My dear Darwin

I feel that I should have answered your letter some time ago, if it were only to thank you for the most kind, but far too flattering sentiments towards me which it contains. My last to you must have been, I feel sure, a most grumbling & ill tempered communication, for it was composed under the irritation produced by news which did not please me, though if I am to believe me friends, who do surely know better than myself, I ought to be very thankful that such a situation as Edinbro’ affords is open, if only to be tried for. My Father is so anxious for me to be home soon, that he desired me not to go to Germany, but allowed of my return by Belgium & Holland, though he did not grant me so much time as I have staid; but then I have taken the liberty to allow of a little paternal over-anxiety, & have also a strong wish to see all in these countries, that Germany may be taken by itself another time, should I ever be so fortunate as to compass a second continental tour. Your messages to Ehrenberg & to Dieffenbach I sent in my own name to my good friend Klotsczh, of the Herb. Reg. Berol.,¹ & they will I am sure be duly attended to.

Most heartily did I wish for your company over & over again in Paris, for Humboldt had lots of time there, & such quantities of things to ask about, that demanded much better answers than I could give: the more I saw of him, & he either came to my room or sent for me almost every morning, the more I liked him, to be sure his amazing volubility & the constant practice of quoting himself, his travels & his works, for every subject, savours somewhat of old age, but those who know him best, say that he must not be so judged, as he was ever the same in his younger days. Further, his habit of always asking questions & seldom proposing a subject for mutual discussion, or giving his own information except when asked, leads one to suppose, that he is collecting more materials than he has time to arrange or dispose of: but as I saw more of him, it became more & more evident, that his mind was still vigorous, that he was still a most extraordinary man.

Nothing proved this more than my proposing the question, (which I am truly ashamed to have forgotten till you so kindly reminded me of it), concerning the N.E. Europe river dividing two Bot. regions. I do not suppose that he drew breath for 20 minutes, during which he was engaged in telling all he knew on the distrib. of Siberian plants &c. The river is the Obi, to the E. of the Oural, to its W. bank Rhododendrons some Coniferæ & other marked plants proceed, & occupy the plains on both sides of the Irtych, but though these inhabit the W. bank itself of the Obi they do not cross it: some other facts connected with this river & subject, are to be found in Gmelin’s Botany of Siberia,² a work we have, but which I have almost neglected. Another most singular fact in the Botany of these regions Humboldt also told me of, & that was, that all the rivers to the W. of the Oural are covered (their banks) with Oaks: none of them to East are, nor are these trees met with in any part of Siberia, until reaching the waters of the Arnour & other Chinese rivers, given off from the Yablonoi & Stanavoi ranges, what is still more remarkable is, that the said rivers both of W. Oural & Arnour have fresh-water lobsters, equally foreign to all the Siberian waters. The absence of Lobsters & Oaks in all the countries watered by the Siberian rivers is a wonderful fact & to Humb. quite inexplicable. The only analogous facts I know off are those connected with the difference of the Floras of Greenland & W. Baffins bay, which are in every respect trifling in comparison. Such are Humboldts strong arguments against the migration of species, a doctrine he has most studiously & repeatedly warned me against, as wholly untenable, ever quoting the to him unaccountable fact, that the Befarias of the Caraccas & Andes should be the same, without a double creation; ³ (there is no smothering the truth that he is garrulous upon his own observations).

Fancy my amazement, on being shewn by him one day, 15 sheets of Kosmos, all printed, all just arrived from Germany & all to be corrected together!—⁴ In common with many other Paris men, I had given Kosmos up, especially as he himself had told me that it would not be finished for two years—the two first parts are to appear this year, no 1 is ready, 3 will conclude it. As an instance of the man’s extraordinary memory, I may tell you that he gave me the heads of all the subjects of the two first parts, without once stopping, I do think he was almost $\frac{1}{4}$ hour incessantly going on, from one head to another: the general nature of the work is, a review of the present state of our knowledge of Astronomy physics & natural History

The Paris Botanists have little or nothing to say about Geographical distribution, they are far more occupied with Anatomical & Physiological questions. One thing they all appear to agree in is, that we want facts to generalize upon & all incline to the migrating side, as however they do so without examining for themselves, their opinion does not carry much weight. You know what my own sentiments were, that I considered migration to a great extent, as, at any rate a precipitate conclusion, & this after having paid some little attention to the subject. I now, chiefly from the results of working out your suggestions, incline to consider migration as the only cause of the dispersion or diffusion of a so called species. Nothing that Humboldt has said hitherto alters my opinion, though I can no more account for Rhododendrons not crossing the Obi, than for Eryngium campestris & many other Continental weeds not crossing the channel, though they run wild when brought across. Nothing will be more likely to settle my own mind satisfactorily, than a comparison of my Southern plants with those of the N. Hemisp. of those there are a proportion common to both temperate regions, should I be able to trace the majority of them from one zone to the other, I shall declare myself a good migrationist, if not I must hold the question still unsettled; in this work I am at present interrupted.

The change of Wheat into Rye is here wholly disbelieved; Lindley, who you would suppose from his English writings, puts some faith in it,⁵ strongly denies all belief in it to Decaisne:⁶ the latter told me that a person had produced accidentally, by sowing wild Strawberry seeds one plant with simple, not ternate, leaves, & that it again reproduced simple-leaved plants, this is something like Dorking fowl.⁷ Some make use of such exceptions to deny the existence of species at all, I have a tract on the subject for your perusal.⁸ Perottet declares the vegetation of the tops of the Nylgherries to be quite European.⁹ Have you seen Hind’s paper on Sandwich Isld Botany?¹⁰ from what I read of it he seems wholly, entirely ignorant of the subject, I saw it hurriedly at Delesserts¹¹ & it appeared that he takes no notice of the most striking facts.

Decaisne is certainly the most promising Botanist of the day, he has lately established as good sexes in Algæ as are to be found in other cryptogamic plants,¹² which however is nothing to a new light¹³

I will send you D’Urville when I return, I have got letterpress only.¹⁴ You could not have pleased Humboldt better than by your message, he was delighted, he certainly is failing fast, he never talks of his Asia voyage, all is of S. America.