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Darwin Correspondence Project

To Asa Gray   9 May [1857]1

Down Bromley Kent

May 9th

My dear Dr. Gray

I must thank you for your new part of Statistics:2 if feeling the most lively interest in reading it can make me worthy of receiving it, assuredly I am worthy. I will not trouble you by specifying the many points which have particularly struck me; but the note at p. 387 I must allude to, as I want to ask a question which I think it cannot take 5 minutes to answer, namely to how many genera the 49 species belong: as there are six species of Carex there cannot be more than 44: I tried to go through list, but I cd. not feel sure in separating the 3d head from 1st & 2d. Heads.—3 I want to know to see more clearly in proportion to your whole Flora how large the proportion of monotypic genera is in the disjoined species. This subject interests me very much: I began to try to work out this point in all the cases of much disjoined species which I met with; but I failed from want of knowledge: I tried also to make out whether the disjoined species would not on average belong to small Families, but here again I failed from want of knowledge; though the cases in which I could find out something, confirmed my very strong expectation that species having disjoined ranges would belong to small genera;4 so you may imagine how much interest I felt in coming on your note on this very subject.—

Your list of the Trees made my mouth rather water to know what proportion had sexes in some degree separated,—on which subject I wrote you a ridiculously long letter some weeks ago.5

I am so glad that you are going to attack your introduced plants in the next number:6 I may mention that two or three years ago I compared the proportions of the British introduced species, to the native Flora & it was in several cases ridiculously close: I then took your first Edition7 & did the same, but the proportions here were very different; but I think this point wd. be just worth looking to, for chance of some result.

I have just looked at my old useless notes, & I see I made out in your Manual 206 introduced plants & of these Compositæ form 18 & so do (as I thought) your indigenous compositæ.—8

In Britain from H. Watson’s Cybele9 diag Introduced——Indigenous

Compositæ 110 19

Umbelliferæ 122 123

Labiatæ 128 130

Leguminosæ 120 118 ramme

I happened to stumble on these results first, & was inclined to think something of them; but I suppose all was chance or errors. The standard proportion ought to be, I shd think, that for world in same latitude, & not the standard of the individual country. Though why I shd. trouble you with an old exploded notion of mine, I know not.

With my sincere thanks & good wishes.—

Believe me | Your’s most sincerely | Ch. Darwin


The year is given by CD’s acknowledgment of the receipt of the third part of A. Gray 1856–7 (see n. 2, below).
The third and final part of A. Gray 1856–7 was published in the May 1857 issue of the American Journal of Science and Arts. CD’s copy is in DAR 135 (3).
Discussing species ‘of widely sundered habitation’, or the so-called ‘disjoined’ species of Alphonse de Candolle, Gray enumerated those species that ‘re-appear in Japan, the Himalaya, or some part of North Asia, but are not European’ (A. Gray 1856–7, p. 387). Dividing this group into two subclasses, the first being those common to north-west America and Japan and the second being those common to the Himalayas, Europe, and North America, Gray added the following note (A. Gray 1856–7, p. 387 n.), to which CD refers: Out of 49 species belonging to these first and second heads, as many as 10 belong to monotypic genera, and 21 to genera of less than ten good species;—six of the species belong to the vast genus Carex;—on the whole rather militating against the idea that the geographical extension of species bears some proportion to the size of the genus they belong to. Part of CD’s confusion is a result of an error Gray made in his note (see letter from Asa Gray, 1 June 1857).
CD explained why he expected species with disjoined ranges to be found in small genera in letter to Asa Gray, 18 June [1857].
In the event, Gray was not able to prepare this paper. See letter from Asa Gray, 1 June 1857.
These notes are in DAR 46.2 (ser. 2): 38–41. CD discussed the naturalised plants of North America in Natural selection, p. 232 and n. 3, and in Origin, p. 115, but having retabulated his results using the second edition of Gray’s Manual (A. Gray 1856a).
Watson 1847–59. The calculations are in DAR 46.2 (ser. 2): 42–58. See Correspondence vol. 5, letter to J. D. Hooker, 13 April [1855], for CD’s earlier comments on these statistics.


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.

Gray, Asa. 1848. A manual of the botany of the northern United States, from New England to Wisconsin and south to Ohio and Pennsylvania inclusive. Boston and Cambridge: James Monroe and Company. London: John Chapman.

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.

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.

Origin: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. By Charles Darwin. London: John Murray. 1859.

Watson, Hewett Cottrell. 1847–59. Cybele Britannica; or British plants and their geographical relations. 4 vols. London: Longman.


Thanks for new part of "Statistics".

Interested in disjoined species; do they tend to belong to large or small genera, and are they generally members of small families?

Is glad AG will tackle introduced plants; has noticed that the proportion of a particular family to the whole flora tends to be similar in introduced and indigenous plants.

Letter details

Letter no.
Charles Robert Darwin
Asa Gray
Sent from
Source of text
Archives of the Gray Herbarium, Harvard University (9)
Physical description
ALS 8pp

Please cite as

Darwin Correspondence Project, “Letter no. 2089,” accessed on 30 January 2023,

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