Etymology.

The Republic of Kenya is named after Mount Kenya. The earliest recorded version of the modern name was written by German explorer Johann Ludwig Krapf in the 19th century. While travelling with a Kamba caravan led by the legendary long-distance trader Chief Kivoi, Krapf spotted the mountain peak and asked what it was called. Kivoi told him ""Kĩ-Nyaa"" or ""Kĩĩma- Kĩĩnyaa"", probably because the pattern of black rock and white snow on its peaks reminded him of the feathers of the male

History.

Human Prehistory.

Fossils found in Kenya have shown that primates inhabited the area for more than 20 million years. Recent findings near Lake Turkana indicate that hominids such as "Homo habilis" (1.8 to 2.5 million years ago) and "Homo erectus" (1.9 million to 350,000 years ago) are possible direct ancestors of modern "Homo sapiens", and lived in Kenya in the Pleistocene epoch.  During excavations at Lake Turkana in 1984, paleoanthropologist Richard Leakey, assisted by Kamoya Kimeu, discovered the Turkana Boy, a 1.6-million-year-old "Homo erectus" fossil. Previous research on early hominids is particularly identified with Mary Leakey and Louis Leakey, who were responsible

Neolithic.

The first inhabitants of present-day Kenya were hunter-gatherer groups, akin to the modern Khoisan speakers. These people were later largely replaced by agropastoralist Cushitic (ancestral to Kenya's Cushitic speakers) from the Horn of Africa. During the early Holocene, the regional climate shifted from dry to wetter conditions, providing an opportunity for the development of cultural traditions such as agriculture and herding, in a more favourable environment.  Around 500 BC, Nilotic-speaking pastoralists (ancestral to Kenya's Nilotic speakers) started migrating

Swahili trade period.

The Kenyan coast had served host to communities of ironworkers and Bantu subsistence farmers, hunters, and fishers who supported the economy with agriculture, fishing, metal production, and trade with foreign countries. These communities formed the earliest city-states in the region, which were collectively known as Azania.  By the 1st century CE, many of the city-states such as Mombasa, Malindi, and Zanzibar began to establish trading relations with Arabs. This led to increased economic growth of the Swahili states, the introduction of Islam, Arabic influences on the Swahili Bantu language, cultural diffusion, as well as the Swahili city-states becoming members of a larger trade network. Many historians had long believed that the

Early Portuguese colonization.

The Swahili built Mombasa into a major port city and established trade links with other nearby city-states, as well as commercial centres in Persia, Arabia, and even India. By the 15th-century, Portuguese voyager Duarte Barbosa claimed that "Mombasa is a place of great traffic and has a good harbour in which there are always moored small craft of many kinds and also great ships, both of which are bound from Sofala and others which come from Cambay and Melinde and others which sail to the island of Zanzibar."  Later on in the 17th century, the Swahili coast was conquered and came under direct rule of

British Kenya (1888–1962).

The colonial history of Kenya dates from the establishment of a German protectorate over the Sultan of Zanzibar's coastal possessions in 1885, followed by the arrival of the Imperial British East Africa Company in 1888. Imperial rivalry was prevented when Germany handed its coastal holdings to Britain in 1890. This was followed by the building of the Uganda Railway passing through the country.  The building of the railway was resisted by some ethnic groups—notably the Nandi, led by "Orkoiyot" Koitalel Arap Samoei for ten years from 1890 to 1900—however the British eventually built the railway. The "Nandi" were the first ethnic group to be put in a

Mau Mau Uprising.

From October 1952 to December 1959, Kenya was in a state of emergency arising from the Mau Mau rebellion against British rule. The Mau Mau, also known as the Kenya Land and Freedom Army, were primarily members of the Kikuyu ethnic group.  The governor requested and obtained British and African troops, including the King's African Rifles. The British began counter-insurgency operations. In May 1953, General Sir George Erskine took charge as commander-in-chief of the colony's armed forces, with the personal backing of Winston Churchill.  The capture of Waruhiu Itote (nom de guerre ""General China"") on 15 January 1954 and the subsequent interrogation led to a better understanding of the Mau Mau command structure

Somalis of Kenya referendum, 1962.

Before Kenya got its independence, Somali ethnic people in the present-day Kenya in the areas of Northern Frontier Districts petitioned Her Majesty's Government not to be included in Kenya. The colonial government decided

Independence.

The first direct elections for native Kenyans to the Legislative Council took place in 1957.  Despite British hopes of handing power to "moderate" local rivals, it was the Kenya African National Union (KANU) of Jomo Kenyatta that formed a government. The Colony of Kenya and the Protectorate of Kenya each came to an end on 12 December 1963, with independence being conferred on all of Kenya. The United Kingdom ceded sovereignty over the Colony of Kenya. The Sultan of Zanzibar agreed that simultaneous with independence for

The first president of Kenya.

On 12 December 1964, the Republic of Kenya was proclaimed, and Jomo Kenyatta became Kenya's first president. Under Kenyatta, corruption became widespread throughout the government, civil service, and business community. Kenyatta and his family were tied up with this corruption as they enriched themselves through

Moi era.

Following Kenyatta's death in 1978, Daniel arap Moi became president. He retained the presidency, running unopposed in elections held in 1979, 1983 (snap elections), and 1988, all of which were held under the single-party constitution. The 1983 elections were held a year early, and were a direct result of a failed military coup on 2 August 1982.  The 1982 coup was masterminded by a low-ranking Air Force serviceman, Senior Private Hezekiah Ochuka, and was staged mainly by enlisted men of the Air Force. It was quickly suppressed by forces

Transition to multiparty democracy.

In 1991, Kenya transitioned to a multiparty political system after 26 years of single-party rule. On 28 October 1992, president Moi dissolved parliament, five months before the end of his term. As a result, preparations began for all elective seats in parliament as well as the president. The elections were scheduled to take place on 7 December 1992, but delays led to its postponement to 29 December the same year. Apart from KANU, the ruling party, other parties represented in the elections included FORD Kenya and FORD Asili. This election was marked by large-scale intimidation of opponents, as well as harassment of election officials. It resulted in an economic crisis propagated by ethnic violence as the president was accused of rigging electoral results to retain power. This election was a turning point for Kenya as it signified the beginning of the end of Moi's

President Kibaki and the road to a new constitution.

Moi's plan to be replaced by Uhuru Kenyatta failed, and Mwai Kibaki, running for the opposition coalition "National Rainbow Coalition" (NARC), was elected president. David Anderson (2003) reports the elections were judged free and fair by local and international observers, and seemed to mark a turning point in Kenya's democratic evolution.  In 2005, Kenyans rejected a plan to replace the 1963 independence constitution with a new one. As a result, the elections of 2007 took place following the procedure set by the old constitution. Kibaki was re-elected

Devolution of government and separation of powers.

Following the passage of the new constitution, Kenya became a presidential representative democratic republic, whereby the President of Kenya is both head of state and head of government, and of a multi-party system. The new constitution also states that executive powers are exercised by the executive branch of government, headed by the president, who chairs the cabinet that is composed of people chosen from outside parliament. Legislative power is vested exclusively in Parliament. The judiciary is independent of the executive and the legislature. Mwai Kibaki became the first president to serve under this new constitution while Uhuru Kenyatta became the first president elected under this constitution.  In 2011, Kenya began sending troops to Somalia to fight the Islamic terror group Al-Shabaab. In mid-2011, two consecutive missed rainy seasons precipitated the worst drought in East Africa seen in 60 years. The northwestern Turkana region was especially affected, with local schools shut down as a result. The

Geography and climate.

At, Kenya is the world's forty-seventh largest country (after Madagascar). It lies between latitudes 5°N and 5°S, and longitudes 34° and 42°E. From the coast on the Indian Ocean, the low plains rise to central highlands. The highlands are bisected by the Great Rift Valley, with a fertile plateau lying to the east.  The Kenyan Highlands are one of the most successful agricultural production regions in Africa. The highlands are the site of the highest point in Kenya and the second highest peak on the continent: Mount Kenya, which reaches a height of and is the site of glaciers. Mount Kilimanjaro () can be seen from Kenya to the south of the Tanzanian border.

Climate.

Kenya's climate varies from tropical along the coast to temperate inland to arid in the north and northeast parts of the country. The area receives a great deal of sunshine every month. It is usually cool at night and early in the morning inland at

Wildlife.

Kenya has considerable land area devoted to wildlife habitats, including the Masai Mara, where blue wildebeest and other bovids participate in a large-scale. More than 1 million wildebeest and 200,000 zebras participate in the migration across the Mara River.  The "Big Five" game animals of Africa, that is the lion, leopard, buffalo, rhinoceros, and elephant, can be found in Kenya

Government and politics.

Kenya is a presidential representative democratic republic with a multi-party system. The president is both the head of state and head of government. Executive power is exercised by the government. Legislative power is vested in both the government and the National Assembly and the Senate. The Judiciary is independent of the executive and the legislature. There has been growing concern, especially during former president Daniel arap Moi's tenure, that the executive was increasingly meddling with the affairs of the judiciary.  Kenya has high levels of corruption according to Transparency International's Corruption Perceptions Index (CPI), a metric which attempts to gauge the prevalence of public-sector corruption in various countries. In 2019, the nation placed 137th out of 180 countries in the index, with a score of 28 out of 100. However, there are several rather significant developments with regards to curbing corruption from the Kenyan government, for instance, the establishment of a new and independent Ethics and Anti-Corruption Commission (EACC). Following general elections held in 1997, the Constitution of Kenya Review Act, designed to pave the way for more comprehensive amendments to the Kenyan constitution, was passed by the national parliament.  In December 2002, Kenya held democratic and open elections, which were judged free and fair by most international observers. The 2002 elections marked an important turning point in Kenya's democratic evolution in that power was transferred peacefully from the Kenya African National Union (KANU), which had ruled the country since independence, to the National Rainbow Coalition (NARC), a coalition of political parties.  Under the presidency of Mwai Kibaki, the new ruling coalition promised to focus its efforts on generating economic growth, combating corruption, improving education, and rewriting its constitution. A few of these promises have been met. There is free primary education. In 2007, the government issued a statement declaring that from 2008, secondary education would be heavily subsidised, with the government footing all tuition fees.

