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  • Physics - 5 | Britannica.com
    British physicist whose discovery of the Josephson effect while a 22 year old graduate student won him a share with Leo Esaki and Ivar Giaever of the 1973 Nobel Prize for Physics At Trinity College Cambridge Josephson studied mathematics before Joule James Prescott English physicist who established that the various forms of energy mechanical electrical and heat are basically the same and can be changed one into another Thus he formed the basis of the law of conservation of energy the first law of thermodynamics Kamerlingh Onnes Heike Dutch winner of the Nobel Prize for Physics in 1913 for his work on low temperature physics and his production of liquid helium He discovered superconductivity the almost total lack of electrical resistance in certain materials when cooled to a temperature Kao Charles physicist who was awarded the Nobel Prize for Physics in 2009 for his discovery of how light can be transmitted through fibre optic cables He shared the prize with physicists Willard Boyle and George E Smith who won for their work in inventing the Kapitsa Pyotr Leonidovich Soviet physicist who invented new machines for liquefaction of gases and in 1937 discovered the superfluidity of liquid helium He was a corecipient of the 1978 Nobel Prize for Physics for his basic inventions and discoveries in the area of low temperature Kastler Alfred French physicist who won the Nobel Prize for Physics in 1966 for his discovery and development of methods for observing Hertzian resonances within atoms In 1920 Kastler went to Paris to study at the École Normale Supérieure After serving on the science Katz Sir Bernard German born British physiologist who investigated the functioning of nerves and muscles His studies on the release of the neurotransmitter acetylcholine which carries impulses from nerve fibre to muscle fibre or from one nerve ending to another won Katzir Ephraim Russian born scientist and politician who was the fourth president of Israel 1973 78 Katzir moved with his family to Palestine when he was nine years old After graduating from the Hebrew University of Jerusalem he became an assistant in the university s Kayser Heinrich Gustav Johannes German physicist who discovered the presence of helium in the Earth s atmosphere Kayser s early research work was on the properties of sound In collaboration with the physicist and mathematician Carl D T Runge Kayser carefully mapped the spectra Keesom Willem Hendrik Dutch physicist who specialized in cryogenics and was the first to solidify helium Having taken his doctorate from the University of Amsterdam in 1904 Keesom worked under Heike Kamerlingh Onnes at the University of Leiden and then in 1917 joined the Kelvin William Thomson Baron Scottish engineer mathematician and physicist who profoundly influenced the scientific thought of his generation Thomson who was knighted and raised to the peerage in recognition of his work in engineering and physics was foremost among the small Kendall Henry Way American nuclear physicist who shared the 1990 Nobel Prize for Physics with Jerome Isaac Friedman and Richard E Taylor for obtaining experimental evidence for the existence of the subatomic particles known as quarks Kendall received his B A from Amherst Kepler Johannes German astronomer who discovered three major laws of planetary motion conventionally designated as follows 1 the planets move in elliptical orbits with the Sun at one focus 2 the time necessary to traverse any arc of a planetary orbit is proportional Kerr Roy P New Zealand mathematician who solved 1963 Einstein s field equations of general relativity to describe rotating black holes thus providing a major contribution to the field of astrophysics Kerr received an M S 1954 from New Zealand University Ketterle Wolfgang German born physicist who with Eric A Cornell and Carl E Wieman won the Nobel Prize for Physics in 2001 for creating a new ultracold state of matter the so called Bose Einstein condensate BEC In 1986 Ketterle received a Ph D from the University Khariton Yuly Borisovich founder and head from 1946 to 1992 of the research and design laboratory known variously as KB 11 Arzamas 16 and currently the All Russian Scientific Research Institute of Experimental Physics which was responsible for designing the first Soviet Kilby Jack American engineer and one of the inventors of the integrated circuit a system of interconnected transistors on a single microchip In 2000 Kilby was a corecipient with Herbert Kroemer and Zhores Alferov of the Nobel Prize for Physics Education and kinematics branch of physics and a subdivision of classical mechanics concerned with the geometrically possible motion of a body or system of bodies without consideration of the forces involved i e causes and effects of the motions A brief treatment of kinematics kinetics branch of classical mechanics that concerns the effect of forces and torques on the motion of bodies having mass Authors using the term kinetics apply the nearly synonymous name dynamics to the classical mechanics of moving bodies This is in contrast Kirchhoff Gustav Robert German physicist who with the chemist Robert Bunsen firmly established the theory of spectrum analysis a technique for chemical analysis by analyzing the light emitted by a