My dear Hooker

I had intended writing to you today, had I not received yesterday’s enclosure to remind me. Many thanks for the seed & for sending me your curious account of the antarctic ice, which no doubt, together with your notes on Infusoria, Ehrenberg w^d be very glad to see.— I sent my last parcel through M^r Taylor of Fleet St. or rather, (I believe) through M^r Francis, who lives with him.— The homogeneous manner in which the brash¹ is coloured, certainly appears very curious; I presume you consider the quantity too great for snow; with respect to its rising from the bottom, I sh^d rather doubt it, though in fresh running water, it is well known that icy matter, I suspect like your brash, rises from the bottom, & brings with it stones. There has been much argument about cause of this, in which even Arago has joined:² the best explanation offered, as it appeared to me, was that the bottom of the stream lost its heat by radiation & and the water froze on it. Should you feel much interest on this subject, I could look you up, (I think) some references. One w^d doubt, whether the bottom of the sea would lose its heat by radiation through several hundred feet of thickness of water, & the whole body of water would have to be cooled to the freezing point of sea-water. On other hand Simpson & Deane (I think) found the bottom of shallow arctic sea hard frozen:³ off Spitzbergen masses of ice suddenly rise from the bottom, I have fancied they were remnants of fixed & grounded icebergs.

What a curious, wonderful case is that of the Lycopodiums; I suppose you would hardly have expected them to be more varying than a phanerogamic plant. I trust you will work the case out & even if unsupported publish it, for you can surely do this with due caution. I have heard of some analogous facts, though on the smallest scale, in certain insects being more variable in one district than in another; & I think the same holds with some land-shells. By a strange chance, I had noted to ask you in this letter an analogous question, with respect to genera, in lieu of individual species⁴ —that is, whether you know of any case of a genus with most of its species being variable (say Rubus) in one continent, having another set of species in another continent non-variable or not in so marked a manner.⁵ M^r Herbert incidentally mentioned in a letter to me, that the Heaths at the C. of Good Hope were very variable, whilst in Europe they are (?) not so (?); but then the species here are few in comparison, so that the case, even if true, is not a good one.—⁶ In some genera of insects the variability appears to be common in distant parts of the world: in shells, I hope hereafter, to get much light on this question through fossils. If you can help me, I sh^d be very much obliged: indeed all your letters are most useful to me.

Monday— Now for your first long letter & to me quite as interesting as long. Several things are quite new to me in it, viz for one, your belief that there are more extra-tropical than intratropical species. I see that my argument from the Arctic regions is false, & I sh^d not have tryed to argue against you, had I not fancied that you thought that equability of climate was the direct cause of the creation of a greater or lesser number of species: I see you call our climate equable, I sh^d have thought it was the contrary; anyhow the term is vague, & in England will depend upon whether a person compares it with the United States or T. del Fuego.— In my Journal, (p. 342) I see I state that in South Chiloe at height of about 1000 ft the forest had a Fuegian aspect: I distinctly recollect, that at sea-level in middle of Chiloe, the forest had almost a tropical aspect. I sh^d. like much to hear, if you make out, whether the N. or S. boundaries of a plant are the most restricted; I sh^d have expected that the S. would be, in the temperate regions, from the number of antagonist species being greater. (N.B. Humboldt, when in London, told me of some river in N. E. Europe, on the opposite banks of which the Flora was, on the same soil & under same climate, widely different!)⁷ I forget my last letter, but it must have been a very silly one, as it seems I gave my notion of the number of species being in great degree governed by the degree to which the area had been often isolated & divided;; I must have been cracked to have written it, for I have no evidence, without a person be willing to admit all my views, & then it does follow; but in my most sanguine moments, all I expect, is that I shall be able to show even to sound Naturalists, that there are two sides to the question of the immutability of species;—that facts can be viewed & grouped under the notion of allied species having descended from common stocks. With respect to Books on this subject, I do not know of any systematical ones, except Lamarck’s, which is veritable rubbish; but there are plenty, as Lyell,⁸ Pritchard⁹ &c, on the view of the immutability. Agassiz lately has brought the strongest arguments in favour of immutability.¹⁰ Isidore G. St. Hilaire has written some good Essays, tending towards the mutability-side, in the “Suites à Buffon”, entitled “Zoolog: Generale”.¹¹ Is it not strange that the author of such a book, as the “Animaux sans Vertebres”,¹² sh^d have written that insects, which never see their eggs, should will, (& plants, their seeds) to be of particular forms so as to become attached to particular objects.¹³ The other, common (specially Germanic) notion is hardly less absurd, viz that climate, food, &c sh^d make a Pediculus formed to climb Hair, or woodpecker, to climb trees.— I believe all these absurd views, arise, from no one having, as far as I know, approached the subject on the side of variation under domestication, & having studied all that is known about domestication.— I was very glad to have your criticisms on island-floras & on non-diffusion of plants: this subject is too long for a letter; I c^d. defend myself to some considerable extent, but I doubt whether successfully in your eyes, or indeed in my own.

I sh^d be much obliged for a loan of the Tasmanian Journal with Rev^d: Clarke’s Paper: I suspect, however, it will turn out to be the same with a paper read by him before the Geolog: Soc: on the same subject.—¹⁴ I shall be in town on the 20^th.: could you leave it for me at the Athenæum (Have you your name down for this club? I think you w^d find it worth while, if you have not) or at the Geolog: Soc:—

Is there any chance of your being able to pay us a visit here soon; it would give M^rs. Darwin & myself real pleasure. I sh^d have written sooner, had not my own plans, owing to a visit to my Fathers now paid, been rendered uncertain. We c^d send to meet you to Croydon; or you c^d come by Coach from the Bolt-in-tun Fleet St.— We are wholly disengaged, except on 19, 20, 21, when I must be in London on business.

Once again, thanks for your Botanical letters & believe me, my dear Hooker, | Very truly yours | C. Darwin

Will you tell Sir William, that the Deodar, which he gave me, is doing famously.

I am really ashamed how infamously this letter is written.—