I believe the answer is the osteoblasts cells. These are bone forming cells that synthesize the organic matter of the matrix and help the organic matter of the matrix and help mineralize the bone. They line up in rows in the endosteum and inner layer of periosteum on the bone surface. Osteoblasts are non-mitotic, so the only source of new osteoblasts is the osteogenic cells. Stress and fractures stimulate accelerated mitosis of these cells and a rapid rise in the number of osteoblasts, which hen reinforce or rebuild the bone.