heated material which Kirchhoff applied to determine the composition of Klitzing Klaus von German physicist who was awarded the Nobel Prize for Physics in 1985 for his discovery that under appropriate conditions the resistance offered by an electrical conductor is quantized that is it varies by discrete steps rather than smoothly and continuously Kobayashi Makoto Japanese scientist who was a corecipient with Yoichiro Nambu and Maskawa Toshihide of the 2008 Nobel Prize for Physics Kobayashi and Maskawa shared half the prize for their discovery of the origin of broken symmetry which created at least six quarks Kohlrausch Friedrich Wilhelm Georg German physicist who investigated the properties of electrolytes substances that conduct electricity in solutions by transfer of ions and contributed to the understanding of their behaviour Kohlrausch was a professor of physics at the universities Kohn Walter Austrian born American physicist who with John A Pople received the 1998

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  • Physics - 6 | Britannica.com
    Although optical microscopes are the subject of this article an image Milankovitch Milutin Serbian mathematician and geophysicist best known for his work that linked long term changes in climate to astronomical factors affecting the amount of solar energy received at Earth s surface His ideas were published in a series of papers and eventually Millikan Robert Andrews American physicist honoured with the Nobel Prize for Physics in 1923 for his study of the elementary electronic charge and the photoelectric effect Millikan graduated from Oberlin College Oberlin Ohio in 1891 and obtained his doctorate at Columbia Milne Edward Arthur English astrophysicist and cosmologist best known for his development of kinematic relativity Milne was educated at the University of Cambridge and served as assistant director of the Solar Physics Observatory at Cambridge from 1920 to 1924 He then mineral processing art of treating crude ores and mineral products in order to separate the valuable minerals from the waste rock or gangue It is the first process that most ores undergo after mining in order to provide a more concentrated material for the procedures Minnaert Marcel Gilles Jozef Flemish astronomer and solar physicist who pioneered in solar spectrophotometry and showed how such a technique could reveal much about the structure of the Sun s outer layers Minnaert was first a botanist but his desire to understand more fully the mirror any polished surface that diverts a ray of light according to the law of reflection The typical mirror is a sheet of glass that is coated on its back with aluminum or silver that produces images by reflection The mirrors used in Greco Roman antiquity Mohorovičić Andrija Croatian meteorologist and geophysicist who discovered the boundary between the Earth s crust and mantle a boundary subsequently named the Mohorovičić discontinuity The son of a shipyard carpenter he was a precocious youth and by the age of 15 spoke molar gas constant symbol R fundamental physical constant arising in the formulation of the general gas law For an ideal gas approximated by most real gases that are not highly compressed or not near the point of liquefaction the pressure p times the volume V of momentum conservation of general law of physics according to which the quantity called momentum that characterizes motion never changes in an isolated collection of objects that is the total momentum of a system remains constant Momentum is equal to the mass of an object Monge Gaspard comte de Péluse French mathematician who invented descriptive geometry the study of the mathematical principles of representing three dimensional objects in a two dimensional plane no longer an active discipline in mathematics the subject is part of mechanical and Moseley Henry Gwyn Jeffreys English physicist who experimentally demonstrated that the major properties of an element are determined by the atomic number not by the atomic weight and firmly established the relationship between atomic number and the charge of the atomic nucleus Mössbauer Rudolf Ludwig German physicist and winner with Robert Hofstadter of the United States of the Nobel Prize for Physics in 1961 for his discovery of the Mössbauer effect Mössbauer discovered the effect in 1957 one year before he received his doctorate from the Technical Mott Sir Nevill F English physicist who shared with P W Anderson and J H Van Vleck of the United States the Nobel Prize for Physics in 1977 for his independent researches on the magnetic and electrical properties of noncrystalline or amorphous semiconductors Mott Mottelson Ben R American Danish physicist who shared the 1975 Nobel Prize for Physics with Aage N Bohr and James Rainwater for his work in determining the asymmetrical shapes of certain atomic nuclei and the reasons behind such asymmetries Having taken his doctorate Müller Erwin Wilhelm German U S physicist who originated field emission microscopy Besides working on solid surface phenomena and gas discharge Müller studied field electron and field ion emissions inventing the field emission microscope 1937 and the field ion microscope Müller Karl Alex Swiss physicist who along with J Georg Bednorz was awarded the 1987 Nobel Prize for Physics for their joint discovery of superconductivity