A leaf is an organ of a vascular plant and is the principal lateral appendage of the stem. The leaves and stem together form the shoot. Leaves are collectively referred to as foliage, as in "autumn foliage". A leaf is a thin, dorsiventrally flattened organ borne above ground and specialized for photosynthesis. In most leaves, the primary photosynthetic tissue, the palisade mesophyll, is located on the upper side of the blade or lamina of the leaf but in some species, including the mature foliage of Eucalyptus, palisade mesophyll is present on both sides and the leaves are said to be isobilateral. Most leaves have distinct upper surface and lower surface that differ in colour, the number of stomata, the amount and structure of epicuticular wax and other features. Leaves can have many different shapes and textures; the broad, flat leaves with complex venation of flowering plants are known as megaphylls and the species that bear them, the majority, as broad-leaved or megaphyllous plants. In the clubmosses, with different evolutionary origins, the leaves are simple and are known as microphylls.
Some leaves, such as bulb scales, are not above ground. In many aquatic species the leaves are submerged in water. Succulent plants have thick juicy leaves, but some leaves are without major photosynthetic function and may be dead at maturity, as in some cataphylls and spines. Furthermore, several kinds of leaf-like structures found in vascular plants are not homologous with them. Examples include flattened plant stems called phylloclades and cladodes, flattened leaf stems called phyllodes which differ from leaves both in their structure and origin; some structures of non-vascular plants function much like leaves. Examples include the phyllids of liverworts. Leaves are the most important organs of most vascular plants. Green plants are autotrophic, meaning that they do not obtain food from other living things but instead create their own food by photosynthesis, they capture the energy in sunlight and use it to make simple sugars, such as glucose and sucrose, from carbon dioxide and water. The sugars are stored as starch, further processed by chemical synthesis into more complex organic molecules such as proteins or cellulose, the basic structural material in plant cell walls, or metabolised by cellular respiration to provide chemical energy to run cellular processes.
The leaves draw water from the ground in the transpiration stream through a vascular conducting system known as xylem and obtain carbon dioxide from the atmosphere by diffusion through openings called stomata in the outer covering layer of the leaf, while leaves are orientated to maximise their exposure to sunlight. Once sugar has been synthesized, it needs to be transported to areas of active growth such as the plant shoots and roots. Vascular plants transport sucrose in a special tissue called the phloem; the phloem and xylem are parallel to each other but the transport of materials is in opposite directions. Within the leaf these vascular systems branch to form veins which supply as much of the leaf as possible, ensuring that cells carrying out photosynthesis are close to the transportation system. Leaves are broad and thin, thereby maximising the surface area directly exposed to light and enabling the light to penetrate the tissues and reach the chloroplasts, thus promoting photosynthesis.
They are arranged on the plant so as to expose their surfaces to light as efficiently as possible without shading each other, but there are many exceptions and complications. For instance plants adapted to windy conditions may have pendent leaves, such as in many willows and eucalyptss; the flat, or laminar, shape maximises thermal contact with the surrounding air, promoting cooling. Functionally, in addition to carrying out photosynthesis, the leaf is the principal site of transpiration, providing the energy required to draw the transpiration stream up from the roots, guttation. Many gymnosperms have thin needle-like or scale-like leaves that can be advantageous in cold climates with frequent snow and frost; these are interpreted as reduced from megaphyllous leaves of their Devonian ancestors. Some leaf forms are adapted to modulate the amount of light they absorb to avoid or mitigate excessive heat, ultraviolet damage, or desiccation, or to sacrifice light-absorption efficiency in favour of protection from herbivory.
