There's a folk-legend that holds that the best way to see if a kid loves butter is to hold a buttercup under their chin and see if it reflects gold-yellow light on the kid's skin. If it does, then clearly they love butter. It seems strange that this legend sprang up, since the surer test would clearly be giving a kid a tub of butter, a mound of mashed potatoes, and a spoon, and seeing if they go to work. But you know kids; they love their new technology.
Now, after centuries of superstitious buttercup-chin juxtaposition, Cambridge scientists have unraveled the deep mystery of buttercups. They now understand why the buttercup shines yellow light on anything near it, and this longstanding mystery has been ascribed to the cellular structure of the flower.
Scientists have been trying to figure out exactly why the buttercup tends to yellow up whatever is near it, more than any other flower. The flower's yellow coloration is a simple tendency of the petals to absorb blue-green light and reflect yellow light. The buttercups share this tendency with plenty of other flowers. What seems to make the difference is a unique top layer of the petals. Scientists have known for some time that the top layer of cells of the flower are stretched thin, making them shiny as glass, reflecting large amounts of light.
What's been recently discovered is a tiny layer of air between the gloss and the petals. This is a microscopic version of the layers of bubbles coating the hulls of ships, or hands dipped briefly under the water. The layers of air surrounded by glassy walls only slightly alter the color of the substance, but they throw off an immense amount of light, making the object shine. The same effect is happening with the buttercups. The thin layer of air reflects so much light that it doubles the amount of light coming off the buttercups. The result is a yellow glow that will act as a spotlight to pollinators and puts all the other flowers to shame.
But not as much shame as those kids should feel.
Image: Jonas Bergsten