Comprising: "Some Problems of the Cell Nucleus", a lecture given at Yale University, 5 September 1950, including a letter from Joseph Chayen enclosing 3 black-and-white photographs of Tradescantia bracteata staminal hair nuclei, 30 August 1950, and 6 black-and-white photographs used as slides and described in accompanying notes; and "An Experiment in Biophysics", a lecture given at the Royal Society, 1 February 1951, with 2 black-and-white photographs and various diagrams and photographs from offprints, perhaps used as slides.