Pheromonal interactions between cordate gametophytes of the lady fern, Athyrium filix-femina, were investigated using a protocol typically used for detecting water-soluble pheromones such as antheridiogen. Three week-old, cordate gametophytes were transferred to agar containing abstracts from a previous generation of gametophytes (treatment) and to fresh nutrient agar (control). Three weeks after transfer, gametophytes were examined from treatment and control plates. Each gametophyte was measured for size (area) and shape (circularity), and scored for number of antheridia and archegonia. Treatment gametophytes were significantly smaller, less circular, had fewer archegonia, and possessed antheridia more often, than control gametophytes, a pattern consistent with known antheridiogen effects on gametophytes of transitional morphology and sensitivity. The experiment was repeated using gametophytes that were six weeks old at time of transfer. Treatment gametophytes in the second experiment did not differ in size, but were significantly more circular and possessed fewer archegonia, than control gametophytes. The second experiment revealed phytochemical interactions between cordate gametophytes. The contradictory effects of increased circularity without increased size may be due to one or more phytochemicals that accelerate anticlinal divisions in the meristem resulting in increasing circularity, at the expense of oblique or periclinal divisions that contributed to size. Likewise, the decreased production of archegonia, which can not be attributed to production of antheridia, may be a consequence of a reduced rate of oblique and periclinal divisions in the meristem, from which archegonia are ultimately derived. Antheridiogen, a water-soluble pheromone with structural affinity to gibberellins and that induces maleness in acordate gametophytes may be involved, since its production is closely associated with attainment of a cordate morphology.

Key words: development, fern gametophyte, pheromone