major participant in metabolism. Control of its level and metabolism is of great importance. Glucose and fructose make up sucrose. Glucose units in long chains make up polysaccharides (e.g., cellulose, glycogen, starch). Glucose is used in foods, medicine, brewing, and wine making and as the source of various other organic chemicals.
Glue: Adhesive substance resembling gelatin, extracted from animal tissue, particularly hides and bones, or from fish, casein (milk protein), or vegetables. Glue was used as early as 3000 BC in wooden-furniture construction in Egypt. Synthetic Resin adhesives such as the Epoxies are replacing glue for many uses, but glue is still widely used as an adhesive in wood working and in certain manufacturing and other industrial processes.
Gneiss: Medium- to coarse-grained metamorphic rock with parallel, somewhat irregular banding that has little tendency to split along planes. Gneiss is the principal rock over extensive metamorphic terrains. Orthogneiss is formed by the metamorphism of igneous rocks; paragneiss results from the metamorphism of original sedimentary rocks. Pencil gneiss contains rod-shaped individual minerals or segregations of minerals, and augen gneiss contains large lenticular mineral grains or mineral aggregates having the appearance of eyes scattered through the rock.
Goat: Any hollow-horned Ruminant in the Bovid genus Capra. Goats have a lighter build and straighter hair than Sheep; their horns arch backward; and the tail is short. Males usually have a beard. Wild goats include the Ibex and markhor. Domesticated goats are descended from the pasang, which is probably native to Asia. In China, Great Britain, Europe, and North America, the domestic goat is primarily a milk producer; much of the milk is used to make cheese. Some breeds, notably the angora and cashmere, are raised for their wool; young goats are the source of kid leather.
Gobi Desert: Desert, Central Asia. One of the great desert and semi-desert regions of the world, the Gobi stretches across Central Asia over large areas of Mongolia and China. It occupies an arc of land 1,000 mi (1,609 km) long and 300–600 mi (500–1,000 km) wide, with an estimated area of 500,000 sq mi (1,300,000 sq km). Contrary to the image often associated with a desert, much of the Gobi is not sandy but covered with bare rock.
Golden eagle: Dark-brown EAGLE (Aquila chrysaetos) with golden, leaf-shaped nape feathers, dark eyes, gray beak, fully feathered legs, large yellow feet, and large talons. Its wingspread reaches almost 8 ft (2.3 m). It ranges from central Mexico (where it is the national bird) along the Pacific coast and through the Rocky Mountains to Alaska, and small numbers are found from Newfoundland to North Carolina. Also found in North Africa, it is more common across Russia, to southern China and Japan. It nests in cliff caves or in lone trees. The species is protected in the U.S.
Golden Gate Bridge: Suspension bridge spanning the Golden Gate, San Francisco. From its completion in 1937 until the completion of New York’s Verrazano- Narrows Bridge in 1964, it had the longest main span in the world, 4,200 ft (1,280 m). It remains incomparable in its magnificence. Its construction, supervised by Joseph B. Strauss (1870–1938), involved many difficulties: rapidly running tides, frequent storms and fogs, and the problem of
blasting rock under deep water to plant earthquake-resistant foundations.
Goldfish: Ornamental aquarium and pond fish (Carassius auratus) of the CARP family, native to East Asia but introduced into many other areas. The goldfish was domesticated by the Chinese at least as early as the Song dynasty (960–1279). It is naturally greenish brown or gray, but its colour varies. Selective breeding has produced more than 125 breeds, including the veiltail, with a three-lobed, flowing tail, and the common, pet-shop comet. They feed on plants and small animals and, in captivity, on small crustaceans and other foods. They have become naturalized in many parts of the eastern U.S.
Gold standard: Monetary system in which the standard unit of Currency is a fixed quantity of Gold or is freely convertible into gold at a fixed price. The gold standard was first adopted in Britain in 1821. Germany, France, and the U.S. instituted it in the 1870s, prompted by North American gold strikes that increased the supply of gold. The gold standard ended with the outbreak of World War I in 1914; it was reestablished in 1928, but because of the relative scarcity of gold, most nations adopted a gold-exchange standard, supplementing their gold reserves with currencies (U.S. dollars and British pounds) convertible into gold at a stable rate of exchange. Though the gold-exchange standard collapsed during the Great Depression, the U.S. set a minimum dollar price for gold, an action that allowed for the restoration of an international gold standard after World War II. In 1971 dwindling gold reserves and an unfavourable Balance of Payments led the U.S. to suspend the free convertibility of dollars into gold, and the gold standard was abandoned.
