Fig. 6.1-2b.
Magnification of basal meristem of a cactus spine (Morawetzia doelziana).
This is a very simple meristem and the spine it produces is also simple. The
spine body is just a mass of fibers produced by cells in the center of the
meristem; consequently the center of the basal meristem can be called a ground
meristem. Look carefully at the two edges of the basal meristem, those cells are
aligned in regular rows; there is actually a uniform outer layer that encloses
the rest of the meristem (the left edge and right edge are just two cuts through
the same cylindrical layer). This outer layer produces the cells that
differentiate into the spine epidermis (which is also sclerenchyma), so the
outer layer is a protoderm.