Book excerpt: This volume is part of the definitive edition of letters written by and to Charles Darwin, the most celebrated naturalist of the nineteenth century. Notes and appendixes put these fascinating and wide-ranging letters in context, making the letters accessible to both scholars and general readers. Darwin depended on correspondence to collect data from all over the world, and to discuss his emerging ideas with scientific colleagues, many of whom he never met in person. The letters are published chronologically. In 1881, Darwin published his final book, The Formation of Vegetable Mould through the Action of Worms. He reflected on reactions to his previous book, The Power of Movement in Plants, and worked on two papers for the Linnean Society on the action of carbonate of ammonia on plants. In this year, Darwin's elder brother, Erasmus, died, and a second grandchild, also named Erasmus, was born.