O O ║ 1 1 ║ 1' /\ C /\ /\ C /\ / \ / \ / \ / \ / \ / \ | | | |2 2| | | |2' | | | |3 3| | | |3' \ / \ / \ / \ / \ / \ / \/ O \/ \/ C \/ 4 4 ║ 4' O Flavone Anthocyan 1 1 /\ O 5'____4' /\ O 5'____4' / \ / \____/ \ / \ / \____/ \ 2| | | \____/3' 2| | | \____/3' 3| | |5 1' 2' 3| | |6 1' 2' \ / \ / \ / \ / \/ C \/ 5 4 ║ 4 O The red dyes which were formerly obtained from madder, the powdered roots of _Rubia tinctoria_, but are now almost wholly artificially synthetized, consist of at least four different glucosides, the organic group of which, in each case, is an hydroxy-derivative of anthraquinone. The most important of these is _ruberythric acid_, composed of two molecules of glucose linked with one of alizarin (1,2, dioxyanthraquinone). _Xanthopurpurin_ contains 1,3, dioxyanthraquinone, which is isomeric with alizarin; and _rubiadin_ is a monomethyl (the CH_{3} being in the 4 position), derivative of this compound. _Purpurin_ is a glucoside of 1,2,4, trioxyanthraquinone. The soluble yellow pigments are generally glucosides of hydroxy-derivatives of xanthone or flavone, known as oxyxanthones or oxyflavones. The sugars which are united to these nuclei vary greatly, so that there are a great variety of yellow, white, or colorless flavone or xanthone pigment compounds. These compounds are almost universally present in plants. For example, one typical set of examinations of the wood, bark, leaves, and flowers of over 240 different species of tropical plants showed that flavone derivatives were present in every sample which was tested, the pigments being usually located in the powdery coating of the epidermis of the tissues. The following typical examples will serve to illustrate the composition and properties of the glucosides of this type.