Rosalind Franklin's first important contributions to the model popularised by Crick and Watson was her lecture at the seminar in November 1951, where she presented to those present, among them Watson, the two forms of the molecule, type A and type B, her position being that the phosphate units are located in the external part of the molecule. She also specified the amount of water to be found in the molecule in accordance with other parts of it, data that have considerable importance in terms of the stability of the molecule. Franklin was the first to discover and formulate these facts, which in fact constituted the basis for all later attempts to build a model of the molecule. However, Watson, at the time ignorant of the chemistry, failed to comprehend the crucial information, and this led to the construction of a wrong model.