AUTECOLOGICAL STUDIES ON AUDOUINIA-CAPITATA (BRUNIACEAE) .5. SEED DEVELOPMENT, ABORTION AND PRE-EMERGENT REPRODUCTIVE SUCCESS

Ovule development, megasporogenesis, megagametogenesis, embryogenesis, endosperm development and seed germination of Audouinia capitata are described. In sharp contrast to the relatively high incidence of abort ion and non-viability of microspores demonstrated previously, no pre-a nthesis aberrations occur in the megagametophyte. In many fertilized o vules the primary endosperm nuclei remain undivided, enlarge considera bly for up to five weeks and eventually degenerate, accompanied by abo rtion of the zygote. A low incidence of abortion is evident after the fifth week. Abortions after 11 weeks of development are identifiable i n mature fruits. A substantial number of mature seeds are devoid of, o r contain low densities of, protein bodies. After germination, the rad icles of these seeds stop growing soon after emergence from the fruits . It is suggested that abortion is regulated by inter-ovular competiti on for available nutrients, or by a strongly fixed, genetically contro lled system. This strategy could have been selected to allow for the e conomization of reserves in the 6-ovuled, indehiscent ovaries that act as dispersal units. Possible explanations are suggested for abortion rates in excess of those implied by a fixed general system of one seed per indehiscent fruit. When accepting a seed:ovule ratio of 1:6 as fu ll realization of the seed-setting potential, and ignoring all nonsexu al factors, the pre-emergent reproductive success is only 9%. This def iciency is a contributing factor in the rarity of the species.