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ANATOMY OF A ROSE -- EXPLORING THE SECRET LIFE OF FLOWERS |
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THREE: Smelling Like a Rose IN THE AISLES OF EVERY DEPARTMENT STORE are products that use the brand names of rose, orchid, violet, honeysuckle, magnolia, narcissus, orange blossom, carnation, and hyacinth. We use these scents in our soaps and perfumes, bubble baths, lotions, shampoos, deodorants, and even air fresheners and cleaning products. We want to smell like flowers. We are no different from most cultures, ancient and modern. The Hindus and Egyptians worshiped their gods with fragrance. The Greeks specialized in perfumery. The Bible reeks of incense. Europeans thought eau de cologne could ward off the plague. Aztec noblemen carried fresh flower bouquets. In all of human history, there is hardly a time or place that does not reflect our preoccupation with smelling good. Most perfume today has three odor groups, or notes. The top note comes first, with a floral highlight such as lilac or lily. The middle note provides body and uses the essential oils in jasmine, lavender, or geranium. The third, or base note, includes animal products, such as musk from rutting deer or the pasty fluid from the anal glands of civet cats. These last products also add the intangible qualities of body and warmth. The human body has its own array of scent from glands scattered on the face, scalp, breasts, under the arms, and in the genital area. Oddly, humans are desensitized to this last smell. Long ago we suppressed our ability to sniff out ovulation. One theory suggests that when we began living in complex social groups, smells of sexual readiness threatened the pair bonding needed to raise children. Frankly, culturally, we are a bit disgusted by our own odor. We do not want to smell too human. But we do want to smell like something. And we want to attract mates. So the top notes of perfume are from flowers that use scent to attract pollinators. The middle notes are oils and resins that resemble sex steroids. The base notes, at low concentrations, are obvious. We don't want to overstate our case. We don't want to smell too much like a deer or civet cat. We want to smell like a rose. We want to smell like orange blossoms. We want to smell like jasmine. On their part, most flowers want to smell like food. Some flowers want to smell like a rotting corpse. Some flowers want to smell like excrement. Some flowers want to smell like fungi. Flowers have their own agenda. A SINGLE FLOWER CAN produce as many as a hundred chemical compounds, with smells mixing and combining in patterns that change over time, with parts of a flower smelling differently from other parts, with smells sending out a variety of signals: Lay your eggs here, nectar over there, eat now. In large quantities, the chemicals that produce scent are often toxic. To protect the plant, they are stored as volatiles (oils that convert easily from a liquid to a vapor) in special cells, usually in the flower itself. The petal tissue might manufacture some of these volatiles; the reproductive organs may be responsible for others. The vegetative tissue of the plant also adds to a flower's fragrance, which is usually a blend of many odors. Odor molecules are released through the process of evaporation. Once in the air, the molecules begin to move about randomly, farther apart from each other, until they are carried away from their source by the wind. For a while, however, there is a coherent trail of molecules, known as an odor plume. This plume has a destination. More often than not, it is meant to intersect an insect's antenna, which has hundreds of cells designed to catch it. The outline area of the antenna is the insect's nostril. In some moths this can be as large as a small dog's. A dog sniffs to breathe in smell. An insect waves its antenna. Entering a plume, insects tend to zigzag, casting down or to the side when the odor is lost. When a zigzagging insect gets close enough to actually see a flower, it may suddenly ''beeline'' to its destination. Flowers smell so good because insects smell so well. Some moths can detect a scent a mile away. Most moths, like poodles, smell just about everything. Other pollinators, especially bees, also distinguish and remember odor. In response, flowers may have evolved a complex mix of smells, and this may encourage what botanists call flower constancy. Flower constancy is the "loyalty" of a pollinator to a specific flower or species. First, a flower species "wants" to smell and look different from competing species. Second, a flower wants to attract a pollinator that will recognize and remember the difference. Finally, a flower wants that pollinator to be loyal, flying off with a load of pollen to fertilize a compatible flower. For their own reasons, insects seem to oblige. Even when other flowers are blooming, a bee may continue to visit the familiar red clover or pink four-o'clock. The flower gets fertilized