A Potentilla flower with nectar guides on its yellow petals. Here, under ultra-violet light, the petals lose their colour, while the nectar guides become visible to the human eye. Nectar guides serve as a visual signal to attract bees to the flower nectaries. The eye of a bee is sensitive to ultra-violet light, and thus the bee detects these nectar guides as prominent dark patches on the petals leading to the centre of the flower. While the bee is feeding on nectar, it disperses pollen and so ensures that the flower is pollinated. (see B760/233 for a view of the Potentilla flower under normal light).