''Claviceps purpurea'' is an

ergot Ergot ( ) or ergot fungi refers to a group of fungi of the genus ''Claviceps''. The most prominent member of this group is '' Claviceps purpurea'' ("rye ergot fungus"). This fungus grows on rye and related plants, and produces alkaloids that c ...

fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

that grows on the ears of rye and related

cereal A cereal is any grass cultivated for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, germ, and bran. Cereal grain crops are grown in greater quantities and provide more food ...

and

forage Forage is a plant material (mainly plant leaves and stems) eaten by grazing livestock. Historically, the term ''forage'' has meant only plants eaten by the animals directly as pasture, crop residue, or immature cereal crops, but it is also use ...

plants. Consumption of

grain A grain is a small, hard, dry fruit ( caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legum ...

s or seeds contaminated with the survival structure of this fungus, the ergot sclerotium, can cause

ergotism Ergotism (pron. ) is the effect of long-term ergot poisoning, traditionally due to the ingestion of the alkaloids produced by the '' Claviceps purpurea'' fungus—from the Latin "club" or clavus "nail" and for "head", i.e. the purple club-he ...

in humans and other mammals. ''C. purpurea'' most commonly affects

outcrossing Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity. Outcrossing can be a usefu ...

species such as rye (its most common host), as well as

triticale Triticale (; × ''Triticosecale'') is a hybrid of wheat (''Triticum'') and rye (''Secale'') first bred in laboratories during the late 19th century in Scotland and Germany. Commercially available triticale is almost always a second-generation ...

wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...

and

barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley p ...

. It affects oats only rarely.

Life cycle

Claviceps purpurea - Köhler–s Medizinal-Pflanzen-185-en

An ''ergot kernel'' called ''Sclerotium clavus'' develops when a floret of flowering grass or cereal is infected by an

ascospore An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera ...

of ''C. purpurea''. The infection process mimics a

pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametop ...

grain growing into an

ovary The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...

during

fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Pro ...

. Because infection requires access of the fungal spore to the stigma, plants infected by ''C. purpurea'' are mainly

species with open flowers, such as rye (''

Secale cereale Rye (''Secale cereale'') is a grass grown extensively as a grain, a cover crop and a forage crop. It is a member of the wheat tribe (Triticeae) and is closely related to both wheat (''Triticum'') and barley (genus ''Hordeum''). Rye grain i ...

'') and

Alopecurus ''Alopecurus'', or foxtail grass, is a common and widespread genus of plants in the grass family. It is common across temperate and subtropical parts of Eurasia, northern Africa, and the Americas, as well as naturalized in Australia and on vari ...

. The proliferating fungal

mycelium Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrates. A typical single spore germinates ...

then destroys the plant ovary and connects with the

vascular bundle A vascular bundle is a part of the transport system in vascular plants. The transport itself happens in the stem, which exists in two forms: xylem and phloem. Both these tissues are present in a vascular bundle, which in addition will inc ...

originally intended for feeding the developing

seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosper ...

. The first stage of ergot infection manifests itself as a white soft tissue (known as ''Sphacelia segetum'') producing sugary honeydew, which often drops out of the infected grass florets. This honeydew contains millions of asexual spores (

conidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non- motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to t ...

) which are dispersed to other florets by

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...

s or rain. Later, the ''Sphacelia segetum'' convert into a hard dry ''Sclerotium clavus'' inside the husk of the floret. At this stage,

alkaloid Alkaloids are a class of basic, naturally occurring organic compounds that contain at least one nitrogen atom. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of simila ...

s and

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids in ...

s (e.g.

ricinoleic acid Ricinoleic acid, formally called 12-hydroxy-9-''cis''-octadecenoic acid is a fatty acid. It is an unsaturated omega-9 fatty acid and a hydroxy acid. It is a major component of the seed oil obtained from mature castor plant (''Ricinus communis'' ...

) accumulate in the Sclerotium. When a mature ''Sclerotium'' drops to the ground, the fungus remains dormant until proper conditions trigger its fruiting phase (onset of spring, rain period, need of fresh temperatures during winter, etc.). It germinates, forming one or several fruiting bodies with head and stipe, variously colored (resembling a tiny

mushroom A mushroom or toadstool is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground, on soil, or on its food source. ''Toadstool'' generally denotes one poisonous to humans. The standard for the name "mushroom" is ...

