In botany, phyllotaxis or phyllotaxy is the arrangement of leaves on a plant stem. Phyllotactic spirals form a distinctive class of patterns in nature; the term was coined by Charles Bonnet to describe the arrangement of leaves on a plant. The basic arrangements of leaves on a stem are alternate. Leaves may be whorled if several leaves arise, or appear to arise, from the same level on a stem. With an opposite leaf arrangement, two leaves arise from the stem at the same level, on opposite sides of the stem. An opposite leaf pair can be thought of as a whorl of two leaves. With an alternate pattern, each leaf arises at a different point on the stem. Distichous phyllotaxis called "two-ranked leaf arrangement" is a special case of either opposite or alternate leaf arrangement where the leaves on a stem are arranged in two vertical columns on opposite sides of the stem. Examples include various bulbous plants such as Boophone, it occurs in other plant habits such as those of Gasteria or Aloe seedlings, in mature plants of related species such as Kumara plicatilis.
In an opposite pattern, if successive leaf pairs are 90 degrees apart, this habit is called decussate. It is common in members of the family Crassulaceae Decussate phyllotaxis occurs in the Aizoaceae. In genera of the Aizoaceae, such as Lithops and Conophytum, many species have just two developed leaves at a time, the older pair folding back and dying off to make room for the decussately oriented new pair as the plant grows; the whorled arrangement is unusual on plants except for those with short internodes. Examples of trees with whorled phyllotaxis are Brabejum stellatifolium and the related genus Macadamia. A whorl can occur as a basal structure where all the leaves are attached at the base of the shoot and the internodes are small or nonexistent. A basal whorl with a large number of leaves spread out in a circle is called a rosette; the rotational angle from leaf to leaf in a repeating spiral can be represented by a fraction of a full rotation around the stem. Alternate distichous leaves will have an angle of 1/2 of a full rotation.
In beech and hazel the angle is 1/3, in oak and apricot it is 2/5, in sunflowers and pear, it is 3/8, in willow and almond the angle is 5/13. The numerator and denominator consist of a Fibonacci number and its second successor; the number of leaves is sometimes called rank, in the case of simple Fibonacci ratios, because the leaves line up in vertical rows. With larger Fibonacci pairs, the pattern becomes non-repeating; this tends to occur with a basal configuration. Examples can be found in composite flowers and seed heads; the most famous example is the sunflower head. This phyllotactic pattern creates an optical effect of criss-crossing spirals. In the botanical literature, these designs are described by the number of counter-clockwise spirals and the number of clockwise spirals; these turn out to be Fibonacci numbers. In some cases, the numbers appear to be multiples of Fibonacci numbers because the spirals consist of whorls; the pattern of leaves on a plant is controlled by the local depletion of the plant hormone auxin in certain areas of the meristem.
Leaves become initiated in localized areas. When a leaf is initiated and begins development, auxin begins to flow towards it, thus depleting auxin from another area on the meristem where a new leaf is to be initiated; this gives rise to a self-propagating system, controlled by the ebb and flow of auxin in different regions of the meristematic topography. Insight into the mechanism had to wait until Wilhelm Hofmeister proposed a model in 1868. A primordium, the nascent leaf, forms at the least crowded part of the shoot meristem; the golden angle between successive leaves is the blind result of this jostling. Since three golden arcs add up to more than enough to wrap a circle, this guarantees that no two leaves follow the same radial line from center to edge; the generative spiral is a consequence of the same process that produces the clockwise and counter-clockwise spirals that emerge in densely packed plant structures, such as Protea flower disks or pinecone scales. In modern times, researchers such as Snow and Snow have continued these lines of inquiry.