in certain substances at higher temperatures than had previously been thought attainable Müller received his Mulliken Robert Sanderson American chemist and physicist who received the 1966 Nobel Prize for Chemistry for fundamental work concerning chemical bonds and the electronic structure of molecules A graduate of the Massachusetts Institute of Technology Mulliken worked during Munk Walter Austrian born American oceanographer whose pioneering studies of ocean currents and wave propagation laid the foundations for contemporary oceanography The child of a wealthy family Munk was born and raised in Vienna He moved to Lake George N Y Munsell colour system method of designating colours based on a colour arrangement scheme developed by the American art instructor and painter A lbert H Munsell It defines colours by measured scales of hue value and chroma which correspond respectively to dominant wavelength musical sound any tone with characteristics such as controlled pitch and timbre The sounds are produced by instruments in which the periodic vibrations can be controlled by the performer That some sounds are intrinsically musical while others are not is an oversimplification Musschenbroek Pieter van Dutch mathematician and physicist who discovered the principle of the Leyden jar about the same time 1745 as E G von Kleist of Pomerania Musschenbroek a gifted and influential teacher of science held professorships at the universities of Duisburg Nambu Yoichiro Japanese born American physicist who was awarded with Kobayashi Makoto and Maskawa Toshihide the 2008 Nobel Prize for Physics Nambu received half of the prize for his discovery of spontaneous broken symmetry in subatomic physics which explained why Néel Louis Eugène Félix French physicist who was corecipient with the Swedish astrophysicist Hannes Alfvén of the Nobel Prize for Physics in 1970 for his pioneering studies of the magnetic properties of solids His contributions to solid state physics have found numerous Neher Erwin German physicist winner with Bert Sakmann in 1991 of the Nobel Prize

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  • Physics - 7 | Britannica.com
    Rabi Isidor Isaac American physicist who was awarded the Nobel Prize for Physics in 1944 for his invention in 1937 of the atomic and molecular beam magnetic resonance method of observing atomic spectra Rabi s parents settled in New York City in 1899 After earning radio astronomy study of celestial bodies by examination of the radio frequency energy they emit or reflect Radio waves penetrate much of the gas and dust in space as well as the clouds of planetary atmospheres and pass through Earth s atmosphere with little distortion radioactivity property exhibited by certain types of matter of emitting energy and subatomic particles spontaneously It is in essence an attribute of individual atomic nuclei An unstable nucleus will decompose spontaneously or decay into a more stable configuration Rainwater James American physicist who won a share of the Nobel Prize for Physics in 1975 for his part in determining the asymmetrical shapes of certain atomic nuclei Educated at the California Institute of Technology Pasadena and Columbia University where he received Ramakrishnan Venkatraman Indian born physicist and molecular biologist who was awarded the 2009 Nobel Prize for Chemistry along with American biophysicist and biochemist Thomas Steitz and Israeli protein crystallographer Ada Yonath for his research into the atomic structure Raman Sir Chandrasekhara Venkata Indian physicist whose work was influential in the growth of science in India He was the recipient of the Nobel Prize for Physics in 1930 for the discovery that when light traverses a transparent material some of the light that is deflected changes Ramsey Norman Foster American physicist who received one half of the Nobel Prize for Physics in 1989 for his development of a technique to induce atoms to shift from one specific energy level to another The other half of the prize was awarded to Wolfgang Paul and Hans Rankine William John Macquorn Scottish engineer and physicist and one of the founders of the science of thermodynamics particularly in reference to steam engine theory Trained as a civil engineer under Sir John Benjamin MacNeill Rankine was appointed to the Queen Victoria chair Rayleigh John William Strutt 3rd Baron English physical scientist who made fundamental discoveries in the fields of acoustics and optics that are basic to the theory of wave propagation in fluids He received the Nobel Prize for Physics in 1904 for his successful isolation of argon an inert reflection abrupt change in the direction of propagation of a wave that strikes the boundary between different mediums At least part of the oncoming wave disturbance remains in the same medium Regular reflection which follows a simple law occurs at plane boundaries refraction in physics the change in direction of a wave passing from one medium to another caused by its change in speed For example waves in deep water travel faster than in shallow If an ocean wave approaches a beach obliquely the part of the wave farther refrigeration the process of removing heat from an enclosed space or from a substance for the purpose of lowering the temperature In the industrialized nations and affluent regions in the developing world