Numbers, n, of eLTRC estimated from combinations of various volumes of bone marrow in mice receiving radiation doses between 3.0 to 7.0 Gy. Regression lines were fitted by the methods of least squares. Number of eLTRC in the whole marrow volume was estimated by extrapolation to 100%. The five data points exceeding n = 3 in the 3.5-Gy graph are not shown.