LILACS WERE THE FIRST trees I planted when we moved into our house. I love their heady scent, especially after a rain, and when they're blooming I can't pass by without burying my face in their petals. I cultivate many plants for their fragrances: lily of the valley, oriental lilies, mock-orange, roses, and a marvellous old iris that smells like grape candy. Although many of our experiences are intertwined with odours, we seldom consider their influence unless they are extraordinarily good or bad. In spring, after a long winter without "green" smells, we greedily await the fragrance of freshly cut grass and the rich, brown aroma of warming soil. "Smells like spring," we exclaim between deep inhalations. Humans can distinguish more than 10,000 odours ranging from sweet peas to sauerkraut. About 90 percent of what we consider flavours actually derive from our sense of smell. Try eating a piece of chocolate while holding your nose to see what I mean. We perceive pheromones exuded by other humans as scents and they influence our relationships. We incorporate smells into the mental maps of our surroundings: the green, citrus scent of sun-warmed Labrador tea on the tundra; the clear pine and wood smoke of the mountains; the alluring yeastiness of a bakery or brewery; the urban odour of gasoline fumes. Aromas even offer clues about unseen events. Sometimes, catching a waft of skunkiness in the backyard, I know that a red fox has visited during the night. Other animals have much better noses than we do. A polar bear can smell a seal more than 30 kilometres away. Some shark species can detect blood in seawater at a concentration equivalent to a drop of blood in a 150-litre barrel of water. The domestic cat has an olfactory membrane more than four times the size of a human's. A dog's sense of smell is outstanding. The bloodhound, known as a nose with legs, has some 230 million scent receptors - 40 times more than a human has. The next time you see a dog and its person together, imagine how differently they experience their surroundings. Scientists tell us the nerves involved in perceiving scents are linked to the brain's emotional centre. Perhaps that's why we are rarely ambivalent about scents: either we like them or dislike them. The same odour may affect people differently. I love the smell of horses, but my husband claims they stink. The connection with our emotions may explain how certain smells can whisk our thoughts to distant places and times. Chlorine makes me remember lying on rough, warm concrete beside the community pool, shivering as a breeze blew over my wet skin. Freshly cut hay brings memories of throwing bales onto a flatbed trailer. A certain soap, along with insect repellant, reminds me of my summer in a camp near the Arctic Circle. A whiff of Tabu perfume conjures a vision of my mother, dressed up in her favourite colour, red, for a rare evening out. Knowing a bit about the science of scents makes me re-evaluate everyday activities. When I stop and smell the roses, the compost, the spearmint, the tomatoes, or the sun-dried laundry, I'm not dawdling at my chores. I'm gathering memories. - REBECCA L. GRAMBO