refrigeration is chiefly used to store foodstuffs at low Regnault Henri Victor French chemist and physicist noted for his work on the properties of gases After studying with Justus von Liebig in Giessen Regnault became professor of chemistry successively at the University of Lyon the École Polytechnique 1840 and the Collège Reines Frederick American physicist who was awarded the 1995 Nobel Prize for Physics for his discovery 40 years earlier together with his colleague Clyde L Cowan Jr of the subatomic particle called the neutrino a tiny lepton with little or no mass and a neutral Reis Johann Philipp German physicist who constructed a precursor of the electric telephone Reis was educated at Frankfurt am Main became a merchant for a few years and in 1858 began teaching in Friedrichsdorf While there he experimented with electricity and worked on relative aperture the measure of the light gathering power of an optical system It is expressed in different ways according to the instrument involved The relative aperture for a microscope is called the numerical aperture NA and is equal to the sine of half the angle relativistic mechanics science concerned with the motion of bodies whose relative velocities approach the speed of light c or whose kinetic energies are comparable with the product of their masses m and the square of the velocity of light or mc 2 Such bodies are said to relativity wide ranging physical theories formed by the German born physicist Albert Einstein With his theories of special relativity 1905 and general relativity 1915 Einstein overthrew many assumptions underlying earlier physical theories redefining in renormalization the procedure in quantum field theory by which divergent parts of a calculation leading to nonsensical infinite results are absorbed by redefinition into a few measurable quantities so yielding finite answers Quantum field theory which is used to resonator acoustical device for reinforcing sound as the sounding board of a piano the belly of a stringed instrument the air mass of an organ pipe and the throat nose and mouth cavities of a vocal animal In addition to augmenting acoustic power resonators Reynolds Osborne British engineer physicist and educator best known for his work in hydraulics and hydrodynamics Reynolds was born into a family of Anglican clerics He gained early workshop experience by apprenticing with a mechanical engineer and he graduated at Richardson Lewis Fry British physicist and psychologist who was the first to apply mathematical techniques to predict the weather accurately Richardson made major contributions to methods of solving certain types of problems in physics and from 1913 to 1922 he applied Richardson Robert C American physicist who was the corecipient along with Douglas Osheroff and David Lee of the 1996 Nobel Prize for Physics for their discovery of superfluidity in the isotope helium 3 3 He Richardson received a Ph D in physics from Duke University Richardson Sir Owen Willans English physicist and recipient of the

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  • Physics - 8 | Britannica.com
    established figure Steinberger Jack German born American physicist who along with Leon M Lederman and Melvin Schwartz was awarded the Nobel Prize for Physics in 1988 for their joint discoveries concerning neutrinos Steinberger immigrated to the United States in 1934 He studied physics Steinheil Karl August German physicist who did pioneering work in telegraphy optics and photometry Steinheil received the Ph D at Königsberg in 1825 and in 1832 began to teach physics and mathematics at Munich University From 1849 to 1852 he organized the Austrian telegraph Steitz Thomas American biophysicist and biochemist who was awarded the 2009 Nobel Prize for Chemistry along with Indian born American physicist and molecular biologist Venkatraman Ramakrishnan and Israeli protein crystallographer Ada Yonath for his research into stereoscopy science and technology dealing with two dimensional drawings or photographs that when viewed by both eyes appear to exist in three dimensions in space A popular term for stereoscopy is 3 D Stereoscopic pictures are produced in pairs the members of Stern Otto German born scientist and winner of the Nobel Prize for Physics in 1943 for his development of the molecular beam as a tool for studying the characteristics of molecules and for his measurement of the magnetic moment of the proton Stern s early scientific Stewart Balfour Scottish meteorologist and geophysicist noted for his studies of terrestrial magnetism and radiant heat Stewart pursued a mercantile career for 10 years before becoming an assistant at Kew Observatory and later an assistant to James Forbes at Edinburgh Stokes Sir George Gabriel 1st Baronet British physicist and mathematician noted for his studies of the behaviour of viscous fluids particularly for his law of viscosity which describes the motion of a solid sphere in a fluid and for Stokes s theorem a basic theorem of vector analysis Stoney George Johnstone physicist who introduced the term electron for the fundamental unit of electricity In 1848 Stoney became assistant to the astronomer William Parsons Rosse who secured for him a professorship in natural philosophy natural science at Queen s College Størmer Fredrik Norwegian geophysicist and mathematician who