A Potentilla flower with invisible nectar guides on its yellow petals. Here, in normal light, the nectar guides cannot be seen by the human eye. Nectar guides serve as a visual signal to attract bees to the flower nectaries. They can be seen in the ultra-violet light range. 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 B760/234 for a view of this Potentilla flower under ultra-violet light).