A directional trend of floral evolution, due to the selective activity of pollinating insects, birds and bats, is here described and discussed. Six clearly distinguishable levels in the evolution of flower types are correlated with six corresponding stages of sensory development of pollinating insects (Figs. 1, 2). This sequence of floral evolution was used for classification of present-day flower types (Fig. 4), and for identification of flower imprints in fossilized clays, muds, and fine sands. It was also used as a practical yardstick to determine the relative sensory ability of various groups of pollinating insects to distinguish flower types (Fig. 3).