Fig. 6.3-8. Longitudinal section through root of cattail (Typha). Regular rows of cells are especially easy to see here. The word "rib" in pith-rib meristem refers to rows of cells in which all the cells have been produced by orderly transverse divisions of a single cell. Notice that the three central rows have a slight kink in them (between the arrows); almost certainly the three central rows represent the products of six initial cells, not just three. The kink represents the area where the original three upper cells contacted the original three lower cells.