AbstractA simple, rapid method is presented which permits qualitative evaluation of osteogenesis in tissue culture. Eleven‐day embryonic chick tibiae, with distal and proximal condyles removed, were grown in organ culture for two weeks. Explants demonstrated subperiosteal osteogenesis, bridging of fracture defects, and formation of bone,de novo, over the cut cartilaginous end surfaces of explants.The method presented herein has several advantages over those previously described and may be adopted for anin vitroassay of materials to determine direct effects on osteogenesis. Large quantities of explants can be prepared easily and cultured to yield consistantly abundant quantities of osteoid. Bone which is formed over ends of anlage is particularly significant by virtue of its position. New bone formed elsewhere in explants, with the possible exception of the fracture sites, however, is difficult to distinguish from bone present before onset of cultivation. Further more, osteogenesis which occurs over the cut cartilaginous ends after a week of culture, probably results from favorable environmental conditionsin vitroand not from cellular activity “preprogrammed”in ovo.In addition to osteogenesis, alteration of cartilage cells and matrix were observed in this system. Chondrocytes in the cut ends of the anlagen became spheroidal and resembled osteoblasts. Bone formation, however, was not observed about these cells. In and about lacunae of degenerating chondrocytes at the ends of the anlagen, collagen fibers app
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