My dear D^r. Gray

I have received the 2^d. part of your paper,² & though I have nothing particular to say, I must send you my thanks & hearty admiration. The whole paper strikes me as quite exhausting the subject, & I quite fancy & flatter myself I now appreciate the character of your Flora. What a difference in regard to Europe your remarks in relation to the genera makes! I have been eminently glad to see your conclusion in regard to species of large genera widely ranging: it is in strict conformity with the results I have worked out in several ways.³ It is of great importance to my notions.⁴ By the way you have paid me a great compliment; to be simply mentioned even in such a paper, I consider a very great honour.—⁵

One of your conclusions makes me groan, viz that the line of connection of the strictly Alpine plants is through Greenland: I sh^d. extremely like to see your reasons published in detail, for it “riles” me (this is a proper expression; is it not?) dreadfully.—⁶ Lyell told me, that Agassiz having a theory about when Saurians were first created, on hearing some careful observations opposed to this, said he did not believe it, “for Nature never lied”— I am just in this predicament & repeat to you that “Nature never lies”; ergo, theorisers are always right.—

In reading your paper, one point struck me as well worth working out, if it could be done, viz a comparison of the principal zone of habitation in the U. States of the 320 European plants in comparison with your 115 representative species + the 15 strongly marked varieties = 130 species; & there again rudely with the (4^th & 5) classes of Strictly Congeneric & perhaps divergent Congeneric species.—⁷ I should be astonished if you do not get a very curious & harmonious result, ie on the great principle that Nature never lies.—

Overworked as you are, I daresay you will say that I am an odious plague;—but here is another suggestion! I was led by one of my wild speculations to conclude (though it has nothing to do with geograph. distribution, yet it has with your Statistics) that Trees would have strong tendency to have flowers with dioicous, monoicous or polygamous structure. Seeing that this seemed so in Persoon, I took our little British Flora, & discriminating trees from Bushes according to Loudon, I have found that the result was in species, genera & Families, as I anticipated.⁸ So I sent my notions to Hooker to ask him to tabulate N. Zealand Flora for this end, & he thought my result sufficiently curious, to do so; & the accordance with Britain is very striking, & the more so, as he made 3 classes of Trees, Bushes, & herbaceous plants.—⁹ (He says further he shall work the Tasmanian Flora on same principle.) The Bushes hold intermediate position between the other two classes.— It seems to me a curious relation in itself, & is very much so, if my theory & explanation are correct.

With hearty thanks | Your’ most troublesome friend | Ch. Darwin

Pray do not forget variability of Naturalised plants.—¹⁰

P.S. | You might give me a valuable piece of information, with very little trouble to yourself.— I have been comparing, as far as I can, Protean genera, & have left off in a maze of perplexity. By Protean genera, I mean such as hardly two Botanists agree in about the species,—what to call species & what varieties. Now what I want to know is, whether such genera as Salix, Rubus, Rosa, Mentha, Saxifraga, Hieracium, Myosotis, &c have equally Protean species in U. States; even if they have only one, but more especially if they have many. I think you have no Rosa, & I forget how it is with some of the other genera.— The converse case w^d. be equally valuable to me if you would think over your half-dozen or dozen worst genera which have any European species, & then I could find out whether such are very troublesome in Europe.— I think Hooker told me that in Himalaya, Rubus & Salix, though large genera, were not troublesome to make out.— I think Protean genera of shells are troublesome at all geological times & in all places.