The petal of the buttercup
Put a buttercup flower under your chin and it will shine. Everyone knows this - at least, everyone who has tested it - and children have gone so far as to turn it into a game. For a long time, scientists have wondered what causes this. Now, a team of scientists from the departments of Plant Sciences and Physics at the University of Cambridge have finally found the answer. It turns out that it's all about anatomy.
Scientists have known for some time that the buttercup flower is yellow because of a particular pigment on its petals that absorbs the blue-green light in the spectrum, leaving the rest to be reflected. The extreme flatness of the cells in the epidermis of the petals makes for a strong reflection, and this accounts for the distinctive glossiness of the buttercup. But none of this was enough to explain the buttercup's remarkable ability to actually reflect light under a child's chin - or anyone else's chin, for that matter.
The key to the mystery, according to the Cambridge team, is the extremely ingenious design of the buttercup's petal. Imagine a stream of sunlight shining down on the flower's petals. The carotenoid pigment absorbs the blue-green part of the spectrum, and the remaining light - particularly the yellow - is left to its own devices.
The yellow light is reflected from the very flat epidermal cells of the petals - but also from the layer of air just underneath the epidermis. This double reflection results in a proportional boost to the natural brightness of the buttercup. Nature can be very refined when it wants to be.
Nature is also very intelligent. There may be a hidden purpose to the buttercup's glossiness. The more attractive and unique a flower's visual appearance is - or so the theory goes - the better chance it has of attracting the right kind of pollinating insects, and thus of multiplying the species.
Surely, in this case, the buttercup wins the day.