2013 elections and new government.

Under the new constitution and with President Kibaki prohibited by term limits from running for a third term, Deputy Prime Minister Uhuru Kenyatta ran for office. He won with 50.51% of the vote in March 2013.  In December 2014, President Uhuru Kenyatta signed a Security Laws Amendment Bill, which

Foreign relations.

Kenya has close ties with its fellow Swahili-speaking neighbours in the African Great Lakes region. Relations with Uganda and Tanzania are generally strong, as the three nations work toward economic and social integration through common membership in the East African Community.  Relations with Somalia have historically been tense, although there has been some military co-ordination against Islamist insurgents. Kenya has good relations with the United Kingdom. Kenya is one of the most pro-American nations in Africa, and

Armed forces.

The Kenya Defence Forces are the armed forces of the Republic of Kenya. The Kenya Army, Kenya Navy, and Kenya Air Force compose the National Defence Forces. The current Kenya Defence Forces were established, and its composition laid out, in Article 241 of the 2010 Constitution of Kenya; the KDF is governed by the Kenya Defence Forces Act of 2012. The President of Kenya is the commander-in-chief of all the armed forces.  The armed forces are regularly deployed in peacekeeping missions around the world. Further, in the aftermath of the national elections of December 2007 and the violence

Administrative divisions.

Kenya is divided into 47 semi-autonomous counties that are headed by governors. These 47 counties form the first-order divisions of Kenya.  The smallest administrative units in Kenya are called locations. Locations often coincide with electoral wards. Locations are usually named after their central villages/towns.

Human rights.

Homosexual acts are illegal in Kenya and punishable by up to 14 years in prison, though the state often turns a blind eye to prosecuting gay people. According to a 2013 survey by the Pew Research Center, 90% of Kenyans believe that homosexuality should not be accepted by society. While addressing a joint press conference together with President Barack Obama in 2015, President Kenyatta declined to

Economy.

Kenya's macroeconomic outlook has steadily posted robust growth over the past few decades, mostly from road and rail infrastructure projects. However, much of this growth has come from cash flows diverted from ordinary Kenyan pockets at the microeconomic level through targeted monetary and fiscal measures coupled with poor management, corruption, massive theft of public funds, overlegislation, and an ineffective judiciary, resulting in diminished incomes in ordinary households and small businesses, unemployment, underemployment, and general discontent across multiple sectors. Kenya ranks poorly on the Fragile States Index at number 25 out of 178 countries, ranked in 2019, and is placed in the ALERT category. In 2014, the country's macroeconomic indicators were re-based, causing the GDP to shift upwards to low-middle-income country status.  Kenya has a Human Development Index (HDI) of 0.555 (medium), ranked 145 out of 186 in the world., 17.7% of Kenyans lived on less than $1.25 a day. In 2017, Kenya ranked 92nd in the World Bank ease of doing business rating from 113rd in 2016 (of 190 countries). The important agricultural sector is one of the least developed and largely inefficient, employing 75% of the workforce compared to less than 3% in the food secure developed countries. Kenya is usually classified as a frontier market or occasionally an emerging market, but it is not one of the least developed countries.  The economy has seen much expansion, seen by strong performance in tourism, higher education, and telecommunications, and acceptable post-drought results in agriculture, especially the vital tea sector. Kenya's economy grew by more than 7% in 2007, and its foreign debt was greatly reduced. This changed immediately after the disputed presidential election of December 2007, following the chaos which engulfed the country.  Telecommunications and financial activity over the last decade now comprise 62% of GDP. 22% of GDP still comes from the unreliable agricultural sector which employs 75% of the labour force (a consistent characteristic of under-developed economies that have not attained food security—an important catalyst of economic growth). A small portion of the population relies on food aid. Industry and manufacturing is the smallest sector, accounting for 16% of GDP. The service, industry and manufacturing sectors only employ 25% of the labour force but contribute 75% of GDP. Kenya also exports textiles worth over $400 million under AGOA.  Privatisation of state corporations like the defunct Kenya Post and Telecommunications Company, which resulted in East Africa's most profitable company—Safaricom, has led to their revival because of massive private investment. , economic prospects are positive with 4–5% GDP growth expected, largely because of expansions in tourism, telecommunications, transport, construction, and a recovery in agriculture. The World Bank estimated growth of 4.3% in 2012.  In March 1996, the presidents of Kenya, Tanzania, and Uganda re-established the East African Community (EAC). The EAC's objectives include harmonising tariffs and customs regimes, free movement of people, and improving regional infrastructures. In March 2004, the three East African countries signed a Customs Union Agreement.  Kenya has a more developed financial services sector than its neighbours. The Nairobi Securities Exchange (NSE) is ranked 4th in Africa in terms of market capitalisation. The Kenyan banking system is supervised by the Central Bank of Kenya (CBK). As of late July 2004, the system consisted of 43 commercial banks (down from 48 in 2001) and several non-bank financial institutions including mortgage companies, four savings and loan associations, and several core foreign-exchange bureaus.

Demographics.

Kenya had a population of approximately 48 million people in January 2017. The country has a young population, with 73% of residents aged below 30 years because of rapid population growth, from 2.9 million to 40 million inhabitants over the last century.  Kenya's capital, Nairobi, is home to Kibera, one of the world's largest slums. The shantytown is believed to house between 170,000 and 1 million people. The UNHCR base in Dadaab in the north also currently houses around 500,000 people.

Ethnic groups.

Kenya has a diverse population that includes many of the major ethnoracial and linguistic groups found in Africa. There are an estimated 47 different communities, with Bantus (60%) and Nilotes (30%) constituting the majority of local residents. Cushitic groups also form a small ethnic minority, as do Arabs, Indians, and Europeans.

Languages.

Kenya's various ethnic groups typically speak their mother tongues within their own communities. The two official languages, English and Swahili, are used in varying degrees of fluency for communication with other populations. English is widely spoken in commerce, schooling, and government. Peri-urban and rural dwellers are less multilingual, with many in rural areas speaking only their native languages.  British English is primarily used in Kenya. Additionally, a distinct local dialect, Kenyan English, is used by some communities and individuals

Religion.

The majority of Kenyans are Christian (85.5%), of whom 53.9% are Protestant and 20.6% are Roman Catholic. The Presbyterian Church of East Africa has 3 million followers in Kenya and surrounding countries. There are smaller conservative Reformed churches, the Africa Evangelical Presbyterian Church, the Independent Presbyterian Church in Kenya, and the Reformed Church of East Africa. Orthodox Christianity counts 621,200 adherents. Kenya has by far the highest number of Quakers of any country in the world, with

Health.

Private health facilities are diverse, highly dynamic, and difficult to classify, unlike public health facilities, which are easily grouped in classes that consist of community-based (level I) services, run by community health workers; dispensaries (level II facilities) run by nurses; health centers (level III facilities), run by clinical officers; sub-county hospitals (level IV facilities), which may be run by a clinical officer or a medical officer; county hospitals (level V facilities), which may be run by a medical officer or a medical practitioner; and national referral hospitals (level VI facilities), which are run by fully qualified medical practitioners.  Nurses are by far the largest group of front-line health care providers in all sectors, followed by clinical officers, medical officers, and medical practitioners. According to the Kenya National Bureau of Statistics, in 2011 there were 65,000 qualified nurses registered in the country, 8,600 clinical officers, and 7,000 doctors, for the population of 43 million

Women.

The total fertility rate in Kenya was estimated to be 4.49 children per woman in 2012. According to a 2008–09 survey by the Kenyan government, the total fertility rate was 4.6% and the contraception usage rate among married women was 46%. Maternal mortality is high, partly because of female genital mutilation, with about 27% of women having undergone

Education.

Children attend nursery school, or kindergarten in the private sector until they are five years old. This lasts one to three years (KG1, KG2 and KG3) and is financed privately because there has been no government policy on pre-schooling until recently.  Basic formal education starts at age six and lasts 12 years, consisting of eight years in primary school and four in high school or secondary. Primary school is free in public schools and those attending can join a vocational youth/village polytechnic, or make their own arrangements

Culture.

The culture of Kenya consists of multiple traditions. Kenya has no single prominent culture that identifies it. It instead consists of the various cultures of the country's different communities.  Notable populations include the Swahili on the coast, several other Bantu communities in the central and western regions, and Nilotic communities in the northwest. The Maasai culture is well known to tourism, despite constituting a relatively small part of Kenya's population. They are renowned for their elaborate upper-body adornment and jewellery.  Additionally, Kenya has an extensive music, television, and theatre scene.

Media.

Kenya has a number of media outlets that broadcast domestically and globally. They cover news, business, sports, and

Literature.

Ngũgĩ wa Thiong'o is one of the best known writers in Kenya. His novel, "Weep Not, Child", is an illustration of life in Kenya during the British occupation. The story details the effects of the Mau Mau on the lives of Kenyans. Its combination of themes—colonialism, education, and love—helped to make it one of the best-known novels in Africa.

Music.

Kenya has a diverse assortment of popular music forms, in addition to multiple types of folk music based on the variety of over 40 regional languages.  Drums are the most dominant instrument in popular Kenyan music. Drum beats are very complex and include both native rhythms and imported ones, especially the Congolese cavacha rhythm. Popular Kenyan music usually involves the interplay of multiple parts, and more recently, showy guitar solos as well. There are also a number of local hip-hop artists, including Jua Cali; Afro-pop bands such as Sauti Sol; and musicians who play local genres like Benga, such as Akothee.  Lyrics are most often in Kiswahili or English. There is also some emerging aspect of Lingala borrowed from Congolese musicians. Lyrics are also

Sports.