For xerophytes the major constraint drought. Some window plants such as Fenestraria species and some Haworthia species such as Haworthia tesselata and Haworthia truncata are examples of xerophytes. and Bulbine mesembryanthemoides. Leaves function to store chemical energy and water and may become specialised organs serving other functions, such as tendrils of peas and other legumes, the protective spines of cacti and the insect traps in carnivorous plants such as Nepenthes and Sarracenia. Leaves are the fundamental structural units from which cones are constructed in gymnosperms and from which flowers are constructed in flowering plants; the internal organisation of most kinds of leaves has evolved to maximise exposure of the photosynthetic organelles, the chloroplasts, to light and to increase the absorption of carbon dioxide while at the same time controlling water loss. Their surfaces are waterproofed by the plant cuticle and gas exchange between the mesophyll cells and the atmosphere is controlled by minute openings called stomata which open or close to regulate the rate exchange of carbon dioxide and water vapour into
The Balkenkreuz is a straight-armed cross, the emblem of the Wehrmacht and its branches from 1935 until the end of World War II. It was used by the Heer and Kriegsmarine. German Balken means "beam, bar", so a literal translation of Balkenkreuz would be "beam cross" or "bar cross". Germany's Luftstreitkräfte first adopted the Balkenkreuz in mid-April 1918, used it from that time until World War I ended in November 1918; the IdFlieg directive of 20 March 1918 to all manufacturers states in the first sentence: "To improve the recognition of our aircraft, the following is ordered: ". In paragraph 2, the second sentence specifies: "This alteration is to be carried out by 15 April 1918." The closing sentence reads: "Order 41390 is to be speedily executed."Its use resumed, with new standardized dimensions, from the beginning of the Third Reich's Luftwaffe in 1935, as part of the new Wehrmacht unified German military forces founded in mid-March 1935. German armored fighting vehicles during the invasion of Poland used a plain white cross, but before the onset of Operation Weserübung, the black core cross with white "flanks" that the Luftwaffe used had become the basic German AFV national insignia, as used for the rest of the war.
The Luftwaffe would use two specifications for the Balkenkreuz: one with narrower white "flanks" on upper wing surfaces - before July 1939, it was used in all six regular positions on an airframe one with wider white "flanks" surrounding the same width central black cross beneath the wings and on the fuselage sides of German military aircraft during the war yearsLate in World War II it became common for the Balkenkreuz national insignia to be painted on without the black-color "core cross", using only the quartet of right-angled "flanks" for its form to reduce its visibility - this could be done in either white or black, with both the narrow and wide-flank forms of the cross. The Iron Cross used by today's German Bundeswehr unified defense forces inherits the four white, or lighter-colored, "flanks" of the older Balkenkreuz that do not "cap" the ends of the cross in either case, but with the "flanks" following the flared arms of the earlier German Empire's cross pattée instead from the 1916-March 1918 era
A trefoil arch — or three-foiled cusped arch — is an arch incorporating the shape or outline of a trefoil — three overlapping rings. It has been used for its symbolic significance in Christian architecture
Hazard symbols or warning symbols are recognisable symbols designed to warn about hazardous or dangerous materials, locations, or objects, including electric currents and radioactivity. The use of hazard symbols is regulated by law and directed by standards organisations. Hazard symbols may appear with different colors, backgrounds and supplemental information in order to specify the type of hazard and the level of threat. Warning symbols are used in many places in lieu of or addition to written warnings as they are recognized and more understood. On roadside warning signs, an exclamation mark is used to draw attention to a generic warning of danger and the unexpected. In Europe, this type of sign is used if there are no more-specific signs to denote a particular hazard; when used for traffic signs, it is accompanied by a supplementary sign describing the hazard mounted under the exclamation mark. This symbol has been more adopted for generic use in many other contexts not associated with road traffic.
It appears on hazardous equipment or in instruction manuals to draw attention to a precaution, when a more-specific warning symbol is not available. The skull-and-crossbones symbol, consisting of a human skull and two bones crossed together behind the skull, is today used as a warning of danger of death in regard to poisonous substances; the symbol, or some variation thereof with the bones below the skull, was featured on the Jolly Roger, the traditional flag of European and American seagoing pirates. It is part of the Canadian WHMIS home symbols placed on containers to warn that the contents are poisonous. In the United States, due to concerns that the skull-and-crossbones symbol's association with pirates might encourage children to play with toxic materials, the Mr. Yuk symbol is used to denote poison; the international radiation symbol first appeared in 1946, at the University of California, Berkeley Radiation Laboratory. At the time, it was rendered as magenta, was set on a blue background.
