Chapter 336

Owing to all sorts of work, I have only just now finished reading your "Natural Conditions of Existence." (303/1. Semper's "Natural Conditions of Existence as they affect Animal Life" (International Science Series), 1881.) Although a book of small size, it contains an astonishing amount of matter, and I have been particularly struck with the originality with which you treat so many subjects, and at your scrupulous accuracy. In far the greater number of points I quite follow you in your conclusions, but I differ on some, and I suppose that no two men in the world would fully agree on so many different subjects. I have been interested on so many points, I can hardly say on which most. Perhaps as much on Geographical Distribution as on any other, especially in relation to M. Wagner. (No! no! about parasites interested me even more.) How strange that Wagner should have thought that I meant by struggle for existence, struggle for food. It is curious that he should not have thought of the endless adaptations for the dispersal of seeds and the fertilisation of flowers.

Again I was much interested about Branchipus and Artemia. (303/2. The reference is to Schmankewitsch's experiments, page 158: he kept Artemia salina in salt-water, gradually diluted with fresh-water until it became practically free from salt; the crustaceans gradually changed in the course of generations, until they acquired the characters of the genus Branchipus.) When I read imperfectly some years ago the original paper I could not avoid thinking that some special explanation would hereafter be found for so curious a case. I speculated whether a species very liable to repeated and great changes of conditions, might not acquire a fluctuating condition ready to be adapted to either conditions. With respect to Arctic animals being white (page 116 of your book) it might perhaps be worth your looking at what I say from Pallas' and my own observations in the "Descent of Man" (later editions) Chapter VIII., page 229, and Chapter XVIII., page 542.

I quite agree with what I gather to be your judgment, viz., that the direct action of the conditions of life on organisms, or the cause of their variability, is the most important of all subjects for the future. For some few years I have been thinking of commencing a set of experiments on plants, for they almost invariably vary when cultivated. I fancy that I see my way with the aid of continued self-fertilisation. But I am too old, and have not strength enough. Nevertheless the hope occasionally revives.

Finally let me thank you for the very kind manner in which you often refer to my works, and for the even still kinder manner in which you disagree with me.

With cordial thanks for the pleasure and instruction which I have derived from your book, etc.