Petal power

Petals pack a peck of power, just ask any florist. They make their living out of flowers' power to soothe agitated hearts and to melt fair maidens' hearts. And we've all heard - and hopefully heeded - the advice to stop and smell the roses; you'd have to be a bit of a deadhead to be unmoved by their heady perfume. But how often do we stop to ponder the simple truth, universal to every "thing" in the universe, that even petals had to be meticulously designed down to the last minute detail? Petals don't just look good to human eyes, they have to do a lot of hard biological work, such as attracting insects and providing a surface that bees won't slide right off, just for starters. Scientists have found that bees visit flowers whose petals have special cone-shaped cells that provide a velcro-like surface facilitating a firm grip.¹ And they have also discovered that, "Microscopic ridges contouring the surface of flower petals might play a role in flashing that come-hither look pollinating insects can't resist"² (top right). Only an unimaginably brilliant mind with unlimited capacity for both inventiveness and mathematical precision could have dreamed up and figured out all the physical, chemical, and biological properties of flowers.

Take, for instance, that flower property we take so completely for granted - their ability to open, to transform from lump into glamour queen. The Great Designer was faced with quite a challenge when it came to turning theory into practice. Nothing just happens; it has to be made to happen. Tell me, which requires a bigger brain; figuring out how something like flowering happens after the fact or figuring out how to make it happen? Even today, in spite of all their remarkable expertise, flowerologists confess that "the mechanisms of how lilies and other flowers bloom, and thus how they reveal the bright colors of their petals and adopt their characteristic shape, are not fully understood".³ Recently two researchers, Haiyi Liang and L. Mahadevan, have taken a considerable leap forward in understanding the process of blooming.⁴ Well, for one kind of flower, at

least.

These two scientists studied the common lily, Lilium Casablanca, and discovered that the process did not follow the predictions of petal theorists (surprise, surprise) who had expected that the pressure that must somehow be generated to get the job done came about as a result of growth of the midrib of each petal. Rather, the pressure is generated by differential growth around the margins of petals. It's all a bit over this little bear's head, I'm afraid, but let's give it our best shot.

The lily bud consists of three inner petals wrapped inside three outer sepals. The edges of the outer sepals are held inside grooves running along the central midribs of the inner petals, "forming a locking mechanism that holds the bud closed until the growth inside reaches a critical point". A clue to what might be involved comes from the simple fact that the blooming process takes between four and five days to complete. If, for instance, the mechanism involved rapidly filling empty cells with water akin to pumping water into a balloon, thus forcing the petals to inflate, the process would be much quicker. The long time involved suggested that the flower actually "grows" open. The three inner petals grow faster than the three outer sepals, causing a buildup of pressure. In addition, the edges of the petals grow faster than the "backbone" creating a distorting effect. Furthermore, the growth around the edges is not uniform but varies from point to point. A mathematical analysis reveals that all of these factors combine - with perfect timing, of course - to reach a critical point at which the pressure causes the petals to "burst" out of the sepals, while the differential growth across the surface of the petals between backbone and edge causes the petal to bend backwards at just the same time. Voila! One open flower.

Now is that brilliant or is that brilliant? You don't have to be nuts to suggest that such a mechanism gradually evolved over the course of millions of years of trial-and-error mutations and natural selection, but it would help.

¹ University of Cambridge (2009, May 15). How Bees Hold Onto Flowers: 'Velcro'-like Structures On Flower Petals Help Bees Stick. ScienceDaily. Retrieved May 25, 2011, from http://www.sciencedaily.com­ /releases/2009/05/090514125148.htm

² New study sheds light on plant cell nanoridges

³ The physics of blooming: Watch it unfold

⁴ Harvard University (2011, March 22). How the lily blooms: Ruffling at the edge of each petal drives the delicate flower to open. ScienceDaily. Retrieved May 25, 2011, from http://www.sciencedaily.com­ /releases/2011/03/110321161918.htm