The beautiful snake's-head fritillary is the flower of Oxfordshire. In this episode we look closely at the flowers it produces. The snake's-head fritillary is the county flower of Oxfordshire. Some consider it mournful, because of its drooping flower heads and dark purple colour. But some individuals produce white flowers instead. In this episode we learn how two different colours might remain in a population and one possible explanation involves reliance on herd immunity - a key concept in the current coronavirus crisis