Close-up ultraviolet photo of a Lemon Balm (Melissa officinalis) flower. The small white flowers measure around 5 mm across and contain relatively large amounts of nectar, making them popular with bees.
In ultraviolet the area around the mouth of the flower appears darker than it does in visible light. This may help guide bees (which can see ultraviolet light) to the flower's nectar source. In turn this helps the flowers get pollinated.
Colour modified in PS CS5