A British law requiring genetically modified foods to be labeled as such — in restaurants and bakeries as well as supermarkets — has caused manufacturers, retailers, and restaurant chains to make a mad dash to rid their goods of GM ingredients. But the law is also causing a fair amount of confusion, because different companies have different ideas about what “genetically modified” means and how it should be indicated on labels, and because additives and flavorings are exempt from the rules. Meanwhile, Monsanto, one of the biggest producers of GM seeds and technology, has been forced by public distrust and even anger to back off from its aggressive marketing. The company’s stock has lost more than a third of its value in the last 14 months, and analysts believe that unless things turn around fast, Monsanto may be forced to make radical changes, possibly dividing the company into separate pieces.