Kenya is active in several sports, among them cricket, rallying, football, rugby, field hockey, and boxing. The country is known chiefly for its dominance in middle-distance and long-distance athletics, having consistently produced Olympic and Commonwealth Games champions in various distance events, especially in 800 m, 1,500 m, 3,000 m steeplechase, 5,000 m, 10,000 m, and the marathon. Kenyan athletes (particularly Kalenjin), continue to dominate the world of distance running, although competition from Morocco and Ethiopia has reduced this supremacy. Kenya's best-known athletes include the four-time women's Boston Marathon winner and two-time world champion Catherine Ndereba, 800m world record holder David Rudisha, former marathon world record-holder Paul Tergat, and John Ngugi.  Kenya won several medals during the Beijing Olympics: six gold, four silver, and four bronze, making it Africa's most successful nation in the 2008 Olympics. New athletes gained attention, such as Pamela Jelimo, the women's 800m gold medalist who went on to win the IAAF Golden League jackpot, and Samuel Wanjiru, who won the men's marathon. Retired Olympic and Commonwealth Games champion Kipchoge Keino helped usher in Kenya's ongoing distance dynasty in the 1970s and was followed by Commonwealth Champion Henry Rono's spectacular string of world record performances. Lately, there has been controversy in Kenyan athletics circles, with the defection of a number of Kenyan athletes to represent other countries, chiefly Bahrain and Qatar. The Kenyan Ministry of Sports has tried to stop the defections, but they have continued anyway, with Bernard Lagat being the latest, choosing to represent the United States. Most of these defections occur because of economic or financial factors. Decisions by the Kenyan government to tax athletes' earnings may also

Cuisine.

Kenyans generally have three meals in a day—breakfast ("kiamsha kinywa"), lunch ("chakula cha mchana"), and supper ("chakula cha jioni" or simply "chajio"). In between, they have the 10-o'clock tea ("chai ya saa nne") and 4 p.m. tea ("chai ya saa kumi"). Breakfast is usually tea or porridge with bread, chapati, mahamri, boiled sweet potatoes, or yams. Githeri is a common lunchtime dish in many

Kenya (), officially the Republic of Kenya (), is a country in Africa with 47 semiautonomous counties governed by elected governors. At, Kenya is the world's 48th largest country by total area. With a population of more than 47.6 million people, Kenya is the 29th most populous country. Kenya's capital and largest city is Nairobi, while its oldest city and first capital is the coastal city of Mombasa. Kisumu City is the third largest city and also an inland port on Lake Victoria. Other important urban centres include Nakuru and Eldoret. As of 2020, Kenya is the third largest economy in sub-Saharan Africa after Nigeria and South Africa. Kenya is bordered by South Sudan to the northwest, Ethiopia to the north, Somalia to the east, Uganda to the west, Tanzania to the south, and the Indian Ocean to the southeast.

肯尼亚共和国(,英语:Republic of Kenya,,或) 通称肯尼亚,是位于东非,濒临印度洋,与索马里、埃塞俄比亚、南苏丹、乌干达、坦桑尼亚接壤,面积约58万平方公里。肯尼亚人口约5051万,一共有42个民族,分成班图、尼罗和库施特三大语系,官方语言是英语和斯瓦希里语。全国分为47个县市,首都为内罗毕。


Structure.

The liver is a reddish-brown, wedge-shaped organ with two lobes of unequal size and shape. A human liver normally weighs approximately and has a width of about. There is considerable size variation between individuals, with the standard reference range for men being and for women. It is both the heaviest internal organ and the largest gland in the human body. Located in the right upper quadrant of the abdominal cavity, it rests just below the diaphragm, to the right of the stomach and overlies the gallbladder.  The liver is connected to two large blood vessels: the hepatic artery and the portal vein. The hepatic artery carries oxygen-rich blood from the aorta via the celiac trunk, whereas the portal vein carries blood rich in digested nutrients from the entire gastrointestinal tract and also from the spleen and pancreas. These blood vessels subdivide into small capillaries known as liver sinusoids, which then lead to lobules.  Lobules are the functional units of the liver. Each lobule is made up of millions of hepatic cells (hepatocytes), which are the basic metabolic cells. The lobules are held together by a fine, dense, irregular, fibroelastic connective tissue layer extending from the fibrous capsule covering the entire liver known as Glisson's capsule. This extends into the structure of the liver by accompanying the blood vessels, ducts, and nerves at the hepatic hilum. The whole surface of the liver, except for the bare area, is covered in a serous coat derived from the peritoneum, and this firmly adheres to the inner Glisson's capsule.

Gross anatomy.

Terminology related to the liver often starts in "hepat-" from ἡπατο-, from the Greek word for liver.

Lobes.

The liver is grossly divided into two parts when viewed from above – a right and a left lobe - and four parts when viewed from below (left, right, caudate, and quadrate lobes).  The falciform ligament divides the liver into a left and right lobe. From below, the two additional lobes are located between the right and left lobes, one in front of the other. A line can be imagined

Surfaces.

On the diaphragmatic surface, apart from a triangular bare area where it connects to the diaphragm, the liver is covered by a thin, double-layered membrane, the peritoneum, that helps to reduce friction against other organs. This surface covers the convex shape of the two lobes where it accommodates the shape of the diaphragm. The peritoneum folds back on itself to form the falciform ligament and the right and left triangular

Impressions.

Several impressions on the surface of the liver accommodate the various adjacent structures and organs. Underneath the right lobe and to the right of the gallbladder fossa are two impressions, one behind the other and separated by a ridge. The one in front is a shallow colic impression, formed by the hepatic flexure and the one behind is a deeper renal impression accommodating part of the right kidney and part of the suprarenal gland.  The suprarenal impression is a small, triangular, depressed area on the liver. It is located close to the right of

Microscopic anatomy.

Microscopically, each liver lobe is seen to be made up of hepatic lobules. The lobules are roughly hexagonal and consist of plates of hepatocytes radiating from a central vein.The central vein joins to the hepatic vein to carry blood out from the liver. A distinctive component of a lobule is the portal triad, which can be found running along each of the lobule's corners. The portal triad, misleadingly named, consists of five structures: a branch of the hepatic artery, a branch of the hepatic portal vein, and a bile duct,

Functional anatomy.

The central area or hepatic hilum, includes the opening known as the porta hepatis which carries the common bile duct and common hepatic artery, and the opening for the portal vein. The duct, vein, and artery divide into left and right branches, and the areas of the liver supplied by these branches constitute the functional left and right lobes. The functional lobes are separated by the imaginary plane, Cantlie's line, joining the gallbladder fossa to the inferior vena cava. The

Couinaud classification system.

In the widely used Couinaud system, the functional lobes are further divided into a total of eight subsegments based on a transverse plane through the bifurcation of the main portal vein. The caudate lobe is a separate structure that receives blood flow from both the right- and left-sided vascular branches. The Couinaud classification divides the liver into eight functionally independent liver segments. Each segment has its own vascular inflow,

Gene and protein expression.

About 20,000 protein coding genes are expressed in human cells and 60% of these genes are expressed in a normal, adult liver. Over 400 genes are more specifically expressed in the liver, with some 150 genes highly specific for liver tissue. A large fraction of the corresponding liver specific proteins

Development.

Organogenesis, the development of the organs, takes place from the third to the eighth week during embryogenesis. The origins of the liver lie in both the ventral portion of the foregut endoderm (endoderm being one of the three embryonic germ layers) and the constituents of the adjacent septum transversum mesenchyme. In the human embryo, the hepatic diverticulum is the tube of endoderm that extends out from the foregut into the surrounding mesenchyme. The mesenchyme of septum transversum induces this endoderm to proliferate, to branch, and to form the glandular epithelium of the liver. A portion of the hepatic diverticulum (that region closest to the digestive tube) continues to function as the drainage duct of the liver, and a branch from this duct produces the gallbladder. Besides signals from the septum transversum mesenchyme, fibroblast growth factor from the developing heart also contributes to hepatic competence, along with retinoic acid emanating from the lateral plate mesoderm. The hepatic endodermal cells undergo a morphological transition from columnar to pseudostratified resulting in thickening into the early liver bud. Their expansion forms a population of the bipotential hepatoblasts. Hepatic stellate cells are derived from mesenchyme.  After migration of hepatoblasts into the septum transversum mesenchyme, the hepatic architecture begins to be established, with liver sinusoids and bile canaliculi appearing. The liver bud separates into the lobes. The left umbilical vein becomes the ductus venosus and the right vitelline vein becomes the portal vein. The expanding liver bud is colonized by hematopoietic cells. The bipotential hepatoblasts begin differentiating into biliary epithelial cells and hepatocytes. The biliary epithelial cells differentiate from hepatoblasts around portal veins, first producing a monolayer, and then a bilayer of cuboidal cells. In ductal plate, focal dilations emerge at points in the bilayer, become surrounded by portal mesenchyme, and undergo tubulogenesis into intrahepatic bile ducts. Hepatoblasts not adjacent to portal veins instead differentiate into hepatocytes and arrange into cords lined by sinudoidal epithelial cells and bile canaliculi. Once hepatoblasts are specified into hepatocytes and undergo further expansion, they begin acquiring the functions of a mature hepatocyte, and eventually mature hepatocytes appear as highly polarized epithelial cells with abundant glycogen accumulation. In the adult liver, hepatocytes are not equivalent, with position along the portocentrovenular axis within a liver lobule dictating expression of metabolic genes involved in drug metabolism, carbohydrate metabolism, ammonia detoxification, and bile production and secretion. WNT/β-catenin has now been identified to be playing a key role in this phenomenon.  At birth, the liver comprises roughly 4% of body weight and weighs on average about. Over the course of further development, it will increase to but will only take up 2.5–3.5% of body weight.

