The stabilization of cartilage properties in the cartilage‐forming mesenchyme of the embryonic chick limb

Experiments have been done to determine the time in the development of the embryonic chick limb when the cells in the cartilage‐forming area become “stabilized.” The particular criterion for stability used in this work was the ability of the cells to resist the influences in the limb which cause some limb mesenchyme cell to form cartilage and other limb mesenchyme cells to form soft tissue. Blocks of cartilage‐forming mesenchyme were transplanted from the cartilage‐forming area of a second limb to the prospective soft tissue area of a second limb. The host limb was permitted to develop for 48 hours, and then examined to determine if the implanted cells had formed cartilage outside of the normal cartilage pattern of the host limb. The embryos used as a source of the implanted blocks varied in stage from stage 22 to stage 27, the hosts also varied in stage from stage 22 to stage 27. It was found that a block of cartilage‐forming mesenchyme generally would conform with the host limb pattern if the donor was stage 24 or younger and the host was stage 24 or younger. A block of cartilage‐forming mesenchyme generally did not conform with the host limb pattern if the donor was stage 25 or older whatever the stage of the host. We conclude that the cartilage‐forming cells become stabilized by this criterion between stage 24 and stage 25.