The Substratum for Bone Morphogenesis11This work was aided by a grant-in-aid from The John A. Hartford Foundation, Inc., and in part by grants-in-aid from the USPHS, National Institute of Dental Research (DE-02103), Ayerst Laboratories, Inc., and the Orthopedic Research and Education Foundation; and in part by a contract between the U. S. Army Research and Development Command (DA-49-193 MD-2556) and the University of California.