Computer modeling and morphological studies have refined Hoffmeister's ideas. Questions remain about the details. Botanists are divided on whether the control of leaf migration depends on chemical gradients among the primordia or purely mechanical forces. Lucas rather than Fibonacci numbers have been observed in a few plants and the leaf positioning appears to be random. Physical models of phyllotaxis date back to Airy's experiment of packing hard spheres. Gerrit van Iterson diagrammed. Douady et al. showed that phyllotactic patterns emerge as self-organizing processes in dynamic systems. In 1991, Levitov proposed that lowest energy configurations of repulsive particles in cylindrical geometries reproduce the spirals of botanical phyllotaxis. More Nisoli et al. showed that to be true by constructing a "magnetic cactus" made of magnetic dipoles mounted on bearings stacked along a "stem". They demonstrated that these interacting particles can access novel dynamical phenomena beyond what botany yields: a "Dynamical Phyllotaxis" family of non local topological solitons emerge in the nonlinear regime of these systems, as well as purely classical rotons and maxons in the spectrum of linear excitations.
Close packing of spheres generates a dodecahedral tessellation with pentaprismic fac
In botany, shoots consist of stems including their appendages, the leaves and lateral buds, flowering stems and flower buds. The new growth from seed germination that grows upward is a shoot. In the spring, perennial plant shoots are the new growth that grows from the ground in herbaceous plants or the new stem or flower growth that grows on woody plants. In everyday speech, shoots are synonymous with stems. Stems, which are an integral component of shoots, provide an axis for buds and leaves. Young shoots are eaten by animals because the fibres in the new growth have not yet completed secondary cell wall development, making the young shoots softer and easier to chew and digest; as shoots grow and age, the cells develop secondary cell walls that have a tough structure. Some plants produce toxins that make their shoots less palatable. Many woody plants have long shoots. In some angiosperms, the short shoots called spur shoots or fruit spurs, produce the majority of flowers and fruit. A similar pattern occurs in some conifers and in Ginkgo, although the "short shoots" of some genera such as Picea are so small that they can be mistaken for part of the leaf that they have produced.
A related phenomenon is seasonal heterophylly, which involves visibly different leaves from spring growth and lammas growth. Whereas spring growth comes from buds formed the previous season, includes flowers, lammas growth involves long shoots. Bud Heteroblasty, abrupt change in the growth pattern of some plants as they mature Lateral shoot Sterigma, the "woody peg" below the leaf of some conifers Thorn, true thorns, as distinct from spines or prickles, are short shoots
A region is arid when it is characterized by a severe lack of available water, to the extent of hindering or preventing the growth and development of plant and animal life. Environments subject to arid climates are called xeric or desertic. Most "arid" climates straddle the Equator; the distribution of aridity observed at any one point in time is the result of the general circulation of the atmosphere. The latter does change over time through climate change. For example, temperature increase across the Nile Basin over the next 30–40 years could change the region from semi-arid to arid, resulting in a significant reduction in agricultural land. In addition, changes in land use can result in greater demands on soil water and induce a higher degree of aridity. Aridity index Arid Forest Research Institute Desert climate Desiccation tolerance Drought Relative humidity Saturation vapor pressure Griffiths, J. F.'Climatology', Chapter 2 in Handbook of Applied Meteorology, Edited by David D. Houghton, John Wiley and Sons, ISBN 0-471-08404-2.
Durrenberger, R. W.'Arid Climates', article in The Encyclopedia of Climatology, p. 92-101, Edited by J. E. Oliver and R. W. Fairbridge, Van Nostrand Reinhold Company, New York, ISBN 0-87933-009-0. Stadler, S. J'Aridity Indexes', article in The Encyclopedia of Climatology, p. 102-107, Edited by J. E. Oliver and R. W. Fairbridge, Van Nostrand Reinhold Company, New York, ISBN 0-87933-009-0. Blue Peace for the Nile Report, 2009, Strategic Foresight Group
In botany, a bud is an undeveloped or embryonic shoot and occurs in the axil of a leaf or at the tip of a stem. Once formed, a bud may remain for some time in a dormant condition, or it may form a shoot immediately. Buds may be specialized to develop flowers or short shoots, or may have the potential for general shoot development; the term bud is used in zoology, where it refers to an outgrowth from the body which can develop into a new individual. The buds of many woody plants in temperate or cold climates, are protected by a covering of modified leaves called scales which enclose the more delicate parts of the bud. Many bud scales are covered by a gummy substance; when the bud develops, the scales may enlarge somewhat but just drop off, leaving a series of horizontally-elongated scars on the surface of the growing stem. By means of these scars one can determine the age of any young branch, since each year's growth ends in the formation of a bud, the formation of which produces an additional group of bud scale scars.
