In 1879 he wrote and published a life of his grandfather, Erasmus Darwin, as “a preliminary notice” to the English translation of E. Krause’s Life; but Darwin’s contribution forms the larger part of the volume. CHAPTER XXIV. BOTANICAL WORKS (1862–86). Darwin’s botanical works are referred to separately, and receive more systematic treatment than the others, in the great “Life and Letters.” They form, together with the botanical letters, the subject of the seventh to the twelfth chapters in the last volume. It will therefore be unnecessary to treat them in any detail, although they form some of the most important and interesting of all his biological investigations. _Fertilisation of flowers._--“The Fertilisation of Orchids” was the first published of the botanical works, appearing in 1862, followed by a second and greatly altered edition in 1877. The object of the work “is to show that the contrivances by which orchids are fertilised are as varied and almost as perfect as any of the most beautiful adaptations in the animal kingdom; and secondly, to show that these contrivances have for their main object the fertilisation of the flowers with pollen brought by insects from a distant plant.” Even in 1837 Darwin had written in his note-book, “Do not plants which have male and female organs together [_i.e._ in the same flower] yet receive influence from other plants? Does not Lyell give some argument about varieties being difficult to keep [true] on account of pollen from other plants? Because this may be applied to show all plants do receive intermixture.” (Quoted in the “Life and Letters.”) In 1841, Robert Brown, the distinguished botanist, advised Darwin to read Sprengel’s “Secret of Nature Displayed” (Berlin, 1793). The result was to encourage and assist Darwin in his work on fertilisation of flowers by insects, and to bring about the first due recognition of Sprengel’s merits, long after his death. “_The Effects of Cross- and Self-fertilisation in the Vegetable Kingdom._”--This work has a very direct bearing on that last mentioned. Darwin speaks in the Autobiography “of having come [in 1839] to the conclusion in my speculations on the origin of species, that crossing played an important part in keeping specific forms constant.” Later on he came to see that the advantage of crossing is more direct, and results from the greater vigour of the offspring over those of self-fertilised plants. The object of this work, published in 1876, was to prove this point by experimental evidence of sufficient amount, and to show in numerous cases, by measurements of height or weight, or by counting the number of seeds produced, that cross-fertilisation invariably tends towards the greater vigour of offspring. Hence the motive cause for the marvellous adaptations by which cross-fertilisation is ensured was supplied. [Sidenote: FORMS OF FLOWERS.]