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ANATOMY OF A ROSE -- EXPLORING THE SECRET LIFE OF FLOWERS |
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TWO: The Blind Voyeur WE WALK THROUGH A FIELD of wildflowers. Sweeps of purple run up a hill. Stopping, looking closer, we see red skyrocket, orange globemallow, blue flax, yellow marigold. Flowers surround us with brilliant pointillism. Something in our chest lightens, dislodges, and rises into song. We want to sing like a bird. We love flowers, obviously, because we love color. Human eyes process reflected light and pass that information on to the brain, where the real perception of color takes place. Color becomes wrapped in emotion and thought. Yellow is cheerful. Gray is sad. White is spiritual. People who have lost color sight describe a tear in the fabric of the world. One man saw his wife and friends as "animated gray statues." Food and sex became disgusting. Life seemed utterly wrong, dirty, unnatural. Most of us, most of the time, take color for granted. We hardly notice the gorgeous, cerulean sky. We are habituated to green, the miracle that sustains us. It takes a hot-pink geranium to break through our calm. We exclaim at the velvet red of a rose. We delight in the sudden orange, the streak of blue. Over 250,000 species of plants produce flowers, a vast array of color, scent, and form. This is pure spectacle, worthy of P. T. Barnum's greatest show on earth. But human beings are not the intended audience. We sit in the theater, applauding and adoring, yet we don't understand most of the performance. We miss some of the best tricks. Flowers have patterns we cannot see, and they reflect colors we cannot imagine. The red poppy is not red to the bumblebee. The yellow cinquefoil may not be yellow to the butterfly. The purple snapdragon shimmers oddly. Surrounded by flowers, witness to glory, we feel inspired. We feel grateful. Unknowing, we are not much more than blind voyeurs. ***
Spectrum I LIE DOWN IN THE GREEN grass, cuddling up to a patch of daisies, their centers the color of egg yolk, their petals a soft, milky white. Nearby, a red skyrocket (Ipomopsis aggregata) flaunts its long, trumpetlike, fused petals that end in a five-pointed, star-shaped opening. I only have a few minutes. Ants will begin to crawl up my ankle. Spiky leaves will tickle my skin. I will feel a growing uneasiness, so close to the ground, less than a foot high. I will feel, soon, the desire to stand and reclaim my bipedal perspective. For a few minutes, the white petals of the daisy hold me. The smell of earth and leaves is familiar. I am being rocked, lulled, slipping into a dream as the sun drenches this meadow with radiant energy that moves toward me in rhythmic waves. The longest wavelengths are radio waves, infrared, and near-infrared. The last is the heat on my bare leg. The shortest wavelengths are ultraviolet, X rays, and gamma rays; most of these will never reach the earth's surface. Between ultraviolet and near-infrared is the spectrum of visible light, those photons, or packets of energy, with wavelengths that the human eye can see. We perceive these different wavelengths as different colors. At one end of the spectrum is violet. At the other end is red. When I move slightly, the petals of the red skyrocket loom large, filling my vision. In the cells of these petals are pigments that either absorb or reflect the different wavelengths of light. The pigments of skyrocket reflect back photons in the red range. They absorb most of the other wavelengths, and I do not see these colors. The flower is keeping these colors. What I see is the reflected red light that enters my eye, where the pigments there transform it into electrochemical energy, which is sent to my brain. I think, "Scarlet." I think, "Matador." Although I understand all the words that explain light and the act of seeing red, the event itself is so fast and so complex that I do not understand, really, the sum of my words. I move my head again, toward the white daisy. In some white flowers, pigments in the cells of the petals reflect back all of the visible spectrum: red, orange, yellow, green, blue, and violet. When all the colors are reflected back from an object, we see white. Most white flowers do not rely on pigment. Instead, they have petals filled with air spaces that reflect light. For the same reason, snow looks white because of air spaces in the frozen crystals. Different arrangements of floral cells can cause a diffuse reflection or a high refraction, a velvety matte look or a shiny brightness. If you squeeze the petal of a flower with air spaces, the air will be expelled and the limp petal will look colorless. When the entire spectrum of visible light is absorbed by a petal, or by anything else, we see the color black. We do not see many black flowers. In 1939, one was reported to be growing in northern Oaxaca, Mexico. Fifty years later, a botanist went in search of the flower (Lisanthius nigrescens). He wrote that its buds were "glistening drops of coal oil," the open blossoms, an inch long, "bells of black satin." In the laboratory, he found that the petals were producing massive amounts of pigment, which absorbed wavelengths from red to violet at an incredible rate. No one knows what pollinates this flower. No one knows why a flower would dress in black. Green, of course, is a color I see everywhere in this meadow -- the dark green of the daisy's leaf, the light green of the skyrocket's stem, the emerald green of new grass, the distant green of juniper trees and ponderosa pine. In school, most of us learned about photosynthesis, a subject we might have done better to study in church. The pigment chlorophyll converts light to energy. We all depend on this act of grace. Chlorophyll absorbs best at wavelengths of violet-blue and orange-red. It reflects back and does not