Hugo de Vries's mutation theory is now little more than a footnote to the history of biology, a failed theory that briefly led a few biologists astray. However, for the first quarter of the twentieth century it attracted considerable attention from both professional biologists and laypeople. De Vries's theory--together with the plant, Oenothera lamarckiana, that had supplied most of his evidence--became the focus of a surprising variety of imaginative hopes. Scientists and their various publics were fascinated by the utopian possibilities that the primrose seemed to offer, and their discussions shaped a public culture around biology that would help define the twentieth century as the "century of the gene." From a conventional history of science perspective (which, in the case of twentieth-century biology, often remains focused on the content of scientific theories and the professional communities that shaped them), the mutation theory seems unimportant. However, while De Vries's new theory of evolution ultimately failed to persuade the scientific community, it was much more important than is now realized, particularly because it helped make biology part of a wide variety of public debates. Understanding the mutation theory's story more fully suggests that we may need to rethink much of the rest of the century of the gene's history, to think less in terms of what happened in the lab and more about how biology came to function as public culture.