Goose: Any of various large, heavy-bodied waterfowl (family Anatidae), especially those of the genera Anser (so-called gray geese) and Branta (so-called black geese), which are found only in the Northern Hemisphere. Intermediate in size and build between Ducks and Swans, geese are less fully aquatic than either, and their legs are farther forward, allowing them to walk readily. Geese have a specially modified bill for grasping sedges and grasses, their main diet. The sexes are alike in coloration; males (called ganders) are usually larger than females. Both sexes utter loud honking or gabbling cries while in flight or when danger appears. Geese pair for life. Flocks traveling in V-formations migrate between their northern breeding grounds and southern wintering grounds
Gorilla: Largest of the great Apes. A stocky, powerful forest dweller native to equatorial Africa, the gorilla (Gorilla gorilla) has black skin and hair, large nostrils, and prominent brow ridges. Adults have long, powerful arms; short, stocky legs; an extremely thick, strong chest; and a protruding abdomen. Adult males have a prominent crest on top of the skull and a “saddle” of gray or silver hairs on the lower part of the back. Males, about twice as heavy as females, may reach a height of about 5.5 ft (1.7 m) and a weight of 300– 600 lbs (135–275 kg). Gorillas are mainly terrestrial, walking about on all four limbs. They live in stable family groups of six to 20 animals that are led by one or two silver backed males. They eat leaves, stalks, and shoots. They are unaggressive and even shy unless provoked. They are calmer and more persistent than chimpanzees; though not as adaptable; gorillas are highly intelligent and capable of problem solving. The gorilla is hunted for its body parts and meat, and its habitat is disappearing. It is an Endangered Species throughout its range; the mountain subspecies is critically endangered.
Gout: Formation of swellings at nodes or at the base of buds.
Government: Political system by which a body of people is administered and regulated. Different levels of government typically have different responsibilities. The level closest to those governed is local government. Regional governments comprise a grouping of individual communities. National governments nominally control all the territory within internationally recognized borders and have responsibilities not shared by their subnational counterparts. Most governments exercise Executive, legislative, and judicial powers and split or combine them in various ways. Some also control the religious affairs of their people; others avoid any involvement with religion. Political forms at the national level determine the powers exercised at the subnational levels; these have included autocracy, Democracy, Fascism, Monarchy, Oligarchy, plutocracy (government by the wealthy), Theocracy, and Totalitarianism
Grade: 1. A system of classifying lumber or logs according to quality. 2. The steepness of a forest road.
Graft: In horticulture, the act of placing a portion of one plant (called a bud or scion) into or on a stem, root, or branch of another (called the stock) in such a way that a union forms and the partners continue to grow. Grafting is used for various purposes: to repair injured trees, produce dwarf trees and shrubs, strengthen plants’ resistance to certain diseases, retain varietal characteristics, adapt varieties to adverse soil or climatic conditions, ensure pollination, produce multifruited or multiflowered plants, and propagate certain species (such as hybrid roses) that can be propagated in no other way. In theory, any two plants that are closely related botanically and that have a continuous CAMBIUM can be grafted. Grafts between species of the same genus are often successful and between genera occasionally so, but grafts between families are nearly always failures. (See illustration).
Grain: 1. The direction, size, arrangement, appearance, or quality of the fibers in wood. 2. Achene-like fruit, but with the seed not loose.
Gram: Unit of mass or weight used especially in the centimeter-gram-second (CGS) system of measurement. One gram is equal to 0.001 kg, about 0.035 oz, or 15.43 grains. The gram is very nearly equal to the mass of 1 cc of pure water at its maximum density. The gram of force is equal to the weight of a gram of mass under standard gravity. For greater precision, the mass may be weighed at a point at which the acceleration due to gravity is 980.655 cm/sec2.
Granite: Coarse- or medium-grained intrusive rock that is rich in quartz and Alkali Feldspar. One of the most common rocks of the Earth’s crust, it is formed by the cooling of Magma. Granite was once used extensively as paving blocks and building stone, but today its principal uses are as roadway curbing, veneer for building faces, and tombstones. Granite characteristically forms irregular masses of extremely variable size, ranging from less than 5 mi (8 km) in maximum dimension to larger masses (Batholiths) that are often hundreds of square miles in area.