developed a mathematical theory of auroral phenomena Professor of pure mathematics at the University of Christiania Oslo after 1924 from 1903 to 1946 Størmer began his mathematical work with studies of Störmer Horst L German born American physicist who with Daniel C Tsui and Robert B Laughlin was coawarded the 1998 Nobel Prize in Physics for the discovery and explanation of the fractional quantum Hall effect Störmer graduated from the University of Frankfurt string theory in particle physics a theory that attempts to merge quantum mechanics with Albert Einstein s general theory of relativity The name string theory comes from the modeling of subatomic particles as tiny one dimensional stringlike entities rather than Strömgren Bengt Danish astrophysicist who pioneered the present day knowledge of the gas clouds in space Son of the noted Swedish born Danish astronomer Svante Elis Strömgren he early developed an interest in astronomy He collaborated with his father on several works sunlight solar radiation that is visible at Earth s surface The amount of sunlight is dependent on the extent of the daytime cloud cover Some places on Earth receive more than 4 000 hours per year of sunlight more than 90 percent of the maximum possible Sunyaev Rashid Russian German astrophysicist who with Soviet physicist Yakov Zeldovich first proposed the Sunyaev Zeldovich SZ effect in which distortions in the cosmic microwave background CMB are caused by clusters of galaxies With Russian astrophysicist supergravity a type of quantum field theory of elementary subatomic particles and their interactions that is based on the particle symmetry known as supersymmetry and that naturally includes the gravitational force along with the other fundamental interactions of supersymmetry in particle physics a symmetry between fermions subatomic particles with half integer values of intrinsic angular momentum or spin and bosons particles with integer values of spin Supersymmetry is a complex mathematical framework based on the Swan Sir Joseph Wilson English physicist and chemist who produced an early electric lightbulb and invented the dry photographic plate an important improvement in photography and a step in the development of modern photographic film After serving his apprenticeship with a Swedenborg Emanuel Swedish scientist Christian mystic philosopher and theologian who wrote voluminously in interpreting the Scriptures as the immediate word of God Soon after his death devoted followers created Swedenborgian societies dedicated to the study of his Swings Pol Belgian astrophysicist noted for his spectroscopic studies of the composition and structure of stars and comets In 1932 Swings was appointed professor of spectroscopy and astrophysics at his alma mater the University of Liège Belgium he taught there symmetry in physics the concept that the properties of particles such as atoms and molecules remain unchanged after being subjected to a variety of symmetry transformations or operations Since the earliest days of natural philosophy Pythagoras in the 6th Szilard Leo Hungarian born American physicist who helped conduct the first sustained nuclear chain reaction and was instrumental in initiating the Manhattan Project for the development of the atomic bomb In 1922 Szilard received his Ph D from the University of Tait Peter Guthrie Scottish physicist and mathematician who helped develop quaternions an advanced algebra that gave rise to vector analysis and was instrumental in the development of modern mathematical physics After serving from 1852 to 1854 as a fellow and lecturer Tamm Igor Yevgenyevich Soviet physicist who shared the 1958 Nobel Prize for Physics with Pavel A Cherenkov and Ilya M Frank for his efforts in explaining Cherenkov radiation Tamm was one of the theoretical physicists who contributed to the construction of the first Soviet Taylor Albert Hoyt American physicist and radio engineer whose work underlay the development of radar in the United States Taylor was trained at Northwestern University Evanston Illinois and the University of Göttingen Germany He taught at Michigan State College Taylor Joseph H Jr American radio astronomer and physicist who with Russell A Hulse was the corecipient of the

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  • Physics - 9 | Britannica.com
    bridge a device that accurately measured electrical resistance and became widely used in laboratories Wheatstone was appointed professor of experimental philosophy at King s College London in 1834 Wheeler John Archibald physicist the first American involved in the theoretical development of the atomic bomb He also originated a novel approach to the unified field theory and popularized the term black hole Wheeler who was the son of librarians first became interested white noise in music the effect of the complete range of audible sound wave frequencies heard simultaneously analogous to white light which contains all the frequencies of the light spectrum The sound of cymbals and snare drums has white noise characteristics Wieman Carl E American physicist who with Eric A Cornell and Wolfgang Ketterle won the Nobel Prize for Physics in 2001 for creating a new ultracold state of matter the so called Bose Einstein condensate BEC After studying at the Massachusetts Institute of Technology Wien Wilhelm German