Functions.

The various functions of the liver are carried out by the liver cells or hepatocytes. The liver is thought to be responsible for up to 500 separate functions, usually in combination with other systems and organs. Currently, no artificial organ or device is capable of reproducing all the functions of the liver. Some functions can be carried out by liver dialysis, an experimental treatment for liver failure. The liver also accounts for about 20% of resting total body oxygen consumption.

Blood supply.

The liver receives a dual blood supply from the hepatic portal vein and hepatic arteries. The hepatic portal vein delivers around 75% of the liver's blood supply and carries venous blood drained from the spleen, gastrointestinal tract, and its associated organs. The hepatic arteries supply arterial blood to the liver, accounting for the remaining quarter of its blood flow.

Biliary flow.

The biliary tract is derived from the branches of the bile ducts. The biliary tract, also known as the biliary tree, is the path by which bile is secreted by the liver then transported to the first part of the small intestine, the duodenum. The bile produced in the liver is collected in bile canaliculi, small grooves between the faces of adjacent hepatocytes. The canaliculi radiate to the edge of the liver lobule, where they merge to form bile ducts. Within the liver, these

Synthesis.

The liver plays a major role in carbohydrate, protein, amino acid, and lipid metabolism. The liver performs several roles in carbohydrate metabolism: The liver synthesizes and stores around 100 g of glycogen via glycogenesis, the formation of glycogen from glucose. When needed, the liver releases glucose into the blood by performing glycogenolysis, the breakdown of glycogen into glucose. The liver is also responsible for gluconeogenesis, which is the synthesis of glucose from certain amino acids, lactate, or glycerol. Adipose and liver cells produce glycerol by breakdown of fat, which the liver uses for gluconeogenesis.  The liver is responsible for the mainstay of protein metabolism, synthesis as well as degradation. It is also responsible for a large part of amino acid synthesis. The liver plays a role in the production of clotting factors,

Breakdown.

The liver is responsible for the breakdown of insulin and other hormones. The liver breaks down bilirubin via glucuronidation, facilitating its excretion into bile. The liver is responsible for the breakdown and excretion of many waste products. It plays a key role in

Blood reservoir.

Because the liver is an expandable organ, large quantities of blood can be stored in its blood vessels. Its normal blood volume, including both that in the hepatic veins and that in the hepatic sinuses, is about 450 milliliters, or almost 10 percent of the body's total blood volume. When high

Lymph production.

Because the pores in the hepatic sinusoids are very permeable and allow ready passage of both fluid and proteins into the spaces of disse, the lymph draining from the liver usually has a protein

With aging.

The oxidative capacity of the liver decreases with aging, and therefore any medications that require oxidation (for instance, benzodiazepines) are

Clinical significance.

Disease.

The liver is a vital organ and supports almost every other organ in the body. Because of its strategic location and multidimensional functions, the liver is also prone to many diseases. The bare area of the liver is a site that is vulnerable to the passing of infection from the abdominal cavity to the thoracic cavity. Liver diseases may be diagnosed by liver function tests–blood tests that can identify various markers. For example, acute-phase reactants are produced by the liver in response to injury or inflammation.  Hepatitis is a common condition of inflammation of the liver. The most usual cause of this is viral, and the

Symptoms.

The classic symptoms of

Diagnosis.

The diagnosis of liver disease is made by liver function tests, groups of blood tests, that can readily show the extent of liver damage. If infection is suspected, then other serological tests will be carried out. A physical examination of the liver

Liver regeneration.

The liver is the only human internal organ capable of natural regeneration of lost tissue; as little as 25% of a liver can regenerate into a whole liver. This is, however, not true regeneration but rather compensatory growth in mammals. The lobes that are removed do not regrow and the growth of the liver is a restoration of function, not original form. This contrasts with true regeneration where both original function and form are restored. In some other species, such as zebrafish, the liver undergoes true regeneration by restoring both shape and size of the organ. In the liver, large areas of the tissues are formed but for the formation of new cells there must be sufficient amount of material so the circulation of the blood becomes more active.

Liver transplantation.

Human liver transplants were first performed by Thomas Starzl in the United States and Roy Calne in Cambridge, England in 1963 and 1967, respectively.  Liver transplantation is the only option for those with irreversible liver failure. Most transplants are done for chronic liver diseases leading to cirrhosis, such as chronic hepatitis C, alcoholism, and autoimmune hepatitis. Less commonly, liver transplantation is done for fulminant hepatic failure, in which liver failure occurs over days to weeks.  Liver allografts for transplant usually come from donors who have died from fatal brain injury. Living donor liver transplantation is a technique in which a portion of a living person's liver is removed (hepatectomy) and used to replace the entire liver of the recipient. This was first performed in 1989 for pediatric liver transplantation. Only 20 percent of an adult's liver (Couinaud

Society and culture.

Some cultures regard the liver as the seat of the soul. In Greek mythology, the gods punished Prometheus for revealing fire to humans by chaining him to a rock where a vulture (or an eagle) would peck out his liver, which would regenerate overnight. (The liver is the only human internal organ that actually can regenerate itself to a significant extent.) Many ancient peoples of the Near East and Mediterranean areas practiced a type of divination called haruspicy or hepatomancy, where they tried to obtain information by examining the livers of sheep and other animals.  In Plato, and in later physiology, the liver was thought to be the seat of the darkest emotions (specifically wrath, jealousy and greed) which drive men to action. The Talmud (tractate "Berakhot 61b") refers to the liver as the seat of anger, with the gallbladder counteracting this. The Persian, Urdu, and Hindi languages (جگر or जिगर or "jigar") refer to the liver figurative speech to indicate courage and strong feelings, or "their best"; e.g., "This Mecca has thrown to you the pieces of its liver!". The term "jan e jigar", literally "the strength (power) of my liver", is a term of endearment in Urdu. In Persian slang, "jigar" is used as an adjective for any object which is desirable, especially women. In the Zulu language, the word for liver (isibindi) is the same as the word for courage.

Food.

Humans commonly eat the livers of mammals, fowl, and fish as food. Domestic pig, ox, lamb, calf, chicken, and goose livers are widely available from butchers and supermarkets. In the Romance languages, the anatomical word for "liver" (French "foie", Spanish "hígado", etc.) derives not from the Latin anatomical term, "jecur", but from the culinary term "ficatum", literally "stuffed with figs," referring to the livers of geese that had been fattened on figs. Animal livers are rich in iron, vitamin A and vitamin B; and cod liver oil is commonly used as a dietary supplement.  Liver can be

Giraffe liver.

The Humr, one of the tribes in the Baggara ethnic grouping, native to southwestern Kordofan in Sudan and speakers of Shuwa or Chadian Arabic, prepare a non-alcoholic drink from the liver and bone marrow of the giraffe which they call "umm nyolokh", and which they claim is intoxicating ( Arabic سكران "sakran" ), causing dreams and even waking hallucinations. Anthropologist Ian Cunnison, who accompanied the Humr on one of their giraffe-hunting expeditions in the late 1950s, notes that:  It is said that a person, once he has drunk "umm nyolokh", will return to giraffe again and again. Humr, being Mahdists, are strict abstainers [ from alcohol ] and a Humrawi is never drunk ( "sakran" ) on liquor or beer. But he uses this word to describe the effects which "umm nyolokh" has upon him.  Cunnison's remarkable account of an apparently psychoactive mammal found

Arrow/bullet poison.

Certain Tungusic peoples formerly prepared a type of arrow poison from rotting animal livers, which was, in later times, also applied to bullets. Russian anthropologist Sergei Mikhailovich Shirokogorov notes that: Formerly the using of poisoned arrows was common. For instance, among the Kumarčen, [ a subgroup

Other animals.

The liver is found in all vertebrates and is typically the largest visceral (internal) organ. Its form varies considerably in different species, and is largely determined by the shape and arrangement of the surrounding organs. Nonetheless, in most species it is divided into right and left lobes; exceptions to this general rule include snakes, where the shape of the body necessitates a simple cigar-like form. The internal structure of the liver is broadly similar in all vertebrates.  An organ sometimes referred to as a liver is found associated with the digestive tract of the primitive chordate "Amphioxus". Although it performs many functions of a liver, it is not considered a true liver but a homolog of the vertebrate liver. The amphioxus hepatic caecum produces the liver-specific proteins vitellogenin, antithrombin, plasminogen, alanine aminotransferase, and insulin/Insulin-like growth factor (IGF)

The liver is an organ only found in vertebrates which detoxifies various metabolites, synthesizes proteins and produces biochemicals necessary for digestion and growth. In humans, it is located in the right upper quadrant of the abdomen, below the diaphragm. Its other roles in metabolism include the regulation of glycogen storage, decomposition of red blood cells, and the production of hormones.

肝脏(英语:liver)为脊椎动物体内的一种器官,以代谢功能为主,并扮演着除去毒素,储存糖原(肝糖),分泌蛋白质合成等重要角色。肝脏也会制造胆汁。在医学用字上,常以拉丁语字首"hepato-"或"hepatic"来描述肝脏。


Fundamentals.

Lasers are distinguished from other light sources by their coherence. Spatial coherence is typically expressed through the output being a narrow beam, which is diffraction-limited. Laser beams can be focused to very tiny spots, achieving a very high irradiance, or they can have very low divergence in order to concentrate their power at a great distance. Temporal (or longitudinal) coherence implies a polarized wave at a single frequency, whose phase is correlated over a relatively great distance (the coherence length) along the beam. A beam produced by a thermal or other incoherent light source has an instantaneous amplitude and phase that vary randomly with respect to time and position, thus having a short coherence length.  Lasers are characterized according to their wavelength in a vacuum. Most "single wavelength" lasers actually produce radiation in several "modes" with slightly different wavelengths. Although temporal coherence implies monochromaticity, there are lasers that emit a broad spectrum of light or emit different wavelengths of light simultaneously. Some lasers are not single spatial mode and have light beams that diverge more than is required by the diffraction limit. All such devices are classified as "lasers" based on their method of producing light, i.e., stimulated emission. Lasers are employed where light of the required spatial or temporal coherence can not be produced using simpler technologies.