use wavelengths of green. Biologists think they know why. The ancestors of plants evolved at the bottom of a sea, under swarms of aquatic bacteria that were already absorbing and using the green wavelength. Plantlike cells that developed pigments that could absorb and use the remaining spectrum survived (and hence reproduced) better than other cells. Once on land, in full sunlight, plants didn't need to become more efficient. Plants continued to reflect green rather than absorb all wavelengths. Perhaps for this reason, we do not walk under trees of black satin or picnic in fields of coal-dark grass. I am grateful for serendipity. A bee comes to visit the daisy. The insect lands, plopping, thumping, shaking the flower. The daisy seems suddenly alert. The daisy seems suddenly relieved. Rocked in rhythmic waves, lulled by the sun, I would be the daisy's lover. I would embrace the red skyrocket, the purple verbena, the orange firewheel, the blue flax, the yellow groundsel. I yearn for the daisy, for color, for love. But I have no real sense of commitment. I have no intention of pollinating these flowers. And these flowers have not been waiting for me. THE BEE IS a serious pollinator. Bees include over 25,000 species, big, small, stingless, aggressive, social, and solitary. We have been studying bees for a long time, especially honeybees, and we are constantly amazed at what they can do. These tiny things dance. They communicate. They remember. They learn. Bees have been called the intellectuals of the insect world. (Butterflies, unfairly, are known as the dumb blondes.) Bees have taught us never to underestimate. Honeybees have three types of photoreceptors, or light-sensitive cells, with peak sensitivity in the areas of ultraviolet, blue, and green. Human beings see best in the areas of blue, green, and red. The reflection or absorption of ultraviolet light constantly affects how a bee sees the world. In my mountain meadow, I am struck by the popularity of yellow. In a range of species, in every shape and size, yellow flowers are everywhere. Yellow is bright. Yellow is cheerful. Was it on sale? To me, many yellow flowers simply look yellow, like the flowers of wormseed mustard, rape, and field mustard. But since each of these flowers reflects ultraviolet light differently, a bee will see three different colors. In human sight, the two ends of the spectrum, violet and red, combine to form purple. In bee sight, the two ends of the spectrum, ultraviolet and orange-red, combine to form what some scientists call "bee-purple." They could as reasonably say "foog" or "orumpho," a more alien word. When all the colors of the human spectrum are reflected back from an object, we see white. When all the colors of a bee's spectrum, including ultraviolet, are reflected back from an object, the bee sees "bee-white," a color we might not recognize. To a bee, most human-white flowers look blue-green, while the green leaves of this daisy probably look gray. Although bees do not see far in the red range, only a few flowers absorb a bee's entire spectrum and look "beeblack." Red flowers that reflect some blue light look blue. Red flowers that reflect ultraviolet look ultraviolet. What color is ultraviolet? What color is blue and ultraviolet? What color is yellow and ultraviolet? What colors, really, are all these flowers in this meadow? We don't know, since we can't see them. Perhaps nothing strains our imagination so much as an experience outside our evolution. We don't have the chemistry. We don't have the neurons. We can't make the color happen in our brain. The skyrocket bobbles in a breeze. This close, the vivid red shows tints of orange. Small, white spots decorate the inside of each flower's starlike opening and run deep into the corolla, the trumpet-shaped fused petals. Looking deeper still, a pink glow is visible. Once a flower has gotten a pollinator's attention, it may begin to use color differently. Guide marks, like these small, white spots, direct an animal to the source of nectar or pollen. Rings at the flower's center are the bull's-eye. Lines and arrows point dramatically. The yellow streak on an iris is a landing strip, signaling small aircraft. Rows of green dots lead the way in a marsh gentian. Orange markings do the same in a monkeyflower. Read the sign, please. Don't wait to be seated. Dinner is this way. Different parts of a flower, differently colored, also reflect or absorb ultraviolet light. Some guide marks are completely invisible to the human eye. I feel the frisson of a parallel world: flowers glowing in strange colors, flowers marked by strange patterns. Briefly, I want to see what the bee sees. Let me slip under the surface of this dream. Let me lift this veil before my eyes. *** THE FOSSILS OF THE EARLIEST KNOWN FLOWERS are about 120 million years old. Bees have been around much longer than that, and bees probably had color vision long before the appearance of flowers. In this evolutionary dance, the flower first courted the bee. The color of the flower is part of the invitation. Here, here, here, the flower hums. Come to me. Of course, flowers evolved to attract a variety of insects. With a visual range of ultraviolet to brilliant red, a butterfly sees color better than a bee, and better than you. Some moths see just as well as butterflies. Beetles are important pollinators, and the dung beetle can distinguish yellow, orange, and violet from blue, as well as yellow-green and light green. Most or all flies see in color. Tiny thrips, which feed on pollen, respond best to blue-green, blue, and yellow. Other insect pollinators include wasps, earwigs, cockroaches, book lice, grasshoppers, crickets, and lacewings. Researchers have yet to investigate their color sight. Many flowers are pollinated by birds, which have wonderful vision. Male and female starlings, with their black, iridescent