Excised roots of the bracken fern (Pteridium aquilinum (L.) Kuhn) have been continuously subcultured in various growth supporting media. The formation of gametophytes on the roots (apospory) occurs in three instances: on intact sporelings in culture, in aged growing root cultures after growth of the roots has ceased, and at an earlier time on excised roots in media lacking carbohydrates. Cells in the outer layers of the root tip become intensely green and form protuberant outgrowths which develop as diploid gametophytes. Addition of ammonium ions, an organic nitrogen source, or kinetin to the culture medium enhances the response.