Granular application: A general process by which fertilizers or herbicides in the form of grains are applied to a given area.
Grape: Any of the 60 plant species that make up the genus Vitis (family Vitaceae), native to the northern temperate zone, including varieties that may be eaten as table fruit, dried to produce raisins, or crushed to make grape juice or wine. V. vinifera is the species most commonly used in wine making. The grape is usually a woody vine, climbing by means of tendrils. In arid regions it may form an almost erect shrub. Botanically, the fruit is a berry. Grapes contain such minerals as calcium and phosphorus and are a source of vitamin A. All grapes contain sugar (glucose and fructose) in varying quantities depending on the variety.
Grapefruit: Tree (Citrus paradisi) of the Rue Family and its edible fruit. It originated in the West Indies (probably Jamaica) before being brought to the New World mainland. The shiny, dark green foliage is very dense. The large white flowers are borne singly or in clusters. Lemon yellow when ripe, the fruit is 4–6 in. (100–150 mm) in diameter, about twice as large as a medium-size orange. The mildly acidic pulp—juicy and light yellowish, pink, or red—is an excellent source of vitamin C. It is popular as breakfast fruit in various parts of the world.
Graph: Visual representation of a data set or a mathematical equation, inequality, or function to show relationships or tendencies that these formulas can only suggest symbolically and abstractly. Though histograms and pie charts are also graphs, the term usually applies to point plots on a coordinate system. For example, a graph of the relationship between real numbers and their squares matches each real number on a horizontal axis with its square on a vertical axis. The resulting set of points in this case is a parabola. A graph of an inequality is usually a shaded region on one side of a curve, whose shape depends not only on the equation or inequality but on the coordinate system chosen.
Grass: Any of many low, green, non-woody plants that make up the families Poaceae (or Gramineae), Cyperaceae (Sedges), and Juncaceae (Rushes). Only the approximately 8,000–10,000 species in the family Poaceae are true grasses. They are the most economically important of all Flowering plants because of their nutritious grains and soil-forming function, and they are the most widespread and most numerous of plants. The cereal grasses include wheat, corn, rice, rye, oats, barley, and millet. Grasses provide forage for grazing animals, shelter for wildlife, and construction materials, furniture, utensils, and food for humans. Some species are grown as garden ornamentals, cultivated as Turf for lawns and recreational areas, or used as cover plants for erosion control. Most have hollow, segmented, round stems, bladelike leaves, and extensively branching fibrous root systems.
Grass leaves: Grass leaves have a considerably different morphology than do leaves of most all other plants. Grass leaves are composed of a sheath, blade, auricle and ligule. The sheath is the blade-like portion that acts like the petiole of the leaf, only it is flat and blade-like and surrounds the stem, connecting to the node below. The blade extends at a right angle to the sheath. The ligule is a small tongue-like flat of tissue that extends out from the sheath and parallel to it above the blade and perpendicular to the blade. The auricles are two small flaps of tissue that extend out from the blade and perpendicular to the sheath, partially surrounding the stem. (See illustration) (Pic at Blade)
Grasshopper: Any of the leaping insects of the family Acrididae (shorthorned grasshoppers) or Tettigoniidae (long-horned grasshoppers), both in the order Orthoptera. Grasshoppers are most common in tropical forests, semiarid regions, and grasslands. Colours range from green to olive or brown, sometimes with yellow or red markings. Grasshoppers eat plant material and may damage crops. Some species are more than 4 in. (11 cm) long. The male can produce a buzzing sound either by rubbing its front wings together or by rubbing tooth like ridges on the hind legs against a raised vein on each front wing. Grasshoppers are a favourite food of many birds, frogs, and snakes.
Gravel: [13th century French grave “pebbles”] Aggregate of more or less rounded rock fragments coarser than sand (i.e., more than 0.08 in., or 2 mm, in diameter). Gravel beds in some places contain heavy metallic ore minerals, such as cassiterite (a major source of tin), or native metals, such as gold, in nuggets or flakes. Deposits accumulate in parts of stream channels or on beaches where the water moves too rapidly to permit sand to remain. Because of changing conditions, gravel formations generally are more limited and more variable in coarseness, thickness, and configuration than sand or clay deposits. In many regions gravel terraces (or raised beaches) extend great distances inland, indicating that the sea at one time stood higher than it does today. Gravels are widely used building materials.