by a similar flower, and the bee becomes adept at handling that species. Because a honeybee might visit five hundred flowers in one foraging trip, any savings in energy or time adds up quickly. We choose the same strategy when we shop, every day, at the same grocery store or drive the same route to work. Because different flowers open and release their scent at different times, an insect can have many loyalties. The blue chicory has nectar in the morning. Red clover is best after lunch. The four-o'clock opens in late afternoon. The evening primrose follows the four-o'clock. A honeybee's memory for odor is linked to a certain time of day. Typically, bees seem to "trapline" a series of flowers, moving to each appropriate one at the appropriate hour, and then heading straight for home. The timing of scent production is part of a flower's reproductive success. Some flowers, like roses and clover, are scented only in the day. Some flowers are scented only at night. There are smells that you and I will never know, because we are not nocturnal. There are smells like maps to the country of loyalty. *** EVERY YEAR, worldwide agriculture produces over 100 million tons of cane and beet sugar. The Australians, Irish, and Danish eat one hundred pounds of refined sugar per person per year. Americans eat a little less. Nectar is mainly sugar water, sometimes containing sucrose or cane sugar, sometimes a mix of sucrose, fructose, and glucose. Most of us understand the butterfly. We would also extend our mouthpart, automatically, at the equivalent of a candy bar. In concealed nectaries or in open pockets, nectar is the pollinator's reward. In different species, nectar can be secreted by almost any part of the flower. Nectar-rich flowers often have a strong, sweet fragrance that does not necessarily come from the nectar. (Bird-pollinated flowers also provide nectar and are relatively unscented because birds do not have a good sense of smell.) The flower's strong perfume is first a lure, a dinner bell, and an advertisement. Up close, scent marks on the flower, like visual guide marks, may further direct an insect to the source of food. The subtle smell of nectar may help some bees determine if the flower is full or empty. Flower mites also use nectar to recognize their host species. Mites ride from flower to flower in the nostrils of the hummingbird; when they smell the right nectar, they gallop home down the bird's beak. *** IN SOME FLOWERS, pollen is the reward, and the odor of pollen is the primary scent. This is particularly true in plants visited by pollen-eating beetles. Bees, too, are good at smelling and distinguishing different pollen from different flowers. Perhaps the best image for the smell of pollen is the kind of breakfast only a farm worker should have: eggs, bacon, ham, cheese, potatoes, biscuits, and gravy. The steaming plate sends out a strong odor plume. *** POLLEN CAN ALSO BE SEXY. In the sunflower moth, when virgin females are exposed to the odor of pollen, they begin signaling for males earlier and spend more time signaling. Later, more of their eggs mature. This interplay of food, scent, and sex is a common theme. Some flowers smell like the sex pheromones of a butterfly; the male carpenter bee attracts females with a pheromone that smells like a flower-good enough to eat. (A chemical is considered a pheromone when it is used as communication between at least two members of a species.) Through millennia of mimicry and exploitation, flower volatiles and insect pheromones have co-evolved, with flowers imitating pheromones and pheromones imitating flowers. We want to smell like a rose. We want to smell like a butterfly. We want to smell like an insect pheromone. It doesn't stop there. A major ingredient in the sex pheromone of many moths is also found in the sex pheromone secreted in urine by female Indian elephants. The urine is meant to attract the attention of a bull -- the bigger the better. In one experiment, women who sniffed musk, the sex attractant of Himalayan deer, developed a shorter menstrual cycle, ovulated more often, and conceived more easily. The smell of musk resembles the smell of steroids found in human urine. The chemical structure of steroids like testosterone resembles plant resins like myrrh. We use these resins in our perfumes, just as we use the volatiles of flowers. The fact that so many things smell like each other is partially explained by nature's efficiency. A compound that works here will also work there. We all came from the same primordial soup. Poets, who equate one thing with another, often echo scientists. Similes are real. Metaphors are chemical. In the Bible's lyric poem the Song of Solomon, odor is the language of love: "My beloved is unto me as a bag of myrrh that lieth between my breasts. My beloved is unto me as a cluster of henna flowers in the vineyard of Engedi." The flowers of henna, lime, and chestnut smell like semen. Myrrh has a smell compared to the oils secreted by glands in the human scalp. *** WE