Terminology.

The word "laser" started as an acronym for "light amplification by stimulated emission of radiation". In this usage, the term "light" includes electromagnetic radiation of any frequency, not only visible light, hence the terms "infrared laser", "ultraviolet laser", "X-ray laser" and "gamma-ray laser". Because the microwave predecessor of the laser, the maser, was developed first, devices of this sort operating at microwave and radio frequencies are referred to as "masers" rather than "microwave lasers" or "radio lasers". In the early technical literature, especially at Bell Telephone Laboratories, the laser was called an optical maser; this term is

Design.

A laser consists of a gain medium, a mechanism to energize it, and something to provide optical feedback. The gain medium is a material with properties that allow it to amplify light by way of stimulated emission. Light of a specific wavelength that passes through the gain medium is amplified (increases in power).  For the gain medium to amplify light, it needs to be supplied with energy in a process called pumping. The energy is typically supplied as an electric current or as light at a different wavelength. Pump light may

Laser physics.

Electrons and how they interact with electromagnetic fields are important in our understanding of chemistry and physics.

Stimulated emission.

In the classical view, the energy of an electron orbiting an atomic nucleus is larger for orbits further from the nucleus of an atom. However, quantum mechanical effects force electrons to take on discrete positions in orbitals. Thus, electrons are found in specific energy levels of an atom, two of which are shown below:  An electron in an atom can absorb energy from light (photons) or heat (phonons) only if there is a transition between energy levels that matches the energy carried by the photon or phonon. For light, this means that any given transition will only absorb one particular wavelength of light. Photons with

Gain medium and cavity.

The gain medium is put into an excited state by an external source of energy. In most lasers this medium consists of a population of atoms which have been excited into such a state by means of an outside light source, or an electrical field which supplies energy for atoms to absorb and be transformed into their excited states.  The gain medium of a laser is normally a material of controlled purity, size, concentration, and shape, which amplifies the beam by the process of stimulated emission described

The light emitted.

In most lasers, lasing begins with spontaneous emission into the lasing mode. This initial light is then amplified by stimulated emission in the gain medium. Stimulated emission produces light that matches the input signal in direction, wavelength, and polarization, whereas the phase of emitted light is 90 degrees in lead of the stimulating light. This, combined with the filtering effect of the optical resonator gives laser light its characteristic coherence, and may give it uniform polarization and monochromaticity, depending on the resonator's design. The fundamental laser linewidth of light emitted from the lasing resonator can be orders of magnitude narrower than the linewidth of light emitted from the passive resonator. Some lasers use a separate injection seeder to start the process off with a beam that is already highly coherent. This can produce beams with a narrower spectrum than would otherwise be possible.  Many lasers produce a beam that can be approximated as a Gaussian beam; such beams have the minimum divergence possible for a given beam diameter. Some lasers, particularly high-power ones, produce multimode beams, with the transverse modes often approximated using Hermite–Gaussian or Laguerre-Gaussian functions. Some high power lasers use

Quantum vs. classical emission processes.

The mechanism of producing radiation in a laser relies on stimulated emission, where energy is extracted from a transition in an atom or molecule. This is a quantum phenomenon discovered by Albert Einstein who derived

Continuous and pulsed modes of operation.

A laser can be classified as operating in either continuous or pulsed mode, depending on whether the power output is essentially continuous over time or whether its output takes the form of pulses of light on one or another time scale. Of course even a laser whose output is normally continuous can be intentionally turned on and off at some rate in order to create pulses of light. When the modulation rate is on time scales much slower than the cavity lifetime and the time period over which energy can be stored in the lasing medium or pumping mechanism, then it is still classified as a "modulated" or "pulsed" continuous wave laser. Most laser diodes used in communication systems fall in that category.

Continuous wave operation.

Some applications of lasers depend on a beam whose output power is constant over time. Such a laser is known as "continuous wave" ("CW"). Many types of lasers can be made to operate in continuous wave mode to satisfy such an application. Many of these lasers actually lase in several longitudinal modes at the same time, and beats between the slightly different optical frequencies of those oscillations will, in fact, produce amplitude variations on time scales shorter than the round-trip time (the reciprocal of the frequency spacing between modes), typically a

Pulsed operation.

Pulsed operation of lasers refers to any laser not classified as continuous wave, so that the optical power appears in pulses of some duration at some repetition rate. This encompasses a wide range of technologies addressing a number of different motivations. Some lasers are pulsed simply because they cannot be run in continuous mode.  In other cases, the application requires the production of pulses having as large an energy as possible. Since the pulse energy is equal to the average power divided by the repetition rate, this goal can sometimes be satisfied by lowering the rate of pulses so that more energy can be built up in between pulses. In laser ablation, for example, a

Q-switching.

In a Q-switched laser, the population inversion is allowed to build up by introducing loss inside the resonator which exceeds the gain of the medium; this can also be described as a reduction of the quality factor or 'Q' of the cavity. Then, after

Mode-locking.

A mode-locked laser is capable of emitting extremely short pulses on the order of tens of picoseconds down to less than 10 femtoseconds. These pulses will repeat at the round trip time, that is, the time that it takes light to complete one round trip between the mirrors comprising the resonator. Due to the Fourier limit (also known as energy-time uncertainty), a pulse of such short temporal length has a spectrum spread over a considerable bandwidth. Thus such

Pulsed pumping.

Another method of achieving pulsed laser operation is to pump the laser material with a source that is itself pulsed, either through electronic charging in the case of flash lamps, or another laser which is already pulsed. Pulsed pumping was historically used with dye lasers where the inverted population lifetime of a dye molecule was so short that a high energy, fast pump was needed. The way to overcome this problem was to charge up large capacitors which are then switched to discharge through flashlamps, producing an intense flash. Pulsed pumping is also required for three-level lasers in which the lower energy level rapidly becomes highly populated preventing further lasing until those atoms relax to the ground state. These lasers, such as the excimer laser and the copper vapor laser, can never be operated in CW mode.

History.

Foundations.

In 1917, Albert Einstein established the theoretical foundations for the laser and the maser in the paper "Zur Quantentheorie der Strahlung" (On the Quantum Theory of Radiation) via a re-derivation of Max Planck's law of radiation, conceptually based upon probability coefficients (Einstein coefficients) for the absorption, spontaneous emission, and stimulated emission of electromagnetic radiation.

Maser.

In 1951, Joseph Weber submitted a paper on using stimulated emissions to make a microwave amplifier to the June 1952 Institute of Radio Engineers Vacuum Tube Research Conference at Ottawa, Ontario, Canada. After this presentation, RCA asked Weber to give a seminar on this idea, and Charles Hard Townes asked him for a copy of the paper.  In 1953, Charles Hard Townes and graduate students James P. Gordon and Herbert J. Zeiger produced the first microwave amplifier, a device operating on similar principles to the laser, but amplifying microwave radiation rather than infrared or visible radiation. Townes's maser was incapable of continuous output. Meanwhile, in the Soviet Union, Nikolay

Laser.

In 1957, Charles Hard Townes and Arthur Leonard Schawlow, then at Bell Labs, began a serious study of the infrared laser. As ideas developed, they abandoned infrared radiation to instead concentrate upon visible light. The concept originally was called an "optical maser". In 1958, Bell Labs filed a patent application for their proposed optical maser; and Schawlow and Townes submitted a manuscript of their theoretical calculations to the "Physical Review", published that year in Volume 112, Issue No. 6.  Simultaneously, at Columbia University, graduate student Gordon Gould was working on a doctoral thesis about the

Recent innovations.

Since the early period of laser history, laser research has produced a variety of improved and specialized laser types, optimized for different performance goals, including: and this research continues to this day.  In 2015, researchers made a white laser, whose light is modulated by a synthetic nanosheet made out of zinc, cadmium, sulfur, and selenium that can emit red, green, and blue light in varying proportions, with each wavelength spanning 191 nm.  In 2017, researchers

Types and operating principles.

Gas lasers.

Following the invention of the HeNe gas laser, many other gas discharges have been found to amplify light coherently. Gas lasers using many different gases have been built and used for many purposes. The helium–neon laser (HeNe) is able to operate at a number of different wavelengths, however the vast majority are engineered to lase at 633 nm; these relatively low cost but highly coherent lasers are extremely common in optical research and educational laboratories. Commercial carbon dioxide (CO) lasers can emit many hundreds of watts in a single spatial mode which can be concentrated into a tiny spot. This emission is in the

Chemical lasers.

Chemical lasers are powered by a chemical reaction permitting a large amount of energy to be released quickly. Such very high power lasers are especially of interest to the military, however continuous wave chemical lasers

Excimer lasers.

Excimer lasers are a special sort of gas laser powered by an electric discharge in which the lasing medium is an excimer, or more precisely an exciplex in existing designs. These are molecules which can only exist with one atom in an excited electronic state. Once the molecule transfers its excitation energy to a photon, its atoms are no longer bound to each other and the molecule disintegrates. This drastically reduces the population of the lower energy state thus greatly facilitating a population inversion. Excimers currently used are all ; noble gasses are chemically inert and can only form compounds while in an excited state. Excimer lasers typically operate at ultraviolet wavelengths with major applications including semiconductor photolithography and LASIK eye surgery. Commonly used excimer molecules include ArF (emission at 193 nm), KrCl (222 nm), KrF (248 nm), XeCl (308 nm), and XeF (351 nm). The molecular fluorine laser, emitting at 157 nm in the vacuum ultraviolet is sometimes referred to as an excimer laser, however this appears to be a misnomer inasmuch as F is a stable compound.

