The promeristem can be defined as that part of the root apex which is capable of giving rise to all the tissues of the root. In the roots of vascular cryptogams, for example, the promeristem would consist of the apocal cell only, and in flowering plants it would comprise the initials of the histogens. There is thus a tendenccy to regard the promeristem as a rather small region, situated terminally in the root apical meristem, below the root cap. A growing body of modern work, however, suggests that in many roots the promeristem is broad and consists of a somewhat cup-shaped group ofcells an the periphery of a central inactive region.