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.