plumage, look alike to us but very different to each other. The starlings are attracted to ultraviolet patterns not in our bird books. Like butterflies, birds can easily see red. In the Americas, red flowers are commonly visited by hummingbirds; in areas like central Europe, which do not have pollinating birds, red flowers are more rare. Mammals also pollinate plants. Nocturnal bats usually drink nectar from white or cream-colored flowers that stand out in the darkness. Many shrews, small marsupials, and rodents feed in twilight and prefer light colors. Nectar-rich flowers that attract mammals mainly through smell tend to be dingy or dull-colored, growing low to the ground. These kinds of patterns -- white for bats, red for birds -- are known as pollination syndromes. For a while, scientists thought that floral cues of color, scent, and form were a kind of crossword puzzle: all the cues formed a pollinator that was born hardwired to respond to a yellow marigold or a red skyrocket. The blue, sweet-smelling flower with a deep, narrow tube was cross-matched to a butterfly. A red, unscented, trumpetshaped flower was pollinated by hummingbirds. A greenish, skunky blossom attracted flies. Most scientists today play down the role of pollination syndromes and innate preference. Birds and bees and butterflies are just too flexible. They are selfish and pollinate the flower they like best, or the flower they can find, not the flower they were born to pollinate. They become field experienced. They respond to choice and chance. In one experiment, young swallowtail butterflies were presented with paper flowers in many different colors. They preferred yellow. Blue and purple came in second. Next, the researcher manipulated a certain wildflower, which has both yellow and magenta blossoms. She presented the butterflies with real yellow flowers without nectar and real magenta flowers with nectar. (To drain nectar from a flower, the researcher brought in advance teams of hungry butterflies. To make sure the flower was empty, she inserted tiny paper wicks into each tiny nectar tube.) Yellow remained a first choice. But after only ten flower visits, most butterflies switched to magenta. Now, these experienced butterflies were given a third choice: yellow flowers with nectar and magenta flowers without. They adapted again, quickly. The same thing happened with hummingbirds. Hummingbirds like red. But if I were to paint half the skyrockets in this meadow white, and remove nectar from the remaining skyrockets, the hummingbirds would decamp to white. Color as an invitation is too subtle. Color is an advertisement. Red is a billboard sign. Coke! Pepsi! Eat here! The product now has to live up to the hype. A few flowers rely on false advertisement. Their color or scent promises a reward that is never given. These flowers do depend on hard-wiring, the innate preference of newly hatched customers. Some good mimics can even fool a pollinator over and over. Flowers bobble. Flowers glow. Flowers shout. Come to me. Come to me. Come to me. *** SCIENTISTS WHO STUDY FLOWERS actually find themselves painting the petals of a red skyrocket white. They use an acrylic that they claim does not hurt the flower or affect the pollinator. Then they stand back and watch. What will visit the flower now? Flowers have also tried changing colors, in their own experiments, with good results. A flower may change color as soon as it is fertilized, or it may change automatically with age, when it is most likely to have been fertilized. The new color tells a pollinator that its services are no longer required. The bee can go elsewhere, preferably to a flower on the same plant or inflorescence. A more obvious strategy might be to have the flower drop off and die. But if reproductive changes are still taking place, parts of the flower may still be required. A post-change flower can also be useful to a plant that has flowers not yet fertilized. The large floral display continues to attract pollinators from a distance. Color change is surprisingly common and surprisingly unpredictable. Within a family, it can occur in some genera and not in others. Within a genus, it can occur in some species and not in others. Within a species, it can occur in some individuals and not in others. The mechanism of change varies. A young flower (Bauhinia monandra) from the West Indies is white, with a large, red spot in the middle of the central petal. As the flower ages, the central petal curls back and covers the red spot. Meanwhile, the four side petals turn pale pink. Now the entire flower looks pink. It is a strong signal: I'm old. Don't touch my stigma. In the same genus, the appearance of a pigment causes a yellow flower to turn red. The disappearance of a pigment causes a white flower to lose its ring of yellow. Changes in a flower's pH can also affect color, turning pink flowers blue and blue flowers pink. Flowers pollinated by night-flying moths or bats often change from white and cream to dull red, gold, or purple. Receding into the darkness, the post-change flower may still produce scent, helping attract visitors to other flowers on the plant. The banner petal on a white lupine is now purple. A field of white lilies is pink and red the next morning. A yellow blossom is no longer yellow. Messages are being sent, information exchanged. The code is in color. The colors are fleeting. WE WALK THROUGH A FIELD of wildflowers and we love the yellow cinquefoil even though it is really foog and we love the poppy even though it is ultraviolet. We are blind voyeurs. We have been invited to a party, and it doesn't seem to matter that we fail to recognize the host or many of the guests, that we stumble about awkwardly, not knowing what we are not seeing. Our hearts are gladdened. We know what we feel. Flowers make us happy.
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