The original version used in America is magenta against a yellow background, it is drawn with a central circle of radius R, an internal radius of 1.5R and an external radius of 5R for the blades, which are separated from each other by 60°. The trefoil is black in the international version, used in America; the sign is referred to as a radioactivity warning sign, but it is a warning sign of ionizing radiation. Ionizing radiation is a much broader category than radioactivity alone, as many non-radioactive sources emit dangerous levels of ionizing radiation; this includes x-ray apparatus, radiotherapy linear accelerators, particle accelerators. Non-ionizing radiation can reach dangerous levels, but this warning sign is different from the trefoil ionizing radiation warning symbol. On February 15, 2007, two groups—the International Atomic Energy Agency and the International Organization for Standardization —jointly announced the adoption of a new ionizing radiation warning symbol to supplement the traditional trefoil symbol.
The new symbol, to be used on sealed radiation sources, is aimed at alerting anyone, anywhere to the danger of being close to a strong source of ionizing radiation. It depicts, on a red background, a black trefoil with waves of radiation streaming from it, along with a black skull and crossbones, a running figure with an arrow pointing away from the scene; the radiating trefoil suggests the presence of radiation, while the red background and the skull and crossbones warn of the danger. The figure running away from the scene is meant to suggest taking action to avoid the labeled material; the new symbol is not intended to be visible, but rather to appear on internal components of devices that house radiation sources so that if anybody attempts to disassemble such devices they will see an explicit warning not to proceed any further. The biohazard symbol is used in the labeling of biological materials that carry a significant health risk, including viral samples and used hypodermic needles; the biohazard symbol was developed by the Dow Chemical Company in 1966 for their containment products.
According to Charles Baldwin, an environmental-health engineer who contributed to its development: "We wanted something, memorable but meaningless, so we could educate people as to what it means." In an article in Science in 1967, the symbol was presented as the new standard for all biological hazards. The article explained that over 40 symbols were drawn up by Dow artists, all of the symbols investigated had to meet a number of criteria: " striking in form in order to draw immediate attention; the chosen scored the best on nationwide testing for memorability. All parts of the biohazard sign can be drawn with straightedge; the basic outline of the symbol is a plain trefoil, three circles overlapping each other like in a triple Venn diagram with the overlapping parts erased. The diameter of the overlapping part is equal to half the radius of the three circles. Three inner circles are drawn in with 2⁄3 radius of the original circles so that it is tangent to the
The Axis powers known as "Rome–Berlin–Tokyo Axis", were the nations that fought in World War II against the Allies. The Axis powers agreed on their opposition to the Allies, but did not coordinate their activity; the Axis grew out of the diplomatic efforts of Germany and Japan to secure their own specific expansionist interests in the mid-1930s. The first step was the treaty signed by Germany and Italy in October 1936. Benito Mussolini declared on 1 November that all other European countries would from on rotate on the Rome–Berlin axis, thus creating the term "Axis"; the simultaneous second step was the signing in November 1936 of the Anti-Comintern Pact, an anti-communist treaty between Germany and Japan. Italy joined the Pact in 1937; the "Rome–Berlin Axis" became a military alliance in 1939 under the so-called "Pact of Steel", with the Tripartite Pact of 1940 leading to the integration of the military aims of Germany and Japan. At its zenith during World War II, the Axis presided over territories that occupied large parts of Europe, North Africa, East Asia.
