The Effect of Partial Self-fertilization on Type Frequencies in Heterostylous Plants

A population of heterostylous plants is studied mathematically under the assumption that a small amount of self-fertilization is possible. The frequencies of the incompatibility types are determined as expressions involving the probabilities of self-fertilization. A comparison is made with observed frequencies of the Long, Mid and Short types in Lythrum salicaria, and it is concluded that the differences between the type frequencies seem to be too large to be accounted for by unequal probabilities of self-fertilization.