In the harvest of 1845 a disease, hitherto unknown in Ireland, phytophthora infestans, attacked the potato crop. The disease had made its appearance some years previously in north America and shortly afterwards in Europe. There is reason to believe that it already existed in south America, and it is possible that its failure to reach Europe with the early-introduced tubers was due to diseased tubers rotting during the long voyages under ‘ sail ’. The progress of the blight in European countries in the summer and early autumn of 1845 was reported in the Dublin Evening Post, which, without raising any serious alarm, pointed out the danger to the crop in Ireland. The seriousness of a failure of the staple food of the majority of the population must have been clear to every man struck by that possibility.