Repetitive production of leaf-derived embryos and secondary embryogenesis: Excised leaf-derived embryogenic masses were used to test the effect of TDZ on somatic embryogenesis and secondary embryogenesis (Table 2). In light, the masses turned brown and became necrotic after 45 d of culture on the hormone-free medium. In the presence of TDZ (0.01, 0.1, 1 and 3 mg dm-3), somatic embryos were induced from the leaf-derived masses after one month of culture (Table 2, Fig. 1D). The embryos developed into protocorms and some of them formed secondary embryos on the same TDZ-containing media (Fig. 1E). The numbers of embryos could be repetitive increased by subdivision of the embryo clusters. TDZ at 3 mg dm-3 resulted in a best response on the proliferation rate of fresh mass (5.4) and the mean number of embryos per explant (13.8) (Table 2, Fig. 1D). embryos/protocorms were transferred onto hormone-free medium and kept under a 16-h photoperiod. Under this condition, protocorms continued developing and further formed shoot (Fig. 1F). Plantlets were obtained after 6 - 8 weeks of culture (Fig. 1G). After subculturing every 6 weeks for three times, the plantlets developed 5 - 6 leaves and 3 - 4 roots. These plants were potted in sphagnum moss for acclimatization in greenhouse. After 6 months, the plants performed normal and the survival rate was 100 %. There were no obvious differences in morphology between TDZ-induced and TDZ + NAA-induced plants.