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Darwin Correspondence Project

From Asa Gray   [early August 1856]1

–besides 20 or 30 of Introd. matter2 —(all simple & for students’ use)—among which is 4 pages of statistics.—of which I enclose you a proof of the last page, that you may see what our flora amounts to.3 The genera of the Crypt. Ferns—down to Hepaticæ—are illustrated in 14 crowded plates—so that the volume has become rather formidable as a Class-book—which is what it is intended for—

I have revised the last proofs to-day— The publishers will bring it out some time in August.— Meanwhile, I am going to have a little holiday, which I have earned, little as I can spare the time for it—and my wife and I start on Friday to visit my Mother and friends in W. New York, and on our way back I will look in upon the scientific meeting at Albany on the 20th inst. or later—just to meet some old friends there.4

Why could not you come over, on the urgent invitation given to European savans—& free passage provided back & forth in the steamers! Yet I believe nobody is coming. Will you not come next year, if a special invitation is sent you on the same terms?

Boott5 lately sent me your photograph,6 which (tho. not a very perfect one) I am well pleased to have.—

But there is another question in your last letter—one about which a person can only give an impression— And my impression is that—speaking of plants of a well-known flora—that what we call intermediate varieties are generally less numerous in individuals than the two states which they connect. That this would be the case in a Flora where things are put as they naturally should be, I do not much doubt, and the wider are your views about species (say for instance with Dr. Hooker’s very latitudinarian notions) the more plainly would this appear.—

But practically two things stand hugely in the way of any application of the fact or principle, if such it be, 1, Our choice of what to take as the typical forms very often is not free. We take, e.g. for one of them the particular form of which Linnæus, say, happened to have a specimen sent him, and on which established the species; and I know more than one case in which that is a rare form of a common species: the other var. will perhaps be the opposite extreme—whether the most common or not, or will be what L. or [Willd],7 say, described as a 2d species.— Here various intermediate forms may be the most abundant; 2d It is just the same thing now, in respect to specimens coming in from our new western country. The form which first comes & is described & named, determines the spec. char.— And this long sticks as the type, tho, in fact it may be far from the most common form.

Yet of plants very well known in all their aspects, I can think of several of which we recognize 2 leading forms, and rarely see anything really intermediate,—such as our Mentha borealis, its hairy and its smooth varieties.

Your former query, about the variability of Naturalized plants as compared with others of same genera, I had not forgotten, but have taken no steps to answer.— I was going hereafter to take up our list of naturalized plants & consider them, it did not fall into my plan to do it yet. Off hand I can only say that it does not strike me that our introduced plants generally are more variable, nor as variable, perhaps, as the indigenous. But this is a mere guess,—

When you get my sheets of 1st part of article in Sill. Journal,8 remember that I shall be most glad of free critical comments; and the earlier I get them, the greater use they will be to me.

Dr. Hooker writes me that he is to be off on the 12th inst to Switzerland, &c.— So I cannot write to him till his return.

One more favor: Do not I pray you speak of your letters troubling me. I should be sorry indeed to