Scientists at Duke University Medical Center have unlocked another piece of the puzzle about how we identify particular odors:
In studies in mice, the researchers found that nerve cells in the brain's olfactory bulb -- the first stop for information from the nose -- do not perceive complex scent mixtures as single objects, such as the fragrance of a blooming rose. Instead, these nerve cells, or neurons, detect the host of chemical compounds that comprise a rose's perfume. Smarter sections of the brain's olfactory system then categorize and combine these compounds into a recognizable scent.
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Every spring I visit an “old friend” at Kubota Garden in Seattle: a stately Chinese plum tree. If I sit against its large trunk, I’m completely hidden from view by its flower-covered branches that touch the ground. The scent of the thousands of white plum blossoms changes over time. The tiny round unopened buds smell fresh and leafy with a whiff of rain. At their peak, the flowers diffuse a strange and lavish perfume with hints of honey, clove, old-fashioned bubblegum, wood smoke and masa. As the flowers fade and begin to fall, their last breath smells of delicate incense. 