Gravel road: It is composed of weak concrete in which silt clay and sand form the mortar and stones form the coarse aggregate. (Compare Metallic road)
Gravitation: Universal force of attraction that acts between all bodies that has Mass. Though it is the weakest of the four known forces, it shapes the structure and evolution of stars, galaxies, and the entire universe. The laws of gravity describe the trajectories of bodies in the solar system and the Motion of objects on Earth, where all bodies experience a downward gravitational force exerted by Earth’s mass, the force experienced as weight. Isaac Newton was the first to develop a quantitative theory of gravitation, holding that the force of attraction between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. Albert Einstein proposed a whole new concept of gravitation, involving the four-dimensional continuum of Space-Time which is curved by the presence of matter. In his general theory of Relativity, he showed that a body undergoing uniform acceleration is indistinguishable from one that is stationary in a gravitational field.
Gravity, centre of: Imaginary point where the total weight of a material body may be thought to be concentrated. Since weight and Mass are proportional, the same point may also be called the centre of mass, but the centre of mass does not require a gravitational field. A body’s centre of gravity may coincide with its geometric centre, especially if the body is symmetric and composed of homogeneous material. In asymmetric, unhomogeneous, or hollow objects, the centre of gravity may be at some distance from the geometric centre or even at a point in space external to the object, such as between the legs of a chair.
Grazing: grass and green plants for animals such as cows and sheep to eat; the eating of any kind of standing vegetation by domestic livestock or wild animals (SAF) Sometimes limited to eating of herbage in contrast with browsing (See also: Conservative grazing, Rotational grazing, Seasonal grazing, Selective grazing)
Grazing capacity: In range management, the ability of a range unit, in years of normal rainfall, to give adequate support to a constant number of livestock for a stated period each year without deteriorating. Expressed in number of livestock per acre of given kind or kinds, or in number of acres per specified animals.
Great Barrier Reef: Extensive complex of Coral Reefs, shoals, and islets in the Pacific Ocean, off the northeastern coast of Australia. The largest deposit of Coral in the world, it extends for more than 1,250 mi (2,000 km) along the coast of Queensland and has an area of some 135,000 sq mi (350,000 sq km). The reef has been formed over millions of years from the skeletons of a mass of living marine organisms. In addition to at least 300 species of hard coral, marine life includes anemones, worms, gastropods, lobsters, crayfish, prawns, crabs, and a variety of fishes. Encrusting red Algae form the purplish red algal rim that is one of the reef’s characteristic features. A major tourist attraction, nearly all of it is within Great Barrier Reef National Park; the reef was designated a UNESCO World Heritage Site in 1981.
Greater earthquake: An earthquake having a magnitude of 8 or greater on the Richter scale.
Great Lakes: Chain of lakes, east-central North America. Comprising Lakes Superior, Michigan, Huron, Erie, and Ontario, it forms a natural boundary between the U.S. and Canada. The Great Lakes cover an area of about 94,850 sq mi (245,660 sq km) and constitute the largest freshwater surface in the world. Connected to form a single waterway that discharges down the St. Lawrence River into the Atlantic Ocean, with the St. Lawrence Seaway they form a shipping lane more than 2,000 mi (3,200 km) long that carries oceangoing traffic as far west as Duluth, Minn. Large quantities of iron ore, coal, grain, and manufactured goods are moved between lake ports and shipped overseas. While commercial fishing was once a major industry on the lakes, pollution and other factors led to its collapse; recovery has been slow and partial. The lakes are used for many recreational activities, including boating and sailing.
Great Wall of China Chinese Wanli Changcheng: Defensive wall, northern China. One of the largest building-construction projects ever carried out, it runs (with all its branches) about 4,500 mi (7,300 km) east to west from the Bo Hai (Gulf of Chihli) to a point deep in Central Asia. Large parts of the fortification date from the 7th to the 4th century BC. In the 3rd century BC the emperor Shihuangdi connected existing defensive walls into a single system fortified by watchtowers. These served both to guard the rampart and to communicate with the capital, Xianyang (near modern XI’AN) by signal—smoke by day and fire by night. Originally constructed partly of masonry and earth, it was faced with brick in its eastern portion. It was rebuilt in later times, especially in the 15th and 16th centuries. The basic wall is about 23–26 ft (7–8 m) high; at intervals towers rise above it to varying heights. It was designated a UNESCO World Heritage Site in 1987.
