Fig. 4. Frequency and absolute number of (A) osteogenic, (B) adipogenic and (C) chondrogenic progenitors in hematopoietic sites through development. Osteogenic and adipogenic progenitor frequencies and numbers were determined based on the number of colonies displaying the appropriate phenotype. Chondrogenic progenitor frequency and number was determined based on the number of cartilage foci after 21 days of aggregate culture. Data are expressed as mean±s.d. (n=3 to six independent experiments). Absolute number determinations in the neonatal and adult BM used the following values: newborn BM, 9.8 x10⁷ cells; adult BM, 30.0 x10⁷ cells (Harrison, 1993). These values were extrapolated from those of Stewart et al. (Stewart et al., 1993).