Continued growth of the branch causes these scars to be obliterated after a few years so that the total age of older branches cannot be determined by this means. In many plants scales do not form over the bud, the bud is called a naked bud; the minute underdeveloped leaves in such buds are excessively hairy. Naked buds are found in some shrubs, like some species of the Sumac and Viburnums and in herbaceous plants. In many of the latter, buds are more reduced consisting of undifferentiated masses of cells in the axils of leaves. A terminal bud occurs on the end of a stem and lateral buds are found on the side. A head of cabbage is an exceptionally large terminal bud, while Brussels sprouts are large lateral buds. Since buds are formed in the axils of leaves, their distribution on the stem is the same as that of leaves. There are alternate and whorled buds, as well as the terminal bud at the tip of the stem. In many plants buds appear in unexpected places: these are known as adventitious buds, it is possible to find a bud in a remarkable series of gradations of bud scales.
In the buckeye, for example, one may see a complete gradation from the small brown outer scale through larger scales which on unfolding become somewhat green to the inner scales of the bud, which are remarkably leaf-like. Such a series suggests that the scales of the bud are in truth leaves, modified to protect the more delicate parts of the plant during unfavorable periods. Buds are useful in the identification of plants for woody plants in winter when leaves have fallen. Buds may be classified and described according to different criteria: location, status and function. Botanists use the following terms: for location: terminal, when located at the tip of a stem; the term is usable as a synonym of resting, but is better employed for buds waiting undeveloped for years, for example epicormic buds. Buds The term bud is used by analogy within zoology as well, where it refers to an outgrowth from the body which develops into a new individual, it is a form of asexual reproduction limited to animals or plants of simple structure.
In this process a portion of the wall of the parent cell pushes out. The protuberance thus formed enlarges while at this time the nucleus of the parent cell divides. One of the resulting nuclei passes into the bud, the bud is cut off from its parent cell and the process is repeated; the daughter cell will begin to bud before it becomes separated from the parent, so that whole colonies of adhering cells may be formed. Cross walls cut off the bud from the original cell
Botany called plant science, plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist; the term "botany" comes from the Ancient Greek word βοτάνη meaning "pasture", "grass", or "fodder". Traditionally, botany has included the study of fungi and algae by mycologists and phycologists with the study of these three groups of organisms remaining within the sphere of interest of the International Botanical Congress. Nowadays, botanists study 410,000 species of land plants of which some 391,000 species are vascular plants, 20,000 are bryophytes. Botany originated in prehistory as herbalism with the efforts of early humans to identify – and cultivate – edible and poisonous plants, making it one of the oldest branches of science. Medieval physic gardens attached to monasteries, contained plants of medical importance, they were forerunners of the first botanical gardens attached to universities, founded from the 1540s onwards.
One of the earliest was the Padua botanical garden. These gardens facilitated the academic study of plants. Efforts to catalogue and describe their collections were the beginnings of plant taxonomy, led in 1753 to the binomial system of Carl Linnaeus that remains in use to this day. In the 19th and 20th centuries, new techniques were developed for the study of plants, including methods of optical microscopy and live cell imaging, electron microscopy, analysis of chromosome number, plant chemistry and the structure and function of enzymes and other proteins. In the last two decades of the 20th century, botanists exploited the techniques of molecular genetic analysis, including genomics and proteomics and DNA sequences to classify plants more accurately. Modern botany is a broad, multidisciplinary subject with inputs from most other areas of science and technology. Research topics include the study of plant structure and differentiation, reproduction and primary metabolism, chemical products, diseases, evolutionary relationships and plant taxonomy.
