Gemmae: a role in sexual reproduction in the fern genus vittaria.

Gemmae are generally defined as vegetative propagules. In the shoestring ferns, Vittaria, gemmae grown in the presence of mature gametophyte plants or on medium containing gibberellic acid produce antheridia in lieu of vegetative growth. This suggests that antheridial differentiation in Vittaria is controlled by a chemical antheridogen system similar to those described in other fern genera. In natural populations of Vittaria gametophytes composed primarily of long-lived individuals, gemmae may provide the only source of tissue susceptible to antheridogen action and may have evolved in response to that condition.