The history of perfume is as old as antiquity. It has invoked our ancient gods, given us sweet identity, and sent us embalmed to the grave. The prophet Mohammed said "perfume is the nourishment that stimulates my thinking". The sense of smell - which also distinguishes flavour - is our strongest memory trigger, sending Proust off on volumes from the mere tasting of a Madeleine cake.

Thinking with your Nose is the current exhibition at London's historic Chelsea Physic Garden. With recently established borders of plants used in the industry of fragrance, flavour and aromatherapy, inspired by the plant collection on the roof of the perfume museum in Grasse, the exhibition tells the history of perfume and its methods of extraction. Grasse is still the centre of France's perfume industry, wafting with the scented airs of manufacturers such as Galimard and Fragonard, who recently brought out a limited edition scent based on Suskind's grotesquely inventive novel Perfume. The "nose" in Perfume is a certain Jean Baptiste Grenouille, whose ultimate creation was the perfume of young virgins. How he obtained it I won't divulge, but he has a living namesake in Yorkshireman Dr Peter Wilde (known as Mr Frog) whose invention for extracting plant oils and their scent is also on display at Chelsea. His inspiration was a tasteless cup of British Rail coffee. Saying to himself "If I can't do better than that, I deserve to starve" he promptly went into the coffee business, which started him on a quest over many years for its elusive scent. With the gas 1112 Tetraflourethane (used in the refrigeration business) he found he could obtain an exceedingly pure plant oil without destroying the plant's "essence".

Dr Wilde has since captured not only the essence of old English roses (presented in soap form to Britain's best old English rose, the Queen Mum) but also chocolate, which is sold to the confectionery business, and many plant extracts for the pharmaceutical industry. Though he extracts natural oils, he acknowledges that most perfumes are synthetically produced today. Chanel No 5 was the first to use synthesized aldehydes (a family like acids or alkalines) as far back as 1921. Might some perfumes also contain hidden ingredients, such as pheromones, which are mostly odourless to humans but with a secret message of sexual attraction? "Almost certainly" says Wilde, "you can extract them from horse sweat. Why do you think little girls play with horses?"

But more than in hidden mating molecules or notes of citrus, flower, fougere, chypre, wood, amber or leather (the seven fragrance families classified by the Comite Francais du Parfum) the essence of a scent lies in our memories. Perfume evokes both memory and desire. In one of the greenhouses at the Physic Garden there's a plant Osmanthus Fragrans, whose flowers smell profoundly of apricots. "Bukra al al mish mish" as the Arab saying goes: "Tomorrow in the apricots". What does it mean? Eternity? Joy? Obsession? Allure? It's on the tip of my nose.