). In the head, threadlike sexual spores (ascospores) are formed in

perithecia An ascocarp, or ascoma (), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. Ascocarps are mos ...

, which are ejected simultaneously, when suitable grass hosts are flowering. Ergot infection causes a reduction in the yield and quality of grain and hay produced, and if infected grain or hay is fed to livestock it may cause a disease called

. '' Polistes dorsalis'', a species of social wasps, have been recorded as a vector of the spread of this particular fungus. During their foraging behavior, particles of the fungal conidia get bound to parts of this wasp's body. As ''P. dorsalis'' travels from source to source, it leaves the fungal infection behind. Insects, including flies and moths, have also been shown to carry conidia of ''Claviceps'' species, but if insects play a role in spreading the fungus from infected to healthy plants is unknown.

Intraspecific variations

Early scientists have observed ''Claviceps purpurea'' on other

Poaceae Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns an ...

as ''

''. 1855, Grandclement described ergot on '' Triticum aestivum''. During more than a century scientists aimed to describe specialized species or specialized varieties inside the species ''Claviceps purpurea''. * ''Claviceps microcephala'' Tul. (1853) * ''Claviceps wilsonii'' Cooke (1884) Later scientists tried to determine host varieties as * ''Claviceps purpurea'' var. ''agropyri'' * ''Claviceps purpurea'' var. ''purpurea'' * ''Claviceps purpurea'' var. ''spartinae'' * ''Claviceps purpurea'' var. ''wilsonii''. Molecular biology has not confirmed this hypothesis but has distinguished three groups differing in their ecological specificity. * G1—land grasses of open meadows and fields; * G2—grasses from moist, forest, and mountain habitats; * G3 (''C. purpurea'' var. ''spartinae'')—salt marsh grasses (Spartina, Distichlis). Morphological criteria to distinguish different groups: The shape and the size of sclerotia are not good indicators because they strongly depend on the size and shape of the host floret. The size of conidia can be an indication but it is weak and it is necessary to pay attention to that, due to osmotic pressure, it varies significantly if the spores are observed in honeydew or in water. The sclerotial density can be used as the groups G2 and G3 float in water. The compound of alkaloids is also used to differentiate the strains.

Host range

Pooideae

Agrostis canina ''Agrostis canina'', the velvety bentgrass, brown bent or velvet bent, is a species of grass in the family Poaceae. Description ''Agrostis canina'' is a perennial plant, with stolons but no rhizomes, and culms which grow to a height of up ...

'', ''

Alopecurus myosuroides ''Alopecurus myosuroides'' is an annual grass, native to Eurasia, found in moist meadows, deciduous forests, and on cultivated and waste land. It is also known as slender meadow foxtail, black-grass, twitch grass, and black twitch. Description ...

'' (G2), '' Alopecurus arundinaceus'' (G2), ''

Alopecurus pratensis ''Alopecurus pratensis'', known as the meadow foxtail or the field meadow foxtail, is a perennial grass belonging to the grass family (Poaceae). It is native to Europe and Asia. This common plant is found on grasslands, especially on neutral s ...

'', '' Bromus arvensis'', ''

Bromus commutatus ''Bromus commutatus'', the meadow brome, is an Annual plant, annual or biennial plant, biennial species of plant in the grass family (biology), family Poaceae. In the United States it is known as hairy chess. Description The height ranges from 4 ...

'', ''

Bromus hordeaceus ''Bromus hordeaceus'', the soft brome, is an annual or biennial species of grass in the true grass family ( Poaceae). It is also known in North America as bull grass, soft cheat, and soft chess. It is the most common species of ''Bromus'' in Bri ...

'' (G2), ''

Bromus inermis ''Bromus inermis'' is a species of the true grass family (Poaceae). This rhizomatous grass is native to Europe and North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisph ...

