The Danish plant scientist Wilhelm Johannsen (1857-1927) is remembered for his experimental work on plant heredity, and as a founding figure of modern genetics. The terms 'gene', 'genotype' and 'phenotype' were first used by him. The results of his studies on beans supported theories advanced during the 1890s by the Dutch botanist Hugo de Vries, who had unknowingly replicated the work of Gregor Mendel, published in English translation in 1902 (also reissued in this series) by William Bateson. Johannsen's proposal that changes in heredity resulted from sudden mutations rather than from slow processes of natural selection was seen at the time as a threat to Darwinian theory, though later research showed otherwise. This influential book, first published in 1909 (with later editions in 1913 and 1926), is a revised, expanded German translation of a 1905 Danish book by Johannsen, itself based on a journal article originally published in 1903.