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: volume 27 includes letters from 1879, the year in which Darwin completed his manuscript on movement in plants. He also researched and published a biography of his grandfather Erasmus. The Darwins spent most of August on holiday in the Lake District. In October, Darwin's youngest son, Horace, became officially engaged to Ida Farrer, after some initial resistance from her father, who, although an admirer of Charles Darwin, thought Horace a poor prospect for his daughter.