physicist who received the Nobel Prize for Physics in 1911 for his displacement law concerning the radiation emitted by the perfectly efficient blackbody a surface that absorbs all radiant energy falling on it Wien obtained his doctorate at Wigner Eugene Hungarian born American physicist joint winner with J Hans D Jensen of West Germany and Maria Goeppert Mayer of the United States of the Nobel Prize for Physics in 1963 He received the prize for his many contributions to nuclear physics which Wilczek Frank American physicist who with David J Gross and H David Politzer was awarded the Nobel Prize for Physics in 2004 for discoveries regarding the strong force the nuclear force that binds together quarks the smallest building blocks of matter and holds Wilkins Maurice New Zealand born British biophysicist whose X ray diffraction studies of deoxyribonucleic acid DNA proved crucial to the determination of DNA s molecular structure by James D Watson and Francis Crick For this work the three scientists were jointly Wilson C T R Scottish physicist who with Arthur H Compton received the Nobel Prize for Physics in 1927 for his invention of the Wilson cloud chamber which became widely used in the study of radioactivity X rays cosmic rays and other nuclear phenomena Wilson Wilson J Tuzo Canadian geologist and geophysicist who established global patterns of faulting and the structure of the continents His studies in plate tectonics had an important bearing on the theories of continental drift seafloor spreading and convection currents Wilson Kenneth Geddes American physicist who was awarded the 1982 Nobel Prize for Physics for his development of a general procedure for constructing improved theories concerning the transformations of matter called continuous or second order phase transitions Wilson graduated Wilson Raymond Neil British physicist who pioneered the field of active optics Wilson received a bachelor s degree in physics from Birmingham University He received a doctoral degree from Imperial College in London In 1961 he joined the German optical firm Carl Zeiss Wilson Robert Woodrow American radio astronomer who shared with

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  • Cereals | Britannica.com
    were not generally adopted until the 1930s when corn Zea mays in agriculture cereal plant of the tribe Maydeae of the grass family Poaceae originating in the Americas and its edible grain Since its introduction into Europe by Columbus and other explorers corn has spread to all areas of the world suitable Corn Law in English history any of the regulations governing the import and export of grain Records mention the imposition of Corn Laws as early as the 12th century The laws became politically important in the late 18th century and the first half of the 19th East Edward Murray American plant geneticist botanist agronomist and chemist whose experiments along with those of others led to the development of hybrid corn maize He was particularly interested in determining and controlling the protein and fat content of corn Evans Oliver American inventor who pioneered the high pressure steam engine U S patent 1790 and created the first continuous production line 1784 Evans was apprenticed to a wheelwright at the age of 16 Observing the trick of a blacksmith s boy who used the Farrer William James British born Australian agricultural researcher who developed several varieties of drought and rust resistant wheat that made possible a great expansion of Australia s wheat belt Farrer settled in Australia in 1870 In 1875 he was licensed as a surveyor flour finely ground cereal grains or other starchy portions of plants used in various food products and as a basic ingredient of baked goods Flour made from wheat grains is the most satisfactory type for baked products that require spongy structure In modern Granger movement coalition of U S farmers particularly in the Middle West that fought monopolistic grain transport practices during the decade following the American Civil War The Granger movement began with

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  • Ferns and Other Lower Vascular Plants | Britannica.com
    especially the ferns contributed greatly to a modern emphasis on the study of the origins and evolutionary development of these plants He is best known for his interpolation theory explaining the bracken Pteridium aquilinum a member of the fern family Dennstaedtiaceae plant division Pteridophyta widely distributed throughout the world in temperate and tropical regions Pteridium aquilinum is usually separated into 12 varieties or subspecies Some Campbell Douglas Houghton American botanist known for his research concerning modes of sexual reproduction in mosses and ferns His work intensified a controversy surrounding the evolutionary origin of the Tracheophyta vascular plants A professor of botany at Indiana University cliff brake Pellaea any of about 40 species of ferns of the genus Pellaea family Pteridaceae Cliff brake ferns grow on or among rocks mostly limestone throughout the world Small plants with mostly leathery leaves they are characterized by spore bearing structures club moss common name for plants in the family Lycopodiaceae which contains the genera Huperzia 300 species Lycopodiella 40 species and Lycopodium 40 species though some botanists split