Floral Biology and Self-Incompatibility in Linum

Species of Linum are distylous and self-incompatible or homostylous and self-compatible. The period of maximum stigma receptivity in L. grandiflorum was ascertained from seed-set data and was used to study pollen/stigma interactions in intra- and interspecific combinations. Measurements of the osmotic pressure (OP) of stigmatic cells of several Linum species showed interspecific variation. Many distylous species showed differences in stigmatic OP between pin and thrum morphs. Interspecific crosses show that the pollen/stigma compatibility of the cross cannot be predicted on the basis of similarity or difference in stigmatic OP. The results cast doubt on the role of OP differences in the control of heteromorphic self-incompatibility in Linum.