THE third son of Charles Darwin gave early-evidence of a scientific bent. Born at Down a century ago, on August 16, 1848, he took his degree at Cambridge in 1870 with a first class in the Natural Sciences Tripos. After studying medicine at St. George‘s Hospital, London, and obtaining the Cambridge M.B. in 1875, he acted as his father‘s secretary for eight years. In 1884 he was appointed lecturer, and four years later reader, in botany at Cambridge. At that time plant physiology was beginning to supersede the study of systematic botanical description. Francis Darwin‘s class-book "The Practical Physiology of Plants" (1894) went into several editions, for it was the first book of its kind in Britain. His researches on growth curvatures in plants and on the control of water-loss by plants attracted considerable attention. He was a popular lecturer, being engagingly simple and direct. Though possessed of strong prejudices and inclined to be intolerant, his was a lovable personality, charming, kindly and humorous. He was an accomplished musician and devoted to dogs, which, unlike human beings, never bored him. Many honours came his way. Elected a fellow of the Royal Society in 1882, he was foreign secretary during 1903–9 and vice-president in 1907. In the following year he became president of the British Association, and he was knighted in 1913. He died at Cambridge on September 19, 1925. It is appropriate that his best and best-known book should be the "Life and Letters of Charles Darwin" (1887).