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.