[en] Effects of ¹³¹I applied to the inflorescence on the induction of somatic mutations in Tradescantia stamen hairs were previously investigated, and the doubling dose (activity) was estimated to be 4 nCi. In the present paper, the absorbed dose rate in stamen hairs of Tradescantia for β rays from the applied ¹³¹I was calculated. The doubling dose for the ¹³¹I (4 nCi) applied to the inflorescence was estimated to be higher than 0.3 rad (assuming uniform distribution of ¹³¹I on the surface of the buds and assuming that the shape of the buds was a sphere) and lower than 1.0 rad