'', '' Bromus marginatus'', '' Elymus tsukushiense'', '' Festuca arundinacea'', ''

Elymus repens ''Elymus repens'', commonly known as couch grass, is a very common perennial species of grass native to most of Europe, Asia, the Arctic biome, and northwest Africa. It has been brought into other mild northern climates for forage or erosion cont ...

'' (G1), '' Nardus stricta'', '' Poa annua'' (G2), ''

Phleum pratense Timothy (''Phleum pratense'') is an abundant perennial grass native to most of Europe except for the Mediterranean region. It is also known as timothy-grass, meadow cat's-tail or common cat's tail. It is a member of the genus '' Phleum'', consi ...

'', ''

Phalaris arundinacea ''Phalaris arundinacea'', or reed canary grass, is a tall, perennial bunchgrass that commonly forms extensive single-species stands along the margins of lakes and streams and in wet open areas, with a wide distribution in Europe, Asia, norther ...

'' (G2), '' Poa pratensis'' (G1), ''

Stipa ''Stipa'' is a genus of around 300 large perennial hermaphroditic grasses collectively known as feather grass, needle grass, and spear grass. They are placed in the subfamily Pooideae and the tribe Stipeae, which also contains many species for ...

''.

Arundinoideae

Danthonia ''Danthonia'' is a genus of Eurasian, North African, and American plants in the grass family. Members of this genus are sometimes referred to as oatgrass, but that common name is not restricted to this genus. Other common names include heathgrass ...

'', ''

Molinia caerulea ''Molinia caerulea'', known by the common name purple moor-grass, is a species of grass that is native to Europe, west Asia, and north Africa. It grows in locations from the lowlands up to in the Alps. Like most grasses, it grows best in acid so ...

''.

Chloridoideae

'' Spartina'', '' Distichlis'' (G3)

Panicoideae

Setaria ''Setaria'' is a widespread genus of plants in the grass family. The name is derived from the Latin word ''seta'', meaning "bristle" or "hair", which refers to the bristly spikelets. The genus includes over 100 species distributed in many tr ...

Epidemiology

''Claviceps purpurea'' has been known to humankind for a long time, and its appearance has been linked to extremely cold winters that were followed by rainy springs. The sclerotial stage of ''C. purpurea'' conspicuous on the heads of ryes and other such grains is known as ergot. Sclerotia germinate in spring after a period of low temperature. A temperature of 0-5 °C for at least 25 days is required. Water before the cold period is also necessary. Favorable temperatures for stroma production are in the range of 10-25 °C. Favorable temperatures for mycelial growth are in the range of 20-30 °C with an optimum at 25 °C. Sunlight has a chromogenic effect on the

with intense coloration.

Effects

The disease cycle of the ergot fungus was first described in 1853, but the connection with ergot and epidemics among people and animals was reported already in a scientific text in 1676. The ergot sclerotium contains high concentrations (up to 2% of dry mass) of the

ergotamine Ergotamine, sold under the brand names Cafergot (with caffeine) and Ergomar among others, is an ergopeptine and part of the ergot family of alkaloids; it is structurally and biochemically closely related to ergoline. It possesses structural sim ...

, a complex molecule consisting of a tripeptide-derived cyclol-lactam ring connected via

amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it i ...

linkage to a lysergic acid (ergoline) moiety, and other alkaloids of the ergoline group that are biosynthesized by the fungus. Ergot alkaloids have a wide range of biological activities including effects on circulation and

neurotransmission Neurotransmission (Latin: ''transmissio'' "passage, crossing" from ''transmittere'' "send, let through") is the process by which signaling molecules called neurotransmitters are released by the axon terminal of a neuron (the presynaptic neuron), ...

Ergotism Ergotism (pron. ) is the effect of long-term ergot poisoning, traditionally due to the ingestion of the alkaloids produced by the '' Claviceps purpurea'' fungus—from the Latin "club" or clavus "nail" and for "head", i.e. the purple club-he ...

is the name for sometimes severe pathological syndromes affecting humans or animals that have ingested ergot alkaloid-containing plant material, such as ergot-contaminated grains. Monks of the order of St.