Solid-state lasers.

Solid-state lasers use a crystalline or glass rod which is "doped" with ions that provide the required energy states. For example, the first working laser was a ruby laser, made from ruby (chromium-doped corundum). The population inversion is actually maintained in the dopant. These materials are pumped optically using a shorter wavelength than the lasing wavelength, often from a flashtube or from another laser. The usage of the term "solid-state" in laser physics is narrower than in typical use. Semiconductor lasers (laser diodes) are typically "not" referred to as solid-state lasers.  Neodymium is a common dopant in various solid-state laser crystals, including yttrium orthovanadate (Nd:YVO), yttrium lithium fluoride () and yttrium aluminium garnet (). All these lasers can produce high powers in the infrared spectrum at 1064 nm. They are used for cutting, welding and marking of metals and other materials, and also in spectroscopy and for pumping dye lasers. These lasers are also commonly frequency doubled, tripled or quadrupled to produce 532

Fiber lasers.

Solid-state lasers or laser amplifiers where the light is guided due to the total internal reflection in a single mode optical fiber are instead called fiber lasers. Guiding of light allows extremely long gain regions providing good cooling conditions; fibers have high surface area to volume ratio which allows efficient cooling. In addition, the fiber's waveguiding properties tend to reduce thermal distortion of the beam. Erbium and ytterbium ions are common active species in such lasers.  Quite often, the fiber laser is designed as a double-clad fiber. This type of fiber consists of a fiber core, an inner cladding and an outer cladding. The index of the three concentric layers is chosen so that

Photonic crystal lasers.

Photonic crystal lasers are lasers based on nano-structures that provide the mode confinement and the density

Semiconductor lasers.

Semiconductor lasers are diodes which are electrically pumped. Recombination of electrons and holes created by the applied current introduces optical gain. Reflection from the ends of the crystal form an optical resonator, although the resonator can be external to the semiconductor in some designs.  Commercial laser diodes emit at wavelengths from 375 nm to 3500 nm. Low to medium power laser diodes are used in laser pointers, laser printers and CD/DVD players. Laser diodes are also frequently used to

Dye lasers.

Dye lasers use an organic dye as the gain medium. The wide gain spectrum of available dyes, or mixtures of dyes, allows these lasers to be highly tunable, or to produce very short-duration pulses

Free-electron lasers.

Free-electron lasers, or FELs, generate coherent, high power radiation that is widely tunable, currently ranging in wavelength from microwaves through terahertz radiation and infrared to the visible spectrum, to soft X-rays. They have the widest frequency

Exotic media.

The pursuit of a high-quantum-energy laser using transitions between isomeric states of an atomic nucleus has been the subject of wide-ranging academic research since the early 1970s. Much of this is summarized in three review articles. This research has been international in scope, but mainly based in the former Soviet Union and the United States. While many scientists remain optimistic that a breakthrough is near, an operational gamma-ray laser is yet to be realized.  Some of the early studies were directed toward short pulses of neutrons exciting the upper isomer state in a solid so the gamma-ray transition could benefit from the line-narrowing of Mössbauer effect. In conjunction, several advantages were expected from two-stage pumping of a three-level system. It was conjectured that the nucleus of an atom, embedded in the near field of a laser-driven coherently-oscillating electron cloud would experience

Uses.

When lasers were invented in 1960, they were called "a solution looking for a problem". Since then, they have become ubiquitous, finding utility in thousands of highly varied applications in every section of modern society, including consumer electronics, information technology, science, medicine, industry, law enforcement, entertainment, and the military. Fiber-optic communication using lasers is a key technology in modern communications, allowing services such as the Internet.  The first widely noticeable use of lasers was the supermarket barcode scanner, introduced in 1974. The laserdisc player, introduced in 1978, was the first successful consumer product to include a laser but the compact disc player was the first laser-equipped device to become common, beginning in 1982 followed shortly by laser printers.  Some other uses are:  In 2004, excluding diode lasers, approximately 131,000 lasers were sold with a value of US$2.19 billion. In the same year, approximately 733 million diode lasers, valued at $3.20 billion, were sold.

In medicine.

Lasers have many uses in medicine, including laser surgery (particularly eye surgery), laser healing, kidney stone treatment, ophthalmoscopy, and cosmetic skin treatments such as acne treatment, cellulite and striae reduction, and hair removal.  Lasers are used to treat cancer by shrinking or destroying tumors or precancerous growths. They are most commonly used to treat superficial cancers that are on the surface of the body or the lining of internal

As weapons.

A laser weapon is a

Hobbies.

In recent years, some hobbyists have taken interests in lasers. Lasers used by hobbyists are generally of class IIIa or IIIb (see Safety), although some have made their own class IV types. However, compared to other hobbyists, laser hobbyists are far less common, due to the cost

Examples by power.

Different applications need lasers with different output powers. Lasers that produce a continuous beam or a series of short pulses can be compared on the basis of their average power. Lasers that produce

Safety.

Even the first laser was recognized as being potentially dangerous. Theodore Maiman characterized the first laser as having a power of one "Gillette" as it could burn through one Gillette razor blade. Today, it is accepted that even low-power lasers with only a few milliwatts of output power can be hazardous to human eyesight when the beam hits the eye directly or after reflection from a shiny surface. At wavelengths which the cornea and the lens can focus well, the coherence and low divergence of laser light means that it can be focused by the eye into an extremely small spot on the retina, resulting in localized burning and permanent damage in seconds or even less time.  Lasers are usually labeled with a safety class number, which identifies how dangerous the laser is: The indicated powers are for visible-light, continuous-wave lasers. For pulsed lasers and invisible wavelengths, other power limits apply. People working with class 3B and class 4 lasers can protect their eyes with safety goggles which are designed to absorb light of a particular wavelength.  Infrared lasers with wavelengths longer than about 1.4 micrometers are often referred to as "eye-safe", because the cornea tends to absorb light at these wavelengths, protecting the retina from damage. The label "eye-safe" can be misleading, however, as it applies only to relatively low power continuous wave beams; a high power or Q-switched laser at these wavelengths can burn the cornea, causing severe eye damage, and even moderate power lasers can injure the eye.  Lasers can be a hazard to both civil and military aviation, due to the potential to temporarily distract or blind pilots. See Lasers and aviation safety for more on this topic.  Cameras based on charge-coupled devices may actually be more sensitive to laser damage than biological eyes.

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term "laser" originated as an acronym for "light amplification by stimulated emission of radiation". The first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow.

,是“通过受激辐射产生的光放大”(英语:Light Amplification by Stimulated Emission of Radiation)的缩写。指通过刺激原子导致电子跃迁释放辐射能量而产生的具有同调性(Coherence)的增强光子束。其特点包括发散度极小、亮度(功率)很高、单色性好、相干性好等。产生激光需要“激发来源”、“增益介质”、“共振结构”这三个要素。


Description.

The diversity of characteristics complicates any description of the Liliaceae morphology, and confused taxonomic classification for centuries. The diversity is also of considerable evolutionary significance, as some members emerged from shaded areas and adapted to a more open environment (see Evolution).

General.

The Liliaceae are characterised as monocotyledonous, perennial, herbaceous, bulbous (or rhizomatous in the case of Medeoleae) flowering plants with simple trichomes (root hairs) and contractile roots. The flowers may be arranged (inflorescence) along the stem, developing from the base, or as a single flower at the tip of the stem, or as a cluster of flowers. They contain both male (androecium) and female (gynoecium) characteristics and are symmetric radially, but sometimes as a mirror image. Most flowers are large and colourful, except for Medeoleae. Both the petals and sepals are usually similar and appear as two concentric groups (whorls) of 'petals', that are often striped or multi-coloured, and produce nectar at their bases. The stamens are usually in two groups of three (trimerous) and the pollen has a single groove (monosulcate). The ovary is placed above the attachment of the other parts (superior). There are three fused carpels (syncarpus) with one to three chambers (locules), a single style and a three-lobed stigma. The embryo sac is of the "Fritillaria" type. The fruit is generally a wind dispersed capsule, but occasionally a berry (Medeoleae) which is dispersed by animals. The leaves are generally simple and elongated with veins parallel to the edges, arranged singly and alternating on the stem, but may form a rosette at the base of the stem.

Specific.

Characteristics often vary by habitat, between shade-dwelling genera (such as "Prosartes", "Tricyrtis", "Cardiocrinum", "Clintonia", "Medeola", "Prosartes", and "Scoliopus") and sun loving genera. Shade-dwelling genera usually have broader leaves with smooth edges and net venation, and fleshy fruits (berries) with animal-dispersed seeds, rhizomes, and small, inconspicuous flowers while genera native to sunny habitats usually have narrow, parallel-veined leaves, capsular fruits with wind-dispersed seeds, bulbs, and large, visually conspicuous flowers. (See also "Evolution").

Taxonomy.

The taxonomy of the Liliaceae has a very complex history. The family was first described in the eighteenth century, and over time many other genera were added until it became one of the largest of the monocotyledon families, and also extremely diverse. Modern taxonomic systems, such as the APG which is based on phylogenetic principles using molecular biology, have redistributed many of these genera resulting in the relatively small family that is currently recognised. Consequently, there are many different accounts of the Liliaceae in the literature and older uses of the term occur commonly. To distinguish between them, the Latin terms "sensu lato" and "sensu stricto" are frequently used (together with their abbreviations, "s.l." and "s.s.") to denote the broader or stricter sense of the circumscription respectively, e.g. Liliaceae "s.s.".

History.