There were no three-way summit meetings and cooperation and coordination was minimal, with more between Germany and Italy. The war ended in 1945 with the dissolution of their alliance; as in the case of the Allies, membership of the Axis was fluid, with some nations switching sides or changing their degree of military involvement over the course of the war. The term "axis" was first applied to the Italo-German relationship by the Italian prime minister Benito Mussolini in September 1923, when he wrote in the preface to Roberto Suster's Germania Repubblica that "there is no doubt that in this moment the axis of European history passes through Berlin". At the time, he was seeking an alliance with the Weimar Republic against Yugoslavia and France in the dispute over the Free State of Fiume; the term was used by Hungary's prime minister Gyula Gömbös when advocating an alliance of Hungary with Germany and Italy in the early 1930s. Gömbös' efforts did affect the Italo-Hungarian Rome Protocols, but his sudden death in 1936 while negotiating with Germany in Munich and the arrival of Kálmán Darányi, his successor, ended Hungary's involvement in pursuing a trilateral axis.
Contentious negotiations between the Italian foreign minister, Galeazzo Ciano, the German ambassador, Ulrich von Hassell, resulted in a Nineteen-Point Protocol, signed by Ciano and his German counterpart, Konstantin von Neurath, in 1936. When Mussolini publicly announced the signing on 1 November, he proclaimed the creation of a Rome–Berlin axis. Italy under Duce Benito Mussolini had pursued a strategic alliance of Italy with Germany against France since the early 1920s. Prior to becoming head of government in Italy as leader of the Italian Fascist movement, Mussolini had advocated alliance with defeated Germany after the Paris Peace Conference of 1919 settled World War I, he believed. In early 1923, as a goodwill gesture to Germany, Italy secretly delivered weapons for the German Army, which had faced major disarmament under the provisions of the Treaty of Versailles. In September 1923, Mussolini offered German Chancellor Gustav Stresemann a "common policy": he sought German military support against potential French military intervention over Italy's diplomatic dispute with Yugoslavia over Fiume, should an Italian seizure of Fiume result in war between Italy and Yugoslavia.
The German ambassador to Italy in 1924 reported that Mussolini saw a nationalist Germany as an essential ally for Italy against France, hoped to tap into the desire within the German army and the German political right for a war of revenge against France. During the Weimar Republic, the German government did not respect the Treaty of Versailles that it had been pressured to sign, various government figures at the time rejected Germany's post-Versailles borders. General Hans von Seeckt supported an alliance between Germany and the Soviet Union to invade and partition Poland between them and restore the German-Russian border of 1914. Gustav Streseman as German foreign minister in 1925 declared that the reincorporation of territories lost to Poland and Danzig in the Treaty of Versailles was a major task of German foreign policy; the Reichswehr Ministry memorandum of 1926 declared its intention to seek the reincorporation of German territory lost to Poland as its first priority, to be followed by the return of the Saar territory, the annexation of Austria, remilitarization of the Rhineland.
Since the 1920s Italy had identified the year 1935 as a crucial date for preparing for a war against France, as 1935 was the year when Germany's obligations under the Treaty of Versailles were scheduled to expire. Meetings took place in Berlin in 1924 between Italian General Luigi Capello and prominent figures in the German military, such as von Seeckt and Erich Ludendorff, over military collaboration between Germany and Italy; the discussions concluded that Germans still wanted a war of revenge against France but were short on weapons and hoped that Italy could assist Germany. However at this time Mussolini stressed one important condition that Italy must pursue in an alliance with Germany: that Italy "must... tow them, not be towed by them". Italian foreign minister Dino Grandi in the early 1930s stressed the importance of "decisive weight", involving Italy's relations between France and Germany, in which he recognized that Italy was not yet a major power, but perceived that Italy did have
Late Middle Ages
The Late Middle Ages or Late Medieval Period was the period of European history lasting from 1250 to 1500 AD. The Late Middle Ages followed the High Middle Ages and preceded the onset of the early modern period. Around 1300, centuries of prosperity and growth in Europe came to a halt. A series of famines and plagues, including the Great Famine of 1315–1317 and the Black Death, reduced the population to around half of what it was before the calamities. Along with depopulation came social unrest and endemic warfare. France and England experienced serious peasant uprisings, such as the Jacquerie and the Peasants' Revolt, as well as over a century of intermittent conflict, the Hundred Years' War. To add to the many problems of the period, the unity of the Catholic Church was temporarily shattered by the Western Schism. Collectively, those events are sometimes called the Crisis of the Late Middle Ages. Despite the crises, the 14th century was a time of great progress in the arts and sciences. Following a renewed interest in ancient Greek and Roman texts that took root in the High Middle Ages, the Italian Renaissance began.