Great white shark or white shark: Large, aggressive Shark (Carcharodon carcharias, family Lamnidae), considered the species most dangerous to humans. It is found in tropical and temperate regions of all oceans and is noted for its voracious appetite. Its diet includes fishes, sea turtles, birds, sea lions, small whales, carcasses, and ships’ garbage. The great white is heavy-bodied and has a crescent-shaped tail and large, saw edged, triangular teeth. It can reach a length of more than 20 ft (6 m) and is generally gray, bluish, or brownish, with the colour shading suddenly into a whitish belly. Though it is widely feared, only a few hundred humans are known to have ever been killed by the great white shark.
Greenhouse: Building designed for the protection of tender or out-of season plants against excessive cold or heat. Usually a glass- or plastic enclosed structure with a framing of aluminum, galvanized steel, or such woods as redwood, cedar, or cypress, it is used for the production of fruits, vegetables, flowers, and any other plants requiring special temperature conditions. It is heated partly by the sun and partly by artificial means. This controlled environment can be adapted to the needs of particular plants.
Greenhouse effect: Warming of the Earth’s surface and lower atmosphere caused by water vapour, carbon dioxide, and other trace gases in the atmosphere. Visible light from the Sun heats the Earth’s surface. Part of this energy is radiated back into the atmosphere in the form of Infrared Radiation, much of which is absorbed by molecules of carbon dioxide and water vapour in the atmosphere and reradiated toward the surface as more heat. (Despite the name, the greenhouse effect is different from the warming in a greenhouse, where panes of glass allow the passage of visible light but hold heat inside the building by trapping warmed air.) The absorption of infrared radiation causes the Earth’s surface and lower atmosphere to warm more than they otherwise would, making the Earth’s surface habitable. An increase in atmospheric carbon dioxide caused by widespread combustion of Fossil Fuels may intensify the greenhouse effect and cause long-term climatic changes. Likewise, an increase in atmospheric concentrations of other trace greenhouse gases such as Chlorofluorocarbons, Nitrous Oxide, and Methane resulting from human activities may also intensify the greenhouse effect. From the beginning of the Industrial Revolution through the end of the 20th century, the amount of carbon dioxide in the atmosphere increased 30% and the amount of methane more than doubled. It is also estimated that the U.S. is responsible for about one-fifth of all human-produced greenhouse-gas emissions. (See also Global Warming).
Green lumber: 1. Lumber with the moisture content greater than that of air-dried lumber. 2. Unseasoned lumber, boards from logs processed through mill before drying.
Green manuring: 1. Crop grown and plowed under for its beneficial effects to the soil and subsequent crops, though during its growth it may be grazed. These crops are usually Annuals, either Grasses or Legumes. They add nitrogen to the soil, increase the general fertility level, reduce Erosion, improve the physical condition of the soil, and reduce nutrient loss from leaching. They are usually planted in the fall and turned under in the spring before the summer crop is sown. (See also Cover Crop). 2. Increasing the fertility of soil by raising suitable herbaceous crops on it, particularly Fabaceae, but also Cruciferae and Gramineae, and digging or ploughing them while succulent, with or without supplementary fertilizers.
Green Tree Reservoir (GTR): A wooded area that has been intentionally flooded to benefit migratory ducks and waterfowl. GTRs may be planted with a grain crop, such as millet, the summer before the winter flooding. The GTR can be an effective, low-cost method of luring waterfowl into forested tracts.
Greenwich: Outer borough (pop., 2001: 214,403), Greater London, on the southern bank of the River Thames. The meridian that passes through the borough serves as the basis for standard time as well as for reckonings of longitude throughout the world. Greenwich Park was enclosed by the duke of Gloucester in 1433; it was the site of the Royal Observatory (founded 1675). Other historic buildings include the Queen’s House, now part of the National Maritime Museum, and the Royal Naval College (1873–1998). These and other historic places were designated a UNESCO World Heritage Site in 1997. The Millennium Dome, constructed in the 1990s, was used for millennial celebrations to usher in the year 2000.