The family Liliaceae was described by Michel Adanson in 1763 and formally named by Antoine Laurent de Jussieu in 1789. Jussieu defined this grouping as having a calyx of six equal colored parts, six stamens, a superior ovary, single style, and a trilocular (three-chambered) capsule. By 1845, John Lindley, the first English systematist unhappily acknowledged the great diversity in the circumscription of the family, and that it had expanded vastly, with many subdivisions. As he saw it, the Liliaceae were already paraphyletic ("catch-all"), being all Liliales not included in the other orders, but hoped that the future would reveal some characteristic that would group them better. He recognized 133 genera and 1200 species. By the time of the next major British classification – that of Bentham and Hooker in 1883 (published in Latin) – several of Lindley's other families had already been absorbed into the Liliaceae. Over time the family became increasingly broad and somewhat arbitrarily defined as all species of plants with six tepals and a superior ovary, eventually coming to encompass about 300 genera and 4,500 species within the order Liliales under the Cronquist system (1981). Cronquist merged the Liliaceae with the Amaryllidaceae, making this one of the largest monocotyledon families.  Many other botanists echoed Lindley's earlier concerns about the phylogeny of the Liliaceae, but various schemes to divide the family gained little traction. Dahlgren (1985) suggested there were in fact forty – not one – families distributed over three orders (predominantly Liliales and Asparagales). In the context of a general review of the classification of angiosperms, the Liliaceae were subjected to more intense scrutiny. Considerable progress in plant phylogeny and phylogenetic theory enabled a phylogenetic tree to be constructed for all of the flowering plants, as elaborated by the Angiosperm Phylogeny Group (1998).

Modern APG classification and phylogeny.

The Angiosperm Phylogeny Group (APG) made rapid progress in establishing a modern monophyletic classification of the flowering plants by 2009. Despite establishing this relative degree of monophyly (genetic homogeneity) for the family Liliaceae, their morphology remains diverse and there exists within the Liliaceae clade or grouping, a number of subclades (subgroups). Particularly enigmatic were "Clintonia", "Medeola", "Scoliopus", and "Tricyrtis".  Of the fifteen genera within the Liliaceae, the ten genera of the Lilioideae subfamily form one morphological group that is characterised by contractile bulbs and roots, and a Fritillaria-type embryo-sac (megagametophyte with four megaspores). Within the Lilioideae, "Clintonia" and the closely related "Medeola" form a subclade, and are now considered a separate tribe (Medeoleae). The other major grouping consists of the five genera constituting the Streptopoideae (including "Scoliopus") and Calochortoideae (including "Tricyrtis") subfamilies characterised by creeping rhizomes, styles which are divided at their apices, and by megagametophyte development of the "Polygonum"-type (a simple megaspore and triploid endosperm) embryo-sac.

Evolution and biogeography.

The development of a phylogenetic approach to taxonomy suggested the Liliales formed some of the earliest monocots. Molecular analysis indicates that divergence amongst the Liliales probably occurred around 82 million years ago. The closest sister family to the Liliaceae are the Smilacaceae with the Liliaceae separating 52 million years ago. Liliaceae thus arose during the late (Maastrichtian) Cretaceous to early (Paleocene) Paleogene periods. Major evolutionary clades include the Lilieae ("Lilium, Fritillaria, Nomocharis, Cardiocrinum, Notholirion") from the Himalayas about 12 mya and the Tulipeae ("Erythronium", "Tulipa", "Gagea") from East Asia at about the same time. The Medeoleae ("Clintonia" and "Medeola") may have appeared in North America but were subsequently dispersed, as may have the Streptopoideae and Calochortoideae. Liliaceae fossils have been dated to the Paleogene and Cretaceous eras in the Antarctic.  The Liliaceae probably arose as shade plants, with subsequent evolution to open areas including deciduous forest in the more open autumnal period, but then a return of some species (e.g. "Cardiocrinum"). This was accompanied by a shift from rhizomes to bulbs, to more showy flowers, the production of capsular fruit and narrower parallel-veined leaves. Again, some reversal to the broader reticulate-veined leaves occurred (e.g. "Cardiocrinum")

Subdivisions and genera.

Suprageneric subdivisions.

Due to the diversity of the originally broadly defined Liliaceae "s.l.", many attempts have been made to form suprageneric classifications, e.g. subfamilies and tribes. Classifications published since the use of molecular methods in phylogenetics have taken a narrower view of the Liliaceae (Liliaceae "s.s."). The Angiosperm Phylogeny Website (APweb) recognizes three subfamilies, one of which is divided into two tribes.

Genera.

Various authorities (e.g. ITIS 16, GRIN 27, WCSP, NCBI, DELTA ) differ on the exact number of genera included in Liliaceae "s.s.", but generally there are about fifteen to sixteen genera, depending on whether or not "Amana" is included in "Tulipa" and "Lloydia" in "Gagea". For instance "Amana" is still listed separately in WCSP.  Currently the APWeb lists fifteen genera, arranged as shown in this table :  The largest genera are "Gagea" (200), "Fritillaria" (130), "Lilium" (110), and "Tulipa" (75 species), all within the tribe Lilieae.

Etymology and pronunciation.

The name "Liliaceae" () comes to international scientific vocabulary from New Latin, from "Lilium", the type genus, + "-aceae", a standardized suffix for plant family names in modern taxonomy. The genus name comes from the Classical Latin word "lilium", "lily", which in turn came from the Greek "" ().

Distribution and habitat.

The Liliaceae are widely distributed, but mainly in the temperate regions of the Northern Hemisphere. The centre of diversity is from southwest Asia to China. Their distribution is diverse, mainly in plains, steppes, and alpine meadows, but also in deciduous forests, Mediterranean scrub and arctic tundra. "Tulipa" and "Gagea" provide examples of ornamental geophyte biomorphological types representing continental thermoperiodic zones (Irano-Turanian region), characterised by cessation of underground growth at high temperatures in early summer and requiring low winter temperatures for spring flowering. While some genera are shade-dwelling, such as the Medeoleae, and Streptopoideae, "Tricyrtis", and "Cardiocrinum", others prefer a more open habitat.

Ecology.

The Liliaceae are ecologically diverse. Species of Liliaceae bloom at various times from spring to late summer. The colorful flowers produce large amounts of nectar and pollen that attract insects which pollinate them (entomophily), particularly bees and wasps (hymenopterophily), butterflies (psychophily) and moths (phalaenophily). The seeds are dispersed by wind and water. Some species (e.g. "Scoliopus", "Erythronium and Gagea") have seeds with an aril structure that are dispersed by ants (myrmecochory).  The proliferation of deer populations in many areas, due to human factors such as the elimination of their animal predators and introduction to alien environments, is placing considerable herbivory pressure on many of the family's species. Fences as high as 8 feet may be required to prevent them from consuming the plants, an impractical solution for most wild areas. Those of the genus "Lilium" are particularly palatable, while species in "Fritillaria" are repellant.

Pests and predators.

Liliaceae are subject to a wide variety of diseases and pests, including insects, such as thrips, aphids, beetles and flies. Also fungi, viruses and vertebrate animals such as mice and deer. An important horticultural and garden pest is the scarlet lily beetle (Japanese red lily beetle, "Lilioceris lilii") and other Lilioceris species which attack "Fritillaria" and "Lilium". "Lilium" species may be food plants for the Cosmia trapezina moth. A major pest of Tulips is the fungus, "Botrytis tulipae".  Both "Lilium" and "Tulipa" are susceptible to a group of five viruses of the family "Potyviridae", specifically the potyvirus (named for "potato virus Y)" group, which includes the "tulip-breaking virus" ("TBV") and the "lily streak virus" (lily mottle virus, "LMoV") resulting in 'breaking' of the color of the flowers. The viruses are transmitted by aphids. This breaking effect was of economic importance during the tulip mania of the seventeenth century, because it appeared to be producing new varieties. In modern times tulip breeders have produced varieties that mimic the effect of the virus, without being infected. One of these varieties is known as 'Rembrandt', after the Dutch artist of that name. Contemporary tulip owners commonly had Rembrandt and other artists paint their flowers to preserve them for posterity, hence the 'broken' tulips were known as Rembrandt tulips at that time. Another modern variety is 'Princess Irene'. One of the tulip breaking viruses is also named the "Rembrandt tulip-breaking virus" (ReTBV).

Cultivation.

Floriculture.

Many species of Lilieae (in genera "Tulipa", "Fritillaria", "Lilium", and "Erythronium") and Calochortoideae ("Calochortus" and "Tricyrtis") are grown as ornamental plants worldwide. Within these genera a wide range of cultivars have been developed by breeding and hybridisation. They are generally used in outdoor gardens and other displays, although in common with many bulbous flowering plants they are often induced to bloom indoors, particularly during the winter months. They also form a significant part of the cut flower market, in particular "Tulipa" and "Lilium".

Tulips.

Tulips have been cultivated since at least the tenth century in Persia. Tulip production has two main markets: cut flowers and bulb. The latter are used, in turn, to meet the demand for bulbs for parks, gardens and home use and, secondly, to provide the necessary bulbs for cut flower production. International trade in cut flowers has an approximate total value of 11 billion euros, which provides an indication of the economic importance of this activity. The main producer of tulip bulbs is the Netherlands, a country that accounts for 87% of the global cultivated area, with approximately 12,000 hectares. Other leading producers include Japan, France and Poland. Approximately ten other countries produce commercial tulips, largely for the domestic market. By contrast, the Netherlands is the leading international producer, to the extent of 4 billion bulbs per annum. Of these, 53% are used for the cut flower market and the remainder for the dry bulb market. Of the cut flowers, 57% are used for the domestic market in the Netherlands and the remainder exported.  Original "Tulipa" species can be obtained for ornamental purposes, such as "Tulipa tarda" and "Tulipa turkestanica". These are referred to as species, or botanical, tulips, and tend to be smaller plants but better at naturalising than the cultivated forms. Breeding programs have produced a wide range of tulip types, enabling blooming through a much longer season by creating early, mid- and late spring varieties. Fourteen distinct types are available in addition to botanical tulips, including Lily-flowered, Fringed, Viridiflora and Rembrandt. In addition to blooming season, tulip varieties differ in shape, and height, and exhibit a wide range of colours, both pure and in combination.

