When I first came into personal relations with Darwin, after the death of Lyell in 1875, he was in the habit of deprecating any idea of his writing on theoretical questions. He used to talk of 'playing with plants and such things,' and undoubtedly derived the greatest pleasure from his ingenious experimental researches. The result of this 'play' in which Darwin took such delight is seen in his books on the _Power of Movement in Plants_ and _Insectivorous Plants_; full of the records of ingenious experiments and patient observation. It was a great relief to Darwin that his friend Wallace was able in 1871 to undertake the preparation of a work on _The Geographical Distribution of Animals_, for, on many points, the views held by Wallace on this subject were more in accordance with Darwin's own, than were those of Lyell and Hooker. Nevertheless, on all questions connected with the geographical distribution of plants, and the causes by which they were brought about, Darwin always expressed the fullest confidence in Hooker's judgment, and the greatest satisfaction with his results. With regard to another great division of his work, that dealing with the imperfection, but yet great value, of the geological record, Darwin was always anxious, when I met him, to learn of any new discoveries. But he felt that he had done all that was possible in his outline of the subject in the _Origin_, and that he must leave to palaeontologists all over the world the filling in of these outlines. So great was the delight with which he used to hear of new discoveries in palaeontology, that I often recall our conversations in these later days, when so many interesting forms of extinct animal and vegetable life--veritable 'missing links'--are being discovered in all parts of the globe, and wish that he could have known of them. They are indeed 'Facts for Darwin.' Very happy indeed was Charles Darwin in the last years of his useful life, in returning to his oldest 'love'--geology. In studying the action of earthworms he found a geological study in which his rare powers of ingenious experimentation could be employed with profit. His earliest published memoir had dealt with the question, and for more than forty years with dogged perseverance, he had laboured at it from time to time. It was delightful to watch his pleasure as he examined what was going on in the flower-pots full of mould in his study, and when his book was published and favourably received, he rejoiced in it as 'the child of his old age[144].'