Why do cut flowers smell so bad?

A reader asks: “I've noticed that after flowers have been picked, they start smelling differently. For a long time I thought roses at the store smelled horrible. Then I noticed that the lilacs I pick will start smelling the same way a couple of days after I pick them. They change to the wonderful smell of lilacs to a horrible stench. Do flowers give off a death pheromone? Thanks.”
This is an interesting question, and the Phactor is uncertain he knows the answer. Floral scents are complex, and they often wane after being picked, and the most likely reason is simply they do not have as much water in their xylem stream, water under as much push-pull force to create as much scent after being cut. However, the transformation you describe from lovely to horrible stench is not something personally experienced. But no, there is no “death pheromone”, although decomposition does smell bad, and the cut end of bouquets can get pretty “ripe”. Perhaps some of my knowledgeable readers can suggest some alternatives.