During cereal endosperm development, the triploid primary endosperm nucleus undergoes a series of mitotic divisions without cytokinesis, and the nuclei migrate to the periphery of the central cell, which also contains a large central vacuole (Figure 21.26, see parts A-D). As in the Arabidopsis coenocyte, each of nuclei is surrounded by radially arranged microtubules (see Figure 21.26E). Anticlinal walls form initially between adjacent nuclei, resulting in the tubelike alveolar cells, with the open end pointing toward the central vacuole (see Figure 21.26F). (...) The innermost layer of daughter cells remains alveolar in structure, and continues to divide periclinally until cellularization is complete (see Figure 21.26G and H). The most important source of starchy endosperm cells is the interior cells of the cell files that are present at the completion of endosperm cellularization (see Figure 21.26H).
"Plant Physiology and Development" int'l 6e - Taiz, L., Zeiger, E., Møller, I.M., Murphy, A.