A patent on a means to produce seeds which germinate, but which produce plants whose seeds are sterile, was reviewed in Science, p 850, 30 Oct 98 vol 282. The trick is that the seeds are genetically engineered, and the seeds are 'activated' by an antibiotic (which acts like a signal). The purpose is to copy-protect other engineered genes in the organism. US pat 5,723,765 David Honig "When horsemeat is outlawed, only outlaws will eat horsemeat"