skip to content

Darwin Correspondence Project

To Asa Gray   1 January [1857]1

Down Bromley Kent

Jan. 1st

My dear Dr. Gray

I have received the 2d. 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 shd. 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 (4th & 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 wd. 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.


Dated by the relationship to the letter from Asa Gray, 16 February 1857.
In his letter to Asa Gray, 2 May [1856], CD had asked Gray to examine the ranges of species in large and small genera of North American plants. CD expected large genera to include the most successful, and hence most common and most widely ranging, forms. CD had previously found some support for his views in A. de Candolle 1855, but Alphonse de Candolle’s evidence was not clear-cut because, CD believed, his comparison had been based on families rather than on genera. Gray had compared the species common to North America and Europe, first using families and then genera, and had concluded: ‘To be of any value, at least upon our limited scale, the comparison should be made with genera, as Mr. Darwin suggests’ (A. Gray 1856–7, p. 77).
See Natural selection, pp. 140–67, in which CD discussed ‘the relation of the commonness and diffusion of species to the size of the orders and genera in which they are included’. See also J. Browne 1980.
In mentioning CD’s views, Gray stated that ‘from some investigations of his own, this sagacious naturalist inclines to think that species in large genera range over a wider area than the species of small genera do.’ (A. Gray 1856–7, p. 77).
Comparing the northward range of species common to North America and Europe, Gray concluded that ‘it seems almost certain that the interchange of alpine species between us and Europe must have taken place in the direction of Newfoundland, Labrador and Greenland, rather than through the polar regions’ (A. Gray 1856–7, p. 73). CD, on the other hand, believed that a circumpolar flora had travelled only in a north–south direction to colonise lands in lower latitudes (Natural selection, pp. 539–42). See also letter from Asa Gray, 16 February 1857.
CD refers to the section entitled ‘Comparison of the flora of the northern United States with that of Europe in respect to the similar or related species’ (A. Gray 1856–7, pp. 78–84), in which Gray described five different categories of representative species: geographical varieties, very closerepresentative species, strictly representative species, strictly congeneric species, and divergent congeneric species.
Persoon 1805–7 and Loudon 1842 (see Natural selection, pp. 61–2). For Gray’s response to this query, see letter from Asa Gray, 1 June 1857.
CD had continued to remind Gray about this topic after having first mentioned it in his letter to Asa Gray, 2 May [1856]. See also letters to Asa Gray, 24 August [1856] and 24 November [1856], and letter from Asa Gray, 4 November 1856.


Browne, Janet. 1980. Darwin’s botanical arithmetic and the ‘principle of divergence’, 1854–1858. Journal of the History of Biology 13: 53–89.

Candolle, Alphonse de. 1855. Géographie botanique raisonnée ou exposition des faits principaux et des lois concernant la distribution géographique des plantes de l’époque actuelle. 2 vols. Paris: Victor Mason. Geneva: J. Kessmann.

Gray, Asa. 1856–7. Statistics of the flora of the northern United States. American Journal of Science and Arts 2d ser. 22: 204–32; 23: 62–84, 369–403.

Loudon, John Claudius. 1842. An encyclopaedia of trees and shrubs; being the arboretum et fruticetum Britannicum abridged. London.

Natural selection: Charles Darwin’s Natural selection: being the second part of his big species book written from 1856 to 1858. Edited by R. C. Stauffer. Cambridge: Cambridge University Press. 1975.

Persoon, Christiaan Henrik, ed. 1805–7. Synopsis Plantarum, seu enchiridium botanicum, complectens enumerationem systematicam specierum hucusque cognitarum. 2 pts. Paris and Tubingen.


Thanks AG for 2d part of "Statistics [of the flora of the northern U. S.", Am. J. Sci. 2d ser. 22 (1856): 204–32; 2d ser. 23 (1857): 62–84, 369–403].

Is glad AG concludes species of large genera are wide-ranging, but is "riled" that he thinks the line of connection of alpine plants is through Greenland. Mentions comparisons of ranges worth investigating.

Believes trees show a tendency toward separation of the sexes and wonders if U. S. species bear this out. Asks which genera are protean in U. S.

Letter details

Letter no.
Charles Robert Darwin
Asa Gray
Sent from
Source of text
Archives of the Gray Herbarium, Harvard University (7)
Physical description
ALS 10pp

Please cite as

Darwin Correspondence Project, “Letter no. 2034,” accessed on 25 July 2024,

Also published in The Correspondence of Charles Darwin, vol. 6