The anthocyanins have been identified in the flowers, fruits or leaves of approximately 200 species of plants. The results have been combined with earlier data, to ascertain the frequency with which derivatives of the three main anthocyanidin types occur as flower pigments among the species so far examined. Classification of the natural habitats of the species examined shows that pelargonidin derivatives predominate in the flowers of tropical and subtropical species, while delphinidin derivatives are the commonest in temperate and alpine plants. The colours of tropical and subtropical flowers containing cyanidin or delphinidin derivatives are generally redder than those of temperate species containing the same anthocyanin. It is concluded that red-flowered forms have a greater survival value than blue in most tropical plants. On the basis of the anthocyanin present in the flowers of thirty-two species of Tulipa, the genus falls into two groups in accordance with the morphological classification.