Lilies.

The largest area of production is also the Netherland, with 76% of the global cultivated area, followed by France, Chile, Japan, the United States, New Zealand and Australia. Approximately ten countries produce lilies commercially altogether. About half of the commercial production is for cut flowers. Many of these countries export bulbs as well as supplying the domestic market. The Netherland produces about 2,200 million lily bulbs annually, of which 96% is used domestically and the remainder exported, principally within the European Union. One particularly important crop is the production of "Lilium longiflorum", whose white flowers are associated with purity and Easter.  Although many "Lilium" species such as "Lilium martagon" and "Lilium candidum" can be obtained commercially, the majority of commercially available lilies represent the products of a very diverse hybridisation program, which has resulted in a separate horticultural classification, including such groupings as Asian, Oriental and Orienpet. In addition to a very wide variety of heights, lilies can be obtained in many colours and combinations of colours, and if properly selected can produce an extensive blooming season from early summer to autumn. Because of the history of Liliaceae, many species such as Watsonia (bugle lily) that were previously classified in this family bear the name 'lily' but are neither part of the genus "Lilium", or the family Liliaceae.

Other.

A variety of "Fritillaria" species are used as early spring ornamental flowers. These vary from the large "Fritillaria imperialis" (crown imperial) available in a number of colours such as yellow or orange, to the relatively tiny species such as "Fritillaria meleagris" or "Fritillaria uva-vulpis" with their chequered patterns. "Erythronium" is less common but a popular cultivar is 'Pagoda' with its sulphur yellow flowers. "Calochortus" (mariposa lily) may be sold as a mixture or as cultivars.

Propagation.

Methods of propagation include both sexual and asexual reproduction. Commercial cultivars are usually sterile.

Sexual reproduction.

Seeds can be used for propagation of the plant or to create hybrids and can take five to eight years to produce flowering plants. Since interspecific cross-pollination occurs, overlapping wild populations can create natural hybrids.

Asexual reproduction.

Bulb offsets and tissue culture produce genetic clones of the parent plant and thus maintaining genetic integrity of the cultivars. Bulb offsets usually require at least a year before flowering. Commercially, plants may be propagated in vitro and then planted out to grow into plants large enough to sell.

Toxicology.

While members of the Liliaceae "s.s." have been used as food sources in humans, the bulbs of some species are poisonous to household pets (bulb toxicosis) if eaten and may cause serious complications, such as kidney failure in cats from Lilies, particularly "Lilium longiflorum" (Easter Lily). Dogs may develop less serious effects such as gastrointestinal problems and central nervous system depression. Most Fritillaria (e.g. "Fritillaria imperialis", "Fritillaria meleagris") bulbs contain poisonous neurotoxic alkaloids such as imperialin (peiminine), which may be deadly if ingested in quantity, while other species such as Fritillaria camschatcensis and "Fritillaria affinis" are edible. Tulips can cause skin irritation due to the presence of tuliposides and tulipalins, which are also found in the flowers, leaves and stems of "Fritillaria". These are also toxic to a variety of animals.

Uses.

Fritillaria extracts are used in traditional Chinese medicine under the name "chuan bei mu", and in Latin, "bulbus fritillariae cirrhosae". The bulbs of "Fritillaria roylei" have been used as antipyretics and expectorants. "Lilium" bulbs, particularly Lanzhou lily ("Lilium davidii") are used as food in China and other parts of Asia. During World War II, starvation conditions in the Netherlands ("Hongerwinter", hunger winter 1944) led to using "Tulipa" bulbs as food. "Calochortus" bulbs were eaten by Native Americans and by the Mormon settlers in Utah during starvation. Other members of the family used for food include "Clintonia" (leaves), "Medeola" (roots), "Erythronium" (corms), and "Fritillaria" (bulbs).

Culture.

Lilies.

The type genus, Lily ("Lilium"), has a long history in literature and art, and a tradition of symbolism as well as becoming a popular female name, and a floral emblem, particularly of France (fleur-de-lis). The cultivation of lilies has been described since at least the ninth century, when Charlemagne ordered it to be grown at his imperial palaces. However, the name 'lily' has historically been applied to a wide variety of plants other than the genus "Lilium".  The lily appears in ancient literature associated with both sovereignty and virginal innocence, and is mentioned on a number of occasions in the Bible, such as the description in Solomon's Song of Songs (2, 1–2) ""I am a rose of Sharon, a lily of the valleys. Like a lily among thorns is my darling among the young women"" or the Gospel of Mathew (6, 28) ""Consider the lilies of the field, how they grow; they toil not, neither do they spin"" to represent beauty. Artistic representations can be found as far back as frescos from the second century BC, at Amnisos and Knossos. Early Christian churches, such as that of the Basilica of Sant' Apollinare in Classe were sometimes decorated with lilies. While predominantly depicted as white, those seen at Akrotiri are red lilies. The white lily has long been seen as a symbol of purity, coming to be associated with the Virgin Mary in the Middle Ages, from which came the name ‘Madonna lily’ ("Lilium candidum"). A well-known example is Leonardo da Vinci's "Annunciation" (1472–1475) in which the archangel Gabriel bears a Madonna lily. Other symbolic meanings include glory, love and birth.

Fleur-de-lis.

The stylised lily, or "fleur-de-lis" (lily flower) has long been associated with royalty, although it may originally have been derived from the form of an iris. It has also been associated with the head of a spear. Its three parts have been associated with the three classes of mediaeval society, or alternatively faith, wisdom and chivalry. Whatever its exact derivation, it has come to be associated with France and the French monarchy since the earliest Frankish kings. Consequently, it became incorporated into not only French heraldry but also that of many heraldic devices in jurisdictions where there had been historic French influence, such as Quebec and New Orleans. In modern times it appears in many forms, symbolic and decorative, and can be used on compasses to indicate the direction north, as well as the Scouting movement.

Tulips.

Tulips ("Tulipa") also have a long cultural tradition, particularly in the Islamic world. The Persian word for tulips, "lâleh" (), was borrowed into Turkish and Arabic as "lale". In Arabic letters, "lale" is written with the same letters as "Allah", and is used to denote God symbolically. Tulips became widely used in decorative motifs on tiles, fabrics, and ceramics in Islamic art and the Ottoman Empire in particular, and were revered in poetry, such as that of Omar Khayam in the twelfth century.  Tulips were an essential part of the gardens of Persia, having been cultivated from the Steppes. As the Seljuks – Oghuz-Turkic leaders originated from the steppes – moved to Persia, and then west, they took tulips with them to Turkey, where many escaped cultivation and became naturalised. Today there are a number of places in Turkey called "Laleli" (‘with tulips’). Tulips first appeared in the decorative arts in Turkey in the thirteenth century and flourished under the Ottomans, in particular in the royal palaces, and was adopted by the Osmans as their symbol. Further species were collected from Persia and the spreading Ottoman Empire saw to it that tulip culture also spread. By the sixteenth century it was a national symbol, hence the designation "Tulip era", by which time they were becoming of economic importance.  By 1562 the tulip trade had reached Europe with the first shipment to Antwerp, where they were mistaken for vegetables, although they had been cultivated in Portugal since 1530, and first appeared in illustration in 1559, and the first tulip flowers were seen in the Netherlands in 1625. Tulips spread rapidly across Europe in the seventeenth century, and became an important trading item, initially in France before concentrating in the Netherlands. Eventually speculative trading in tulips became so intense as to cause a financial bubble which eventually collapsed, a period known as tulip mania (tulipomania), from 1634 to 1637, similar to the Ottoman Empire's Tulip era.  Nevertheless, since then the tulip has become indelibly associated with the Netherlands and all things Dutch. it was during this period that the tulipiere, a ceramic vase for growing tulips indoors was devised, and the Golden Age of Dutch Painting was replete with images of tulips. Although tulip festivals are held around the world in the spring, the most famous of these is the display at Keukenhof. One of the better-known novels on tulips is "The Black Tulip" by Alexandre Dumas, père in 1850, dealing with a contest to grow a black tulip in late seventeenth-century Haarlem.

Other.

"Fritillaria" are also often used as floral emblems, for instance as the county flower of Oxfordshire, UK. "Calochortus nuttallii", the sego lily, is the official state flower of Utah.

The lily family, Liliaceae, consists of about 254 (or 15) genera and about 4075 (or 610) known species of flowering plants within the order Liliales. They are monocotyledonous, perennial, herbaceous, often bulbous geophytes. Plants in this family have evolved with a fair amount of morphological diversity despite genetic similarity. Common characteristics include large flowers with parts arranged in threes: with six colored or patterned petaloid tepals (undifferentiated petals and sepals) arranged in two whorls, six stamens and a superior ovary. The leaves are linear in shape, with their veins usually arranged parallel to the edges, single and arranged alternating on the stem, or in a rosette at the base. Most species are grown from bulbs, although some have rhizomes. First described in 1789, the lily family became a paraphyletic "catch-all" (wastebasket) group of petaloid monocots that did not fit into other families and included a great number of genera now included in other families and in some cases in other orders. Consequently, many sources and descriptions labelled "Liliaceae" deal with the broader sense of the family.

百合科(学名:)植物是被子植物的一种,属单子叶植物类。百合科植物在全世界都分布得比较广泛,特别是温带和亚热带地区。传统分类法的百合科曾多达230属3500种,而经被子植物种系发生学组依基因分子学研究结果大幅修定后,目前仅包含17个属,常见的品种有百合花、郁金香、贝母等。