The majority of plants produce both male and female flowers. Some 5% of plants, however, have separate male and female individuals, a condition known as "dioecy". Dioecy shows up in all sorts of unrelated species, raising the possibility that there is some underlying mechanism common to these independent evolutionary transitions from hermaphroditism to dioecy. Several explanations have been offered. What is lacking is information from natural populations concerning whether any of these explanations actually apply. That is the target of this project. Dr. Muenchow has identified a situation in the genus Sagittaria where, among a set of near relatives, she finds both hermaphrodites and dioecious plants. This allows her to compare the two forms under very similar field conditions, and to determine whether the ecological conditions that the various hypotheses assume actually seem to apply to this genus. The work is important to developing an understanding of evolutionary processes. In this particular case, theoretical development has outstripped experimental evidence. The experiment evidence this project provides will, therefore, rapidly influence further theoretical work and form an integral part of an ongoing scientific "discussion".