Anthony the Great Anthony the Great ( grc-gre, Ἀντώνιος ''Antṓnios''; ar, القديس أنطونيوس الكبير; la, Antonius; ; c. 12 January 251 – 17 January 356), was a Christian monk from Egypt, revered since his death as a saint. He is d ...

specialized in treating ergotism victims with balms containing tranquilizing and circulation-stimulating plant extracts; they were also skilled in amputations. The common name for ergotism is "St. Anthony's Fire", in reference to monks who cared for victims as well as symptoms, such as severe burning sensations in the limbs. These are caused by effects of ergot alkaloids on the

vascular system The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, t ...

due to

vasoconstriction Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vess ...

of blood vessels, sometimes leading to

gangrene Gangrene is a type of tissue death caused by a lack of blood supply. Symptoms may include a change in skin color to red or black, numbness, swelling, pain, skin breakdown, and coolness. The feet and hands are most commonly affected. If the gan ...

and loss of limbs due to severely restricted blood circulation. The neurotropic activities of the ergot alkaloids may also cause

hallucinations A hallucination is a perception in the absence of an external stimulus that has the qualities of a real perception. Hallucinations are vivid, substantial, and are perceived to be located in external objective space. Hallucination is a combinati ...

and attendant irrational behaviour, convulsions, and even death. Other symptoms include strong

uterine The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...

contractions,

nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of th ...

seizure An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with lo ...

s, and unconsciousness. Since the Middle Ages, controlled doses of ergot were used to induce

abortion Abortion is the termination of a pregnancy by removal or expulsion of an embryo or fetus. An abortion that occurs without intervention is known as a miscarriage or "spontaneous abortion"; these occur in approximately 30% to 40% of pre ...

s and to stop maternal bleeding after childbirth.Untersuchungen über das Verhalten der Secalealkaloide bei der Herstellung von Mutterkornextrakten. Labib Farid Nuar. Universität Wien - 1946 - (University of Vienna) Ergot alkaloids are also used in products such as

Cafergot Caffeine/ergotamine (trade name Cafergot) is the proprietary name of a medication consisting of ergotamine tartrate and caffeine. This combination is used for the treatment of headaches, such as migraine headache. Use Correct timing of use i ...

(containing

caffeine Caffeine is a central nervous system (CNS) stimulant of the methylxanthine chemical classification, class. It is mainly recreational drug use, used recreationally as a Nootropic, cognitive enhancer, increasing alertness and attentional perfor ...

and

or ergoline) to treat migraine headaches. Ergot extract is no longer used as a

pharmaceutical A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the medical field and ...

preparation. Ergot contains no

lysergic acid diethylamide Lysergic acid diethylamide (LSD), also known colloquially as acid, is a potent psychedelic drug. Effects typically include intensified thoughts, emotions, and sensory perception. At sufficiently high dosages LSD manifests primarily mental, vi ...

(LSD) but rather ergotamine, which is used to synthesize lysergic acid, an analog of and precursor for synthesis of LSD. Moreover, ergot sclerotia naturally contain some amounts of lysergic acid.

Culture

Potato dextrose agar Potato dextrose agar (BAM Media M127
from the U.S.

, wheat seeds or oat flour are suitable substrates for growth of the fungus in the laboratory. Agricultural production of Claviceps purpurea on rye is used to produce ergot alkaloids. Biological production of ergot alkaloids is also carried out by saprophytic cultivations.

Speculations

During the

Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...

, human poisoning due to the consumption of rye bread made from ergot-infected grain was common in Europe. These epidemics were known as Saint Anthony's fire, or ''ignis sacer''. Gordon Wasson proposed that the psychedelic effects were the explanation behind the festival of

Demeter In ancient Greek religion and Greek mythology, mythology, Demeter (; Attic Greek, Attic: ''Dēmḗtēr'' ; Doric Greek, Doric: ''Dāmā́tēr'') is the Twelve Olympians, Olympian goddess of the harvest and agriculture, presiding over crops, ...

at the

Eleusinian Mysteries The Eleusinian Mysteries ( el, Ἐλευσίνια Μυστήρια, Eleusínia Mystḗria) were initiations held every year for the cult of Demeter and Persephone based at the Panhellenic Sanctuary of Elefsina in ancient Greece. They are t ...