Dominant themes in 21st century plant science are molecular genetics and epigenetics, which are the mechanisms and control of gene expression during differentiation of plant cells and tissues. Botanical research has diverse applications in providing staple foods, materials such as timber, rubber and drugs, in modern horticulture and forestry, plant propagation and genetic modification, in the synthesis of chemicals and raw materials for construction and energy production, in environmental management, the maintenance of biodiversity. Botany originated as the study and use of plants for their medicinal properties. Many records of the Holocene period date early botanical knowledge as far back as 10,000 years ago; this early unrecorded knowledge of plants was discovered in ancient sites of human occupation within Tennessee, which make up much of the Cherokee land today. The early recorded history of botany includes many ancient writings and plant classifications. Examples of early botanical works have been found in ancient texts from India dating back to before 1100 BC, in archaic Avestan writings, in works from China before it was unified in 221 BC.
Modern botany traces its roots back to Ancient Greece to Theophrastus, a student of Aristotle who invented and described many of its principles and is regarded in the scientific community as the "Father of Botany". His major works, Enquiry into Plants and On the Causes of Plants, constitute the most important contributions to botanical science until the Middle Ages seventeen centuries later. Another work from Ancient Greece that made an early impact on botany is De Materia Medica, a five-volume encyclopedia about herbal medicine written in the middle of the first century by Greek physician and pharmacologist Pedanius Dioscorides. De Materia Medica was read for more than 1,500 years. Important contributions from the medieval Muslim world include Ibn Wahshiyya's Nabatean Agriculture, Abū Ḥanīfa Dīnawarī's the Book of Plants, Ibn Bassal's The Classification of Soils. In the early 13th century, Abu al-Abbas al-Nabati, Ibn al-Baitar wrote on botany in a systematic and scientific manner. In the mid-16th century, "botanical gardens" were founded in a number of Italian universities – the Padua botanical garden in 1545 is considered to be the first, still in its original location.
These gardens continued the practical value of earlier "physic gardens" associated with monasteries, in which plants were cultivated for medical use. They supported the growth of botany as an academic subject. Lectures were given about the plants grown in the gardens and their medical uses demonstrated. Botanical gardens came much to northern Europe. Throughout this period, botany remained subordinate to medicine. German physician Leonhart Fuchs was one of "the three German fathers of botany", along with theologian Otto Brunfels and physician Hieronymus Bock. Fuchs and Brunfels broke away from the tradition of copying earlier works to make original observations of their own. Bock created his own system of plant classification. Physician Valerius Cordus authored a botanically and pharmacologically important herbal Historia Plantarum in 1544 and a pharmacopoeia of lasting importance, the Dispensatorium
In botany, the petiole is the stalk that attaches the leaf blade to the stem. Outgrowths appearing on each side of the petiole in some species are called stipules. Leaves lacking a petiole are called epetiolate; the petiole is a stalk. In petiolate leaves, the leaf stalk may be long, as in the leaves of celery and rhubarb, short or absent, in which case the blade attaches directly to the stem and is said to be sessile. Subpetiolate leaves are nearly petiolate, or have an short petiole, may appear sessile; the broomrape family Orobanchaceae is an example of a family. In some other plant groups, such as the speedwell genus Veronica and sessile leaves may occur in different species. In the grasses the leaves are apetiolate, but the leaf blade may be narrowed at the junction with the leaf sheath to form a pseudopetiole, as in Pseudosasa japonica. In plants with compound leaves, the leaflets are attached to a continuation of the petiole called the rachis; each leaflet may be attached to the rachis by a short stalk called the petiolule.
There may be swollen regions at either end of the petiole known as pulvina that are composed of a flexible tissue that allows leaf movement. Pulvina are common in the prayer plant family Marantaceae. A pulvinus on a petiolule is called a pulvinulus. In some plants, the petioles are flattened and widened, to become phyllodes or phyllodia, or cladophylls and the true leaves may be reduced or absent. Thus, the phyllode comes to serve the functions of the leaf. Phyllodes are common in the genus Acacia the Australian species, at one time put in Acacia subgenus Phyllodineae. In Acacia koa, the phyllodes are leathery and thick, allowing the tree to survive stressful environments; the petiole allows submerged hydrophytes to have leaves floating at different depths, the petiole being between the node and the stem. In plants such as rhubarb, celery and cardoons the petioles are cultivated as edible crops; the petiole of rhubarb produces the leaf at its end. Botanically it is culinarily used as a fruit. Petiole comes from Latin petiolus, or peciolus "little foot", "stem", an alternative diminutive of pes "foot".
