The mechanism of the Citrus pollen-tube growth into style and ovary, fertilization and development of embryo were studied. The results obtained were summarized as follows:
1. The pollen tubes of Natsudaidai grew faster than Satsuma orange in pistil of Natsudaidai or Satsuma orange.
2. The fertilization took place about 8 days in selfed Natsudaidai, 12 days in the crossing of Satsuma orange with Natsudaidai, and 14 days in self-pollination of Satsuma orange after pollination, respectively.
3. The fertilized eggs and nucellar cells began to divide 40 to 50 days after pollination both in selfed Natsudaidai and crossed Satsuma orange with Natsudaidai.
4. In Natsudaidai, embryo development was very slow and reached the globular stage 58 days, heart-shape embryo stage 72 days, and the complete embryo stage 120 days after self-pollination.
5. The nucellar cells of one to three layers near the micropylar of embryo sac and the region of the micropylar end to one-third of embryo sac have the ability to form nucellar embryos.