Abstract:The relationship between the seed coat and the seed dormancy of korean pine (Pinus koraiensis) is discussed in this paper. The germination percentage of seeds with their coats broken, is very low. It showed that the mechanical obstruction of the hard seed coat is not the major cause of the seed dormancy. The experiments with embryos cultured in vitro and treated with exogenous ABA or germination test of seeds soaked by ABA solutions show that ABA is not the major cause of the seed dormancy either. Respiratory patterns of the intact seeds and of those with their testa or both removing testa and inner coat were studied. It is indicated that removing both of testa and inner coat greatly enhanced the oxygen uptake. Obviously, the impermeability of oxygen through the seed coat is, therefore, the major external cause of the seed dormancy.