Maturing seeds were collected from fifty-year-old trees of Fraxinus mandshurica. The cotyledon and hypocotyl zygotic embryos were excised and cultured on 1/2MS media to induce somatic embryos. In cytological study of embryo development, by the way of paraffin, somatic and zygotic embryogenesis was observed and compared under light microscope. The results showed that somatic embryos from zygotic cotyledons originated directly from single epidermis cell. The somatic embryos that indirectly occurred on the embryogenic callus came from its singular surface cell or internal multi_cells. There was an obvious cytological difference between embryogenic and non-embryogenic callus. Somatic and zygotic embryogenesis underwent the similar course, passing through proembryo, heart, torpedo and cotyledonary stages. The important differences in morphogenetic process exited as following: volume of somatic embryos was smaller than its partner at the same development stage; somatic embryos had no obvious suspensors; somatic embryos showed morphologic variations.
