As the sheer volume of his correspondence indicates, 1862 was a very productive year for Darwin. This was not only the case in his published output (two botanical papers and a book on the pollination mechanisms of orchids), but more particularly in the extent and breadth of the botanical experiments he carried out. The promotion of his theory of natural selection also continued: Darwin's own work expanded on it, Thomas Henry Huxley gave lectures about it and Henry Walter Bates invoked it to explain mimicry in butterflies. This volume concentrates on the progress of his scientific work, but also records the effects of Darwin's continuing ill health and the serious illness of two of his children.