Delphinidin

Cells in the region of cell division, which is composed of an apical meristem (a tissue of actively dividing cells) in the center of the root tip, produce the surrounding root cap. Most of the cell divisions take place next to the root cap at the edges of this inverted cup-shaped zone, located a short distance behind the actual base of the meristem. Here the cells divide every 12 to 36 hours, while at the base of the meristem, they may divide only once in every 200 to 500 hours. The divisions are often rhythmic, reaching a peak once or twice each day, usually toward noon and midnight, with relatively quiescent intermediate periods. Cells in this region are mostly cubical, with relatively large, more or less centrally located nuclei and a few very small vacuoles.

In both roots and stems, the apical meristem soon subdivides into three meristematic areas:
1. The protoderm gives rise to an outer layer of cells, the epidermis;
2. The ground meristem, to the inside of the protoderm, produces parenchyma cells of the cortex;
3. The procambium, which appears as a solid cylinder in the center of the root, produces primary xylem and primary phloem.

Pith (parenchyma) tissue, which originates from the ground meristem, is generally present in stems but is absent in most dicot roots. Grass roots and those of most other monocots, however, do have pith tissue.