[In the letters already given we have had occasion to notice the general bearing of a number of botanical problems on the wider question of Evolution. The detailed work in botany which my father accomplished by the guidance of the light cast on the study of natural history by his own work on Evolution remains to be noticed. In a letter to Mr. Murray, September 74th, 1861, speaking of his book on the ‘Fertilisation of Orchids’ he says: “It will perhaps serve to illustrate how Natural History may be worked under the belief of the modification of species.” This remark gives a suggestion as to the value and interest of his botanical work, and it might be expressed in far more emphatic language without danger of exaggeration.

In the same letter to Mr. Murray, he says: “I think this little volume will do good to the ‘Origin,’ as it will show that I have worked hard at details.” It is true that his botanical work added a mass of corroborative detail to the case for Evolution, but the chief support to his doctrines given by these researches was of another kind. They supplied an argument against those critics who have so freely dogmatised as to the uselessness of particular structures, and as to the consequent impossibility of their having been developed by means of natural selection. His observations on Orchids enabled him to say: “I can show the meaning of some of the apparently meaningless ridges, horns; who will now venture to say that this or that structure is useless?”