Nuclear volumes and cell areas were determined for seven regions of the meristem of roots of Zea mays. Roots were fixed in 10 per cent neutral buffered formalin, in 3 per cent glutaraldehyde or in acetic acid/alcohol; they were prepared as sections or alls were teased apart. Mean volumes of interphase nuclei were similar in all regions of the root except the vascular tissue of the stele. Mean nuclear volumes and the overall range of volumes were similar in sub-populations of cells with different proportions of G1, S and G2 cells, e.g. in row I of root cap initials, whose cells lack a G1 phase, and in quiescent centre cells, which are mainly in G1. Nuclear volume does not appear to be closely correlated with DNA content. Nuclear volumes covered a 6 to 12-fold range within a meristem and even within specific regions, in which cells are part of the same cell lineages, there was a 4- to 9-fold range. Nuclear volumes were compared in sister cells in rows I and II of the root cap initials. In 10 per cent of the pairs, sister nuclei had identical volumes; the other pain had different volumes and mean difference was 68 μm3. Mechanisms by which this variability could be generated are discussed, particularly asymmetry, at mitoses, of factors that regulate nuclear growth.