Abstract: An immature zygotic embryo of Torreya grandis‘Merrillii’was dark cultured for 45 days on an SH medium supplemented with 0.1 mg ? L-1 NAA，500 mg ? L-1 AC，3% sucrose and 0.5 g ? L-1 Gln to induce embryonic callus，which was watery，semi-transparent and slimy. Then the callus was transferred to SH media supplemented with 20 g ? L-1 PEG and 10 mg ? L-1ABA and dark cultured for three months for somatic embryogenesis. The morphological and cytohistological observation of somatic embryogenesis was performed by iodine-potassium iodide staining and Paraffin technology. Results showed that the embryonic callus originated from the symmetrical division of epidermal or cortical cells of hypocotyl. The callus consisted of two types of cells，viz. small-sized circular cells with dense cytoplasm and highly elongated vacuolate cells. The two types of cells formed proembryonic masses（PEMs）expressed as PEM Ⅰ，PEMⅡ，and PEM Ⅲ and some free cells. The PEM Ⅲ cultured in the basic medium without hormones added developed to form a proembryo，which was then transferred to mature media to form a cotyledon embryo by being subjected to globular，rodlike，heart-shaped，and torpedo-shaped development. after transferred to SH media，the cotyledon embryo developed to form an intact plantlet through elongated radicle and growth of needles from germ. In vitro culture of polyembryony originating from division of degraded suspensor of a zygotic embryo could also produce idiosome. Development of primary somatic embryos was often accompanied by the formation of secondary somatic embryos.

Key words: Torreya grandis‘Merrillii’, somatic embryogenesis, origin, development, morphology；cytology