indigo snake: see racer.

indigo bunting or indigo bird: see bunting.

indigo [Span.; from Lat.,=Indian], important blue dyestuff used in printing inks and for vat dyeing of cotton (see dye). It was anciently produced in India and was known in Egypt, probably c.1600 B.C.; mummies of the XVIII dynasty have been discovered wrapped in indigo-dyed cloth. Indigo is obtained from leguminous plants of the genus Indigofera, chiefly from the Asian species Indigofera tinctoria, but also from several other species. The plants contain a colorless, soluble glucoside called indican. When the macerated plants are allowed to ferment in vats of water the colorless form of indigo is liberated; stirring of the liquid causes oxidation of the colorless material to form a blue sediment. The natural indigo gives a strong blue color of great permanence. Use of the natural dye greatly decreased after the synthesis of indigo was accomplished. Adolf von Baeyer was the first to synthesize it, but others developed the methods used for its commercial production from aniline and chloroacetic acid.

Nonvenomous snake (Drymarchon corais, family Colubridae) found from the southeastern U.S. to Brazil. The largest snake in the U.S., it has a record length of 9.2 ft (2.8 m). In the U.S. it is blue-black; southward it may have brown foreparts, and in the tropics it is often called brown snake. It kills small vertebrates, including venomous snakes, by crushing with its jaws and the weight of its coils, but is not a constrictor. In defense it hisses and vibrates its tail but rarely strikes. It may share a burrow with a gopher tortoise, for which it is often called gopher snake. It has been listed as an endangered species since the 1970s.

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Any shrub or herb in the genus Indigofera of the pea family (see legume). Most occur in warm climates and are silky or hairy. The leaves are usually divided into smaller leaflets. Small rose, purple, or white flowers are borne in spikes or clusters. The fruit is a pod. Some species, particularly I. sumatrana and I. arrecta, were once an important source of indigo dye, a deep navy blue.

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