The absorption of Latin texts had started before the Renaissance of the 12th century through contact with Arabs during the Crusades, but the availability of important Greek texts accelerated with the Capture of Constantinople by the Ottoman Turks, when many Byzantine scholars had to seek refuge in the West Italy. Combined with this influx of classical ideas was the invention of printing, which facilitated dissemination of the printed word and democratized learning; those two things would lead to the Protestant Reformation. Toward the end of the period, the Age of Discovery began; the expansion of the Ottoman Empire cut off trading possibilities with the East. Europeans were forced to seek new trading routes, leading to the Spanish expedition under Christopher Columbus to the Americas in 1492 and Vasco da Gama’s voyage to Africa and India in 1498, their discoveries strengthened the power of European nations. The changes brought about by these developments have led many scholars to view this period as the end of the Middle Ages and the beginning of modern history and of early modern Europe.
However, the division is somewhat artificial, since ancient learning was never absent from European society. As a result, there was developmental continuity between the modern age; some historians in Italy, prefer not to speak of the Late Middle Ages at all but rather see the high period of the Middle Ages transitioning to the Renaissance and the modern era. The term "Late Middle Ages" refers to one of the three periods of the Middle Ages, along with the Early Middle Ages and the High Middle Ages. Leonardo Bruni was the first historian to use tripartite periodization in his History of the Florentine People. Flavio Biondo used a similar framework in Decades of History from the Deterioration of the Roman Empire. Tripartite periodization became standard after the German historian Christoph Cellarius published Universal History Divided into an Ancient and New Period. For 18th-century historians studying the 14th and 15th centuries, the central theme was the Renaissance, with its rediscovery of ancient learning and the emergence of an individual spirit.
The heart of this rediscovery lies in Italy, where, in the words of Jacob Burckhardt: "Man became a spiritual individual and recognized himself as such". This proposition was challenged, it was argued that the 12th century was a period of greater cultural achievement; as economic and demographic methods were applied to the study of history, the trend was to see the late Middle Ages as a period of recession and crisis. Belgian historian Henri Pirenne continued the subdivision of Early and Late Middle Ages in the years around World War I, yet it was his Dutch colleague, Johan Huizinga, responsible for popularising the pessimistic view of the Late Middle Ages, with his book The Autumn of the Middle Ages. To Huizinga, whose research focused on France and the Low Countries rather than Italy and decline were the main themes, not rebirth. Modern historiography on the period has reached a consensus between the two extremes of innovation and crisis, it is now acknowledged that conditions were vastly different north and south of the Alps, the term "Late Middle Ages" is avoided within Italian historiography.
The term "Renaissance" is still considered useful for describing certain intellectual, cultural, or artistic developments, but not as the defining feature of an entire European historical epoch. The period from the early 14th century up until – and sometimes including – the 16th century, is rather seen as characterized by other trends: demographic and economic decline followed by recovery, the end of western religious unity and the subsequent emergence of the nation state, the expansion of European influence onto the rest of the world; the limits of Christian Europe were still being defined in the 15th centuries. While the Grand Duchy of Moscow was beginning to repel the Mongols, the Iberian kingdoms completed the Reconquista of the peninsula and turned their attention outwards, the Balkans fell under the dominance of the Ottoman Empire. Meanwhile, the remaining nations of the continent were locked in constant international or internal conflict; the situation led to the consolidation of central authority and the emergence of the nation state.