WANT TO SMELL LIKE A ROSE. We want to smell like a henna flower. But we don't want to smell like the largest inflorescence in the world, the nine-foot-tall giant arum, mythically pollinated by elephants, which gives off a stench so revolting it has made men grow faint. We don't want to smell like the dead horse arum, a flower that evolved near gull colonies and came to resemble the rotting carcass of a bird. This arum is round and plate-sized, grayish purple, blotched with pink, and covered with dark red hairs, or trichomes. Its smell of decay draws blowflies, which come to feed and lay their eggs. The flies crawl into what appears to be an empty eye socket or an inviting anus, deep into the flower, where they are trapped, the exit closed by bristly hairs. Fed by nectar, the flies lay eggs that will later hatch and die for lack of food. Suddenly, the flower releases its pollen, which covers the blowflies. The bristly hairs wilt. The flies crawl out again. Other flowers pollinated by flies and beetles can smell variously like dead animals, rotting fish, or dung. Colors of red, purple, and brown add to the effect. Dark spots or warty areas look like clusters of insects already feeding. The common names of a plant tell the story: skunk cabbage, corpse flower, stinking goosefoot. We don't want to smell like a dead horse arum. But we do want to smell like jasmine, which also has a distinct fecal odor beneath the top notes of cloying sweetness. At very low levels, at levels that reach into childhood, at the level of the unconscious mind, at a level that defines our kinship with the rest of the world, urinary and fecal smells are commonly added to our best perfume. *** MOST FLOWERS SMELL like a restaurant. They use scent to signal an insect that they have food or to deceive an insect into believing that they have food. Some flowers smell like home, a good place to raise a family. A foogus gnat lays its eggs where the eggs can hatch and eat the fungus. Plants that mimic fungi grow low in the forest, with dark purple or brown flowers. Fleshy parts of the flower seem particularly to attract the fungus gnat. One orchid has a creamy, gill-like area that resembles, precisely, the underside of a mushroom. A few flowers are drag queens that advertise for sex and use scent as part of their costume. A Mediterranean orchid has an oval, convex lip that glistens metallic violet-blue. Its narrow, yellow border is fringed with reddish hairs. Dark red, threadlike upper petals move in the wind like an insect's antenna. The orchid looks and smells like a female wasp. When the male wasp lights and tries to copulate, pollen is transferred onto its head. Pseudocopulation is rare but not unique. Around the world, certain bees, wasps, and other insects are trying to mate with flowers that appear to be what they are not. (The bee fooled by a mere flower may be lucky. The larvae of blister beetles also lump together to look and perhaps smell like a female bee. These larvae first attach themselves to a male and then try to find their way into a young bee nursery, where they will feed on pollen.) Occasionally, a cigar is just a cigar. The boldest and most bizarre use of smell may be "perfume flowers," whose scent tells a male euglossine bee that this flower has ... scent. Like someone at a department store, shopping for a very important night, the bee mops up the perfumed liquid with feathery brushes on its front feet. The smell is stored in a pouch in a back leg and combined with other odors to create a private irresistible pheromone. *** SMELL IS A COME-HITHER. It can also be a go-away. Some fertilized flowers change their scent to signal pollinators to pollinate elsewhere. Many flowers stop producing scent altogether, the most definitive no. Pollinators use scent, too. Bees secrete a pheromone to mark recently visited flowers. The short-term odor is a memo to oneself: This flower is out of nectar. Other bees respond to the smell. No one wants to crawl up an empty corolla tube. *** THE MOST EXPENSIVE PERFUME in the world, Joy, mixes a little jasmine with lots of rose. Roses have always generated passion. The Romans celebrated the holiday Rosalia to excess. When the prophet Muhammad ascended to heaven, drops of his sweat fell to earth and turned into roses. The early Christian rosary had 165 dried and rolled-up rose petals. The smell of a rose is first absorbed by the mucous membranes in our nasal cavity. Next, receptor cells fire a message to the limbic system, an ancient part of our brain and the seat of emotion. Here, memories associated with smell decay more slowly than visual memories. We want to smell like a rose. Of course we do. Everything else is smelling like something. Molecules everywhere are drifting into the wind, jostling against each other, grabbed by a sensory cell, by the antennae of a moth, by a dog's nose, by a lover's inhalation. We want to be part of that movement. We want to move. We want to be moved.
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