up these genera into 10 or more genera The plants are mainly native Davalliaceae the hanging fern family containing 4 5 genera and 65 species in the division Pteridophyta the lower vascular plants The family is mostly restricted to tropical regions especially in the Old World Most of the species are epiphytes with long creeping Dennstaedtiaceae the bracken fern family containing 11 genera and 170 species in the division Pteridophyta the lower vascular plants Dennstaedtiaceae is distributed nearly worldwide although the family is most diverse in tropical regions it is well represented Dicksoniaceae the tree fern family containing about 3 genera and some 30 species in the division Pteridophyta the lower vascular plants The family has a long and diverse fossil record extending back to the Triassic Period 251 million to 199 6 million years ago Dipteridaceae the umbrella fern family in the division Pteridophyta the lower vascular plants The family has a long fossil history dating back to the Triassic Period 251 million to 199 6 million years ago but it presently contains only two extant genera Dipteris Dryopteridaceae the shield fern family containing 40 50 genera and about 1 700 species in the division Pteridophyta the lower vascular plants Dryopteridaceae are distributed nearly worldwide but are most diverse in temperate regions and in mountainous areas in Equisetopsida division Pteridophyta class of primitive spore bearing vascular plants Most members of the group are extinct and known only from their fossilized remains The sole living genus Equisetum order Equisetales is made up of 15 species of very ancient fern any of several nonflowering vascular plants that possess true roots stems and complex leaves and that reproduce by spores They belong to the lower vascular plant division Pteridophyta having leaves usually with branching vein systems the young leaves Gleicheniaceae the forking fern family containing 6 genera and about 125 species in the division Pteridophyta the lower vascular plants This relatively primitive family has a long fossil history

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  • Flowering Plants | Britannica.com
    its edible fruit Ackee and salt fish is a popular dish in the Caribbean and is the national dish of Jamaica Acorales the sweet flag order of flowering plants and the most basal lineage among the monocotyledons monocots which are characterized by having a single seed leaf This order contains the single family Acoraceae and one genus Acorus which comprises two African violet Saintpaulia any of the six species of flowering plants in the genus Saintpaulia family Gesneriaceae Native to higher elevations in tropical eastern Africa African violets are widely grown horticulturally especially S ionantha The members of Saintpaulia Agavoideae the agave subfamily of the flowering plant family Asparagaceae order Asparagales consisting of 23 genera and 637 species of short stemmed often woody plants distributed throughout tropical subtropical and temperate areas of the world Though formerly agrimony Agrimonia genus of some 12 15 species of perennial herbs in the rose family Rosaceae Agrimony species are found primarily in the Northern Hemisphere and have historically been used in folk medicine Physical description Agrimony plants are typically akund floss downy seed fibre obtained from Calotropis procera and C gigantea milkweed plants of the Apocynaceae family formerly in Asclepiadaceae Small trees or shrubs these two species are native to southern Asia and Africa and were introduced to South America Albizia large genus of trees of the pea family Fabaceae native to warm regions of the Old World The alternate compound leaves are bipinnate i e the leaflets of the feather formed leaves in turn bear leaflets The small flowers are borne in globular alder any of about 30 species of ornamental shrubs and trees constituting the genus Alnus in the birch family Betulaceae distributed throughout the Northern Hemisphere and western South America on cool wet sites at elevations up to 2 500 m 8 200 feet alder buckthorn Rhamnus frangula woody shrub or small tree of the buckthorn family Rhamnaceae native to western Asia Europe and northern Africa It has been introduced into North America and other regions where it is often cultivated as an ornamental The plant alfalfa Medicago sativa perennial cloverlike leguminous plant of the pea family Fabaceae known for its tolerance of drought heat and cold for the remarkable productivity and quality of its herbage and for its value in soil improvement It is widely Alismataceae the water plantain family of 113 species of freshwater flowering plants belonging to the order Alismatales and including 17 genera the most common of which are Alisma water plantain Echinodorus burhead and Sagittaria arrowhead Most members Alismatales arrowhead and pondweed order of flowering plants belonging to the monocotyledon monocot group whose species have a single seed leaf Most of the some 4 500 species are aquatic and grow submersed or partially exposed to the air in marshes and other alizarin a red dye originally obtained from the root of the common madder plant Rubia tinctorum in which it occurs combined with the sugars xylose and glucose The cultivation of madder and the use of

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