, where the initiates drank

kykeon Kykeon (, ; from , "to stir, to mix") was an Ancient Greek drink of various descriptions. Some were made mainly of water, barley and naturally occurring substances. Others were made with wine and grated cheese. It is widely believed that kykeon u ...

''.'' Linnda R. Caporael posited in 1976 that the hysterical symptoms of young women that had spurred the

Salem witch trials The Salem witch trials were a series of hearings and prosecutions of people accused of witchcraft in colonial Massachusetts between February 1692 and May 1693. More than 200 people were accused. Thirty people were found guilty, 19 of whom w ...

had been the result of consuming ergot-tainted rye. However, her conclusions were later disputed by Nicholas P. Spanos and Jack Gottlieb, after a review of the historical and medical evidence. Other authors have likewise cast doubt on ergotism having been the cause of the Salem witch trials. The

Great Fear The Great Fear (french: Grande Peur) was a general panic that took place between 22 July to 6 August 1789, at the start of the French Revolution. Rural unrest had been present in France since the worsening grain shortage of the spring, ...

in France during the

Revolution In political science, a revolution (Latin: ''revolutio'', "a turn around") is a fundamental and relatively sudden change in political power and political organization which occurs when the population revolts against the government, typically due ...

has also been linked by some historians to the influence of ergot. British author John Grigsby claims that the presence of ergot in the stomachs of some of the so-called 'bog-bodies' (

Iron Age The Iron Age is the final epoch of the three-age division of the prehistory and protohistory of humanity. It was preceded by the Stone Age ( Paleolithic, Mesolithic, Neolithic) and the Bronze Age ( Chalcolithic). The concept has been mostly ...

human remains from peat bogs N E Europe such as

Tollund Man The Tollund Man (died 405–380 BC) is a naturally mummified corpse of a man who lived during the 5th century BC, during the period characterised in Scandinavia as the Pre-Roman Iron Age. He was found in 1950, preserved as a bog body, near ...

), reveals that ergot was once a ritual drink in a prehistoric fertility cult akin to the

cult of ancient

Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders wi ...

. In his book Beowulf and Grendel he argues that the

Anglo-Saxon The Anglo-Saxons were a cultural group who inhabited England in the Early Middle Ages. They traced their origins to settlers who came to Britain from mainland Europe in the 5th century. However, the ethnogenesis of the Anglo-Saxons happened wit ...

poem

Beowulf ''Beowulf'' (; ang, Bēowulf ) is an Old English epic poem in the tradition of Germanic heroic legend consisting of 3,182 alliterative lines. It is one of the most important and most often translated works of Old English literature. ...

is based on a memory of the quelling of this fertility cult by followers of

Odin Odin (; from non, Óðinn, ) is a widely revered god in Germanic paganism. Norse mythology, the source of most surviving information about him, associates him with wisdom, healing, death, royalty, the gallows, knowledge, war, battle, victory, ...

. He states that Beowulf, which he translates as ''barley-wolf'', suggests a connection to ergot which in German was known as the 'tooth of the wolf'. An outbreak of violent hallucinations among hundreds of residents of Pont St. Esprit in 1951 in the south of France has also been attributed to ergotism. Seven people died.

References

External links

Claviceps purpurea - Ergot Alkaloid

* ttp://content.nejm.org/cgi/content/short/356/1/29 New England Journal of Medicine - Dopamine Agonists and the Risk of Cardiac-Valve Regurgitation
Linnda Caporeal's article "Ergotism: The Satan Loosed in Salem?
{{Taxonbar, from=Q217227 Clavicipitaceae Fungi of Europe Psychoactive fungi Natural sources of lysergamides Medicinal fungi Parasitic fungi Fungal plant pathogens and diseases Cereal diseases Barley diseases Rye diseases Triticale diseases Wheat diseases Abortifacients Soma (drink) Fungi described in 1823 Taxa named by Elias Magnus Fries

Life cycle

Intraspecific variations

Host range

Pooideae

Arundinoideae

Chloridoideae

Panicoideae

Epidemiology

Effects

Culture

Speculations

See also

References

External links