Various kinds of free radicals were measured at room temperature by the ESR spectrum method after seeds of rice
soybean
maize and green gram were irradiated with nitrogen ions. The g values of free radicals were calculated and the stability of free radicals was observed. Experimental results show that the free radical concentration in seeds increases with ion dose and gradually reaches to a saturated value; irradiation damages of seeds increase with ion dose;the free radical concentration decreases with the increase of moisture content in seeds; and free radicals in seeds decrease very slowly. The relation between free radicals and damages in seeds was discussed.