Sprengel demonstrated for the first time that the whole structure of nectar-bearing flowers is adapted for fertilization by insects. In his study of the Rose-bay Sprengel discovered dichogamy – that in some plants the two sexes (stigmas and anthers) while occurring in one blossom, mature at different times. This prevents the flowers from being fertilized by their own pollen, and necessitates fertilization by the pollen carried to them by insects.