On the mediation by cell-cycle progression of cell-type differentiation. "I feel that embrologists do not ike to point out that their subject is contradictory to an idea favoured by molecular biologists. What I am proposing does not contradict any molecular biological principles, but it is something which would not be expected by molecular biologists.' On mesodermalization of amphibian ectoderm in realtion to experiments performed by Helmut Sauer.Handwritten.2-page letter