My Dear Lyell,

Very many thanks for sending me Hooker’s and Darwin’s letters, which I have read with great interest.¹ I agree in almost everything that Hooker says, as far as I can make him out, but his letter is very hard to read. I differ from Darwin as to the plants which he quotes, as instances of the occurrence of temperate forms on the Organ mountains; he seems to consider as a “temperate” genus every genus which is found at all in temperate climates, and here I think him mistaken.² I think I mentioned in my former letter, that, besides the strictly tropical forms on those peaks, there are species of genera which are very widely spread, and not specially either tropical or the reverse.³ Such a genus is Hypericum, one of those which Darwin enumerates; it is found in almost all parts of the world, except very cold countries. Clematis (which he does not mention) is another instance of the same kind. Drosera and Habernaria (as Hooker points out) have certainly their maximum within the tropics.⁴ If there are Vacciniums on the Organ mountains, they are of the sub-genus (Gaylussacia of Humboldt), which belongs specially to South America, and of which there is a species even on the coast of Brazil, in the island of St. Catherine.⁵

If the Brazilian mountains were once a branch of the Andes (which I infer is Darwin’s notion) I should have expected a greater number of the peculiar characteristic forms of the Upper Andes to be found on the mountains of Minus, &c., such as those “Rhododendrons of the Andes” (Befarius), of which Humboldt talks so much.⁶ There are some such: Gaultherias, Gaylussacias, Escallonias, &c., but not so many as one would expect. The strongest case, perhaps, in favour of Darwin’s view and against mine, is the genus Drimys (the Winter Bark). Whether the American forms of Drimys be all varieties of one species, or a group of closely allied species, they certainly afford a most striking instance of a group of very near relations ranging along the Andes, from Cape Horn all through South America into Mexico, and re-appearing conspicuously on the table land of Brazil.⁷ I do not know whether they are found anywhere between Minas and the Andes. It is certainly quite allowable for Darwin to say, that they must have migrated to the Brazilian uplands when these were more closely connected with the Andes than they now are. Fuchsia comes nearly into the same category with Drimys, except that there is a greater variety of forms, and some of them more decidedly distinct. I doubt whether either Fuchsia or Drimys is found very high up on the Andes.⁸

I acknowledge that, in my former letter, I did not sufficiently consider the possibility of the Organ mountains and those of Minas having been formerly much higher than now, and of their upper regions having been “glaciated” while in that position. But after all, as Hooker says, the information in Madame Agassiz’s letter is almost too vague to afford any safe ground for fighting upon. I think the meaning must be, that the “glacial” marks were observed down to (not up to) 3000 feet. This is a most material point.⁹

I do not agree with Darwin, that the nature of the vegetation of New Zealand, gives us reason to believe that tropical families of plants could bear a cold climate. However luxuriant the vegetation of New Zealand, it does not, I think, include any really tropical types.¹⁰ I am not sure, however, about Chiloe and Valdivia.¹¹

I am very glad to hear that Darwin’s health is better.¹²

Believe me ever your very affectionate Friend | Charles J. F. Bunbury

You may perhaps perceive that a certain degree of change has come over me while I have been writing this letter. I feel that I was perhaps too absolute in my first incredulity as to the possibility of glaciers on the Brazilian mountains: though I still think it quite incredible if they had only their present elevation; and I have recollected (as I noticed above) some instances of Brazilian plants which might with some plausibility be supposed to have migrated from the Andes.¹³