The cucurbit family is remarkable for its diversity of sex types. Hermaphroditism is rare among the Cucurbitaceae; monoecy and dioecy are common, and different stages in the presumed evolution of sex-determination mechanisms can be found, from single sex genes (e.g. in cucumber and melon) to heteromorphic sex chromosomes (e.g. in Coccinia grandis; Roy and Saran, 1990). Cucumis sativus, the cucumber, an important vegetable crop, is undoubtedly the cucurbit species in which plant sex expression has been studied most extensively.