Distant cross-breeding of tree peony is the main means of cultivar improvement at present and for quite a long time in the future, however, long breeding period and cross abortion are the two main obstacles for obtaining new cultivars effectively. The use of some assistant methods such as ovule, embryo and embryoid (somatic embryo) in vitro culture will be very important for an effective program in peony breeding. In this thesis, distant crosses of peonies, the cross abortion and the assistant methods prese...