A Flower's Colour

A flower's colour, [blank] , isn't a full-proof guide to a good lunch. That's because the colour can change depending on the angle at which sunlight hits its petals. A yellow flower, for example, may look somewhat blue from one angle and red from another. Scientists call this kind of colour [blank] iridescence. "It's the same phenomenon that makes a rainbow appear in a soap bubble or on a CD," says Beverley Glover. She studies plants at the University of Cambridge in England.In 2009, Glover and her colleagues showed that even [blank] petals look shimmery, bees can still tell which flowers likely hold food. But she and others noticed something odd about iridescence. "It's not quite as flashy in plants as in other life forms," Glover says. The backs of jewels, beetles, or the wings of certain butterflies, for instance, shine and shimmer a lot more.The researchers tested their hypothesis in the lab. They trained a group of bees to associate fake purple flowers with getting more nectar. Then the team [blank] the bees. They added non-shimmery fake flowers with purple-blue and purple-red hues to the bees' flight path. The bees passed the test, ignoring flowers that weren't [blank] purple.Second group of bees was [blank] to drink from fully flashy, 'perfectly iridescent' purple flowers. But when the team added perfectly iridescent flowers in different hues, the insects checked them for nectar too.