Thanks CD for noticing some difficulties in his hypothesis. Concedes that there is no proof that higher plants are more intolerant of carbon dioxide than lower plants. Argues that the main difference between the lowlands and the high mountains in Palaeozoic times would be the much greater climatic fluctuations that would occur on the mountains. Discusses carbon dioxide diffusion in the Palaeozoic atmosphere. Thinks that the large number of species and genera peculiar to high mountains favours the assumption that "their diffusion must date from a geologically remote period" [see ML 2: 20–2].