The genesis of bone, the palimpsest of the evolution of man, remains to this day undetermined and a subject of much controversy. This controversy involves not only the fundamental problems of the chemical processes of ossification but also its histogenesis. Without established knowledge of the rôle (if any) played by tissue cells in the laying down of bone and of the specialization required of cells for such a function, the part played by such tissues as the periosteum, endosteum, cartilage and granulation tissue can only be conjectured. However, I have presented experimental results which indicate that the periosteum is particularly conducive to the deposition of new bone on its cambium surface. Probably no other problem in histologic physiology has been investigated so extensively and has given rise to more conflicting results. From a review of the literature, it is apparent that much of the conflict and confusion has arisen from