Albert BRACHET, founder of the Brussels School of embryology, conducted delicateexperiments in which he selectively destroyed zones of the grey crescentwith heated needles. This allowed him to observe, in 1923, that the medianregion of the grey crescent of the blastula is a area of spontaneous differentiationand that this «primary self-differentiation centre» organizesthe axial organs in anurans. It is thus fair to say that A. BRACHET contributed significantly to the emergenceof the organizer concept. Albert DALCQ and Jean PASTEELS, successors of A.BRACHET, trying to solve the problem of the organizer's determination, proposedtheir famous quantitative theory of embryonic development resulting in theconcept of morphogenetic potential, which increases with the CV concentration,a combination of a cortical constituent C and a vegetal substance V. Jean BRACHET, younger son of A. BRACHET and one of the founding father ofmolecular biology and embryology, was soon convinced that the organizer owesits inducing power to a chemical substance. Being the first to suggest therole of RNA in protein synthesis, he first imagined that RNA could be theactive substance in induction but became convinced afterwards that the inducedmust have a proteinic nature. His interest in the molecular aspects of inductionstimulated research that was to make chemical embryology molecular.