Evidence of dichogamy in Santalum album L.

Flowering, fruit set, embryological development, and pollination trials were investigated in Santalum album L. Each ovary may have three to four ovules. Microsporogenesis and megasporogenesis in the same flower were synchronized at the earlier stages of flower development. However, at anthesis, when pollen was mature, the magaspore had developed only to the stage of a one- to two-nucleus embryo sac. As the eight-nucleus embryo sac developed, some mamelon cells began to undergo programmed cell death, forming holes into which the eight-nucleus embryo sacs extended, becoming "N" or "S" shaped. The development from a two-nucleus embryo sac to a matured eight-nucleus embryo sac lasted up to 10 d. Fruit-set from open pollination was less than 2%. The endosperm develops prior to division of the zygotic embryo and one to three embryos and endosperms were formed in the same fruit. A mature seed usually germinates to produce one seedling; however, two and three seedlings from one seed were also observed, albeit at a low frequency. Pollination trials showed that no seed sets when inflorescences were covered with a bag; however, artificial pollination could improve fruit set. Our pollination trials and embryological studies proved that the flower of S. album is dichogamous and fruit set has high heterozygosity.