The following red or blue plant pigments, which are anthocyan glucosides, have been isolated and studied (for the structural arrangement of the characteristic groups, see pages 116): from cornflower and roses, _cyanin_, C_{28}H_{31}O_{16}Cl (2 molecules glucose + cyanidin); from cranberries, _idain_, C_{21}H_{21}O_{10}Cl (galactose + cyanidin); from geranium, _pelargonin_, C_{27}H_{30}O_{15}Cl (2 molecules glucose + pelargonidin); from pæony, _pæonin_, C_{28}H_{33}O_{16}Cl (2 molecules glucose + pæonidin, a monomethyl cyanidin); from blue grapes, _[oe]nin_, C_{23}H_{25}O_{12}Cl (glucose + [oe]nidin); from whortle berry, _myrtillin_, C_{22}H_{23}O_{12}Cl (glucose + myrtillidin); from larkspur, _delphinin_, C_{41}H_{39}O_{21}Cl (2 molecules glucose + 2 molecules _p_-oxybenzoic acid + delphinidin); and from mallow, _malvin_, C_{29}H_{35}O_{17}Cl (2 molecules glucose + malvidin). The blue dye, indigo, is derived from a glucoside of an entirely different type, known as _indican_. Indican is readily extracted from the leaves of various species of indigo plants. When hydrolyzed, it yields glucose and _indoxyl_ (colorless). Indoxyl is easily oxidized to _indigotin_ (the deep blue dye known as "indigo"). The equations illustrating these changes are as follows: (_a_) C_{14}H_{17}O_{6}N + H_{2}O = C_{6}H_{12}O_{6} + C_{8}H_{7}ON Indican Glucose Indoxyl (_b_) 2C_{8}H_{7}ON + O_{2} = C_{16}H_{10}O_{2}N + 2H_{2}O Indoxyl Indigotin The structural relationships of indoxyl and indigotin may be illustrated by the following formulas: O O /\ /\ ║ ║ / \ / \___COH / \___C C____/ \ | | ║ | | | | | | | | C-H | | C=C | | \ /\ / \ /\ / \ / \ / \/ N \/ N N \/ | | | H H H Indoxyl Indigotin Natural indigo dye is prepared by fermentation of indigo leaves, the decay of the cell-walls liberating the enzymes in the tissues, which bring about the chemical changes illustrated in the above equations. THE CYANOPHORE GLUCOSIDES Several glucosides which yield hydrocyanic acid as one of the products of their hydrolysis are of common occurrence in plants. These are generally spoken of as the "cyanogenetic" glucosides; but as they do not actually produce cyanogen compounds, but only liberate them when hydrolyzed, the recently suggested term "cyanophore" undoubtedly more correctly indicates their properties.