The financial demands of war necessitated higher levels of taxation, resulting in the emergence of representative bodies – most notably the English Parliament. The growth of secular authority was further aided by t
Clover or trefoil are common names for plants of the genus Trifolium, consisting of about 300 species of flowering plants in the legume or pea family Fabaceae. The genus has a cosmopolitan distribution with highest diversity in the temperate Northern Hemisphere, but many species occur in South America and Africa, including at high altitudes on mountains in the tropics, they are small biennial, or short-lived perennial herbaceous plants. Clover can be evergreen; the leaves are trifoliate, cinquefoil, or septfoil), with stipules adnate to the leaf-stalk, heads or dense spikes of small red, white, or yellow flowers. Other related genera called clovers include Melilotus and Medicago. Several species of clover are extensively cultivated as fodder plants; the most cultivated clovers are white clover, Trifolium repens, red clover, Trifolium pratense. Clover, either sown alone or in mixture with ryegrass, has for a long time formed a staple crop for silaging, for several reasons: it grows shooting up again after repeated mowings.
In many areas on acidic soil, clover is short-lived because of a combination of insect pests and nutrient balance. When crop rotations are managed so that clover does not recur at intervals shorter than eight years, it grows with much of its pristine vigor. Clovers are most efficiently pollinated by bumblebees, which have declined as a result of agricultural intensification. Honeybees can pollinate clover, beekeepers are in heavy demand from farmers with clover pastures. Farmers reap the benefits of increased reseeding that occurs with increased bee activity, which means that future clover yields remain abundant. Beekeepers benefit from the clover bloom. Trifolium repens, white or Dutch clover, is a perennial abundant in good pastures; the flowers are pinkish, becoming brown and deflexed as the corolla fades. Trifolium hybridum, alsike or Swedish clover, is a perennial, introduced early in the 19th century and has now become naturalized in Britain; the flowers are white or rosy, resemble those of Trifolium repens.
Trifolium medium, meadow or zigzag clover, a perennial with straggling flexuous stems and rose-purple flowers, has potential for interbreeding with T. pratense to produce perennial crop plants. Other species are: hare's - foot trefoil. Shamrock, the traditional Irish symbol, which according to legend was coined by Saint Patrick for the Holy Trinity, is associated with clover, although alternatively sometimes with the various species within the genus Oxalis, which are trifoliate. Clovers have four leaflets, instead of the usual three; these four-leaf clovers, like other rarities, are considered lucky. Clovers can have five, six, or more leaflets, but these are rarer still; the record for most leaflets is 56, set on 10 May 2009. This beat the "21-leaf clover", a record set in June 2008 by the same discoverer, who had held the prior Guinness World Record of 18. A common idiom is "to be in clover", meaning to live a carefree life of ease, comfort, or prosperity; the cloverleaf interchange is named for the resemblance to the leaflets of a clover when viewed from the air.
The first extensive classification of Trifolium was done by Zohary and Heller in 1984. They divided the genus into eight sections: Lotoidea, Mistyllus, Chronosemium, Trifolium and Involucrarium, with Lotoidea placed most basally. Within this classification system, Trifolium repens falls within section Lotoidea, the largest and least heterogeneous section. Lotoidea contains species from America and Eurasia, considered a clade because of their inflorescence shape, floral structure, legume that protrudes from the calyx. However, these traits are not unique to the section, are shared with many other species in other sections. Zohary and Heller argued that the presence of these traits in other sections proved the basal position of Lotoidea, because they were ancestral. Aside from considering this section basal, they did no propose relationships between other sections. Since molecular data has both questioned and confirmed the proposed phylogeny from Zohary and Heller. A genus-wide molecular study has since proposed a new classification system, made up of two subgenera and Trifolium.
This recent reclassification further divides subgenus Trifolium into eight sections. The molecular data supports the monophyletic nature of three sections proposed by Zohary and Heller, but not of Lotoidea. Other molecular studies, although smaller, support the need to reorganize Lotoidea; the genus Trifolium has 245 recognized