Greenwich Mean Time (GMT): Former name for mean solar time of the longitude (0°) of the former Royal Observatory at Greenwich, England, or Greenwich meridian. GMT was used to avoid potentially confusing references to local time systems (zones). In accord with tradition, 0000 GMT (denoting the start of a solar day) occurred at noon. In 1925 the numbering system for GMT was changed so that the day (like the civil day) began at midnight. Some confusion resulted, and in 1928 the International Astronomical Union changed the designation of the standard time of the zero meridians to Universal Time, which remains in general use. The term GMT is still used for some purposes (including navigation) in English-speaking countries.
Gregarious: Living in groups or communities.
Greyhound or grayhound: Fastest dog, one of the oldest breeds (dating from about 3000 BC in Egypt), and long symbolic of the aristocracy. It has a narrow head; long neck; deep chest; long, muscular hindquarters; a long, slim tail; and a short, smooth coat, of various colors. It stands 25–27 in. (64–69 cm) high and weighs 60–70 lbs (27–32 kg). Streamlined and slender, it can reach a speed of about 45 mph (72 kph). Greyhounds hunt by sight and may be used to hunt hares, deer, foxes, and small game. They are frequently raced for sport.
Grillage: Framework of beams: a framework of beams and crossbeams built as a foundation for a building on soft ground.
Grizzly bear: Large North American Brown Bear whose forms, including the Alaskan brown BEARS, are usually considered races or subspecies of a single species (Ursus arctos). The more than 80 forms once ranged over open regions of western North America from Mexico to Alaska, but their numbers have dwindled. Grizzlies have humped shoulders, an elevated forehead, and brownish to buff fur. They may grow to about 8 ft (2.5 m) long and weigh 900 lbs (410 kg). One variety, the Kodiak bear, is the largest living land carnivore, reaching lengths of more than 10 ft (3 m) and a weight of 1,700 lbs (750 kg). Grizzlies feed on game, fish, berries, and occasionally grass. They have been known to attack humans and are prized as big game.
Gross domestic product (GDP): Total market value of the goods and services produced by a nation’s economy during a specific period of time. GDP is customarily reported on an annual basis. It is defined to include all final goods and services—that is, those that are produced by the economic resources located in that nation regardless of their ownership and are not resold in any form. GDP differs from gross national product (GNP), which is defined to include all final goods and services produced by resources owned by that nation’s residents, whether located in the nation or elsewhere.
Group method: A shelterwood system in which the canopy is opened, by group cutting, so as to create fairly evenly distributed gaps which are enlarged by subsequent cuttings. Regeneration within gaps is mainly natural, though often supplemented artificially; regeneration interval is fairly short and resultant crop is more or less even-aged and regular.
Group planting: Setting out young trees in groups.
Group Selection: (a) The removal of small groups of trees to regenerate shade-intolerant trees in the opening (usually at least 1/4 acre). (b) A specific type of selective cutting.
Group-selection method: A method of regenerating and maintaining uneven-aged stands in which trees are removed in small groups.
Growing stock: The sum (by number or volume) of all the trees growing in the forest of a specified part of it. (SAF)
Growth promoter: Any agent present or provided as a supplement to the plant or its environment to activate growth.
Growth rate: With reference to wood, the rate at which wood has been added to the tree at any particular point, usually expressed in the number of annual rings per inch. May also be stated as “annual leader growth.”
Growth rings: The layers of wood a tree adds each season; also called annual rings. These rings frequently are visible when a tree is cut and can be used to estimate its age and growth rate.
Grub: An insect larva; a term loosely applied, usually to larvae of Coleoptera; larva is thick-bodied with well-developed thoracic legs but no abdominal prolegs.
Gryllidae (Crickets): Common name for insects of a family characterized by the chirping courtship call of the male and by the needlelike or cylindrical ovipositor (organ at the end of the abdomen where eggs are deposited) of the female.
Guard cells: The guard cells are are two crescent-shaped cells on either side of the pore of a stoma in the epidermis of the stem or leaf. By changing shape, the guard cells are able to cover and uncover the pore of the stoma and let oxygen out and carbon dioxide into the stem or leaf. Changes in turgor pressure is the mechanism by which the shape of the guard cell is altered so as to cover and uncover the pore.
Gyppo logger: A self-employed, independent timber harvesting contractor who is not an employee of the log purchaser. A more descriptive term is “contract logger.”
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Naeem Javid Muhammad Hassani