Genetic analyses, particularly in Arabidopsis, have led to the identif
ication of mutants that define different steps of ovule ontogeny, poll
en stigma interaction, pollen tube growth, and fertilization. isolatio
n of the genes defined by these mutations promises to lead to a molecu
lar understanding of these processes. Mutants have also been obtained
in which processes that are normally triggered by fertilization, such
as endosperm formation and initiation of seed development, occur witho
ut fertilization. These mutants may illuminate apomixis, a process of
seed development without fertilization extant in many plants.