To demonstrate how he develops an idea, Mr. Ellena digs into his pocket and pulls out a small, curved piece of wood. "Fifteen years ago, I came across this marvelous massoia wood, not well known in perfumery and used in Indonesian cuisine. The odor is startling, unforgettable, mysterious, a sensual riot of exotic spices, fruit and milky coconut. It's what I call a horizontal scent," he says. "It's round, supple, almost carnal, lascivious—in a word, feminine."