The regular diminutive pediculus is used for "foot stalk". Hyponastic response Pedicel "Petiole". Collier's New Encyclopedia. 1921
Humidity is the amount of water vapour present in air. Water vapour, the gaseous state of water, is invisible to the human eye. Humidity indicates the likelihood for dew, or fog to be present; the amount of water vapour needed to achieve saturation increases as the temperature increases. As the temperature of a parcel of air decreases it will reach the saturation point without adding or losing water mass; the amount of water vapour contained within a parcel of air can vary significantly. For example, a parcel of air near saturation may contain 28 grams of water per cubic metre of air at 30 °C, but only 8 grams of water per cubic metre of air at 8 °C. Three primary measurements of humidity are employed: absolute and specific. Absolute humidity describes the water content of air and is expressed in either grams per cubic metre or grams per kilogram. Relative humidity, expressed as a percentage, indicates a present state of absolute humidity relative to a maximum humidity given the same temperature.
Specific humidity is the ratio of water vapor mass to total moist air parcel mass. Humidity plays an important role for surface life. For animal life dependent on perspiration to regulate internal body temperature, high humidity impairs heat exchange efficiency by reducing the rate of moisture evaporation from skin surfaces; this effect can be calculated using a heat index table known as a humidex. Absolute humidity is the total mass of water vapor present in mass of air, it does not take temperature into consideration. Absolute humidity in the atmosphere ranges from near zero to 30 grams per cubic metre when the air is saturated at 30 °C. Absolute humidity is the mass of the water vapor, divided by the volume of the air and water vapor mixture, which can be expressed as: A H = m H 2 O V n e t; the absolute humidity changes as air pressure changes, if the volume is not fixed. This makes it unsuitable for chemical engineering calculations, e.g. in drying, where temperature can vary considerably.
As a result, absolute humidity in chemical engineering may refer to mass of water vapor per unit mass of dry air known as the humidity ratio or mass mixing ratio, better suited for heat and mass balance calculations. Mass of water per unit volume as in the equation above is defined as volumetric humidity; because of the potential confusion, British Standard BS 1339 suggests avoiding the term "absolute humidity". Units should always be checked. Many humidity charts are given in g/kg or kg/kg; the field concerned with the study of physical and thermodynamic properties of gas–vapor mixtures is named psychrometrics. The relative humidity of an air-water mixture is defined as the ratio of the partial pressure of water vapor in the mixture to the equilibrium vapor pressure of water over a flat surface of pure water at a given temperature: ϕ = p H 2 O p H 2 O ∗ Relative humidity is expressed as a percentage. Relative humidity is an important metric used in weather forecasts and reports, as it is an indicator of the likelihood of precipitation, dew, or fog.
In hot summer weather, a rise in relative humidity increases the apparent temperature to humans by hindering the evaporation of perspiration from the skin. For example, according to the Heat Index, a relative humidity of 75% at air temperature of 80.0 °F would feel like 83.6 °F ±1.3 °F. Specific humidity is the ratio of the mass of water vapor to the total mass of the moist air parcel. Specific humidity is equal to the mixing ratio, defined as the ratio of the mass of water vapor in an air parcel to the mass of dry air for the same parcel; as temperature decreases, the amount of water vapor needed to reach saturation decreases. As the temperature of a parcel of air becomes lower it will reach the point of saturation without adding or losing water mass. A device used to measure humidity is called a hygrometer. A humidistat is a humidity-triggered switch used to control a dehumidifier. There are various devices used to regulate humidity. Calibration standards for the most accurate measurement include the gravimetric hygrometer, chilled mirror hygrometer, electrolytic hygrometer.
The gravimetric method, while the most accurate, is cumbersome. For fast and accurate measurement the chilled mirror method is effective. For process on-line measurements, the most used sensors nowadays are based on capacitance measurements to measure relative humidity with internal conversions to d