Abstract
Files of metaxylem were traced to their levels of origin in the root apex of Zea mays. The 1st 4 files differentiated simultaneously, with new files added sequentially at more proximal levels in the root. The differentiation of the metaxylem was correlated with dimensions of the quiescent center. From these correlations a hypothesis is advanced of the possible regulatory effects of the quiescent center on primary vascular tissue patterns in roots.