Farmers better be careful whose seeds they plant. The Supreme Court ruled unanimously in favor of Monsanto in its suit against an Indiana farmer who planted its genetically modified seeds without paying the company. The case has been closely watched for its bearing on companies that hold patents on DNA molecules and other self-replicating products, but Justice Elena Kagan stressed that the court was ruling narrowly, addressing only the farmer’s violation of patent law. The farmer first bought seeds for a crop of soybeans that had been engineered to be resistant to the pesticide Roundup, which is also a Monsanto product. But for his second crop, he took a mix of seeds from a grain elevator, sprayed them with Roundup, and planted seeds from the plants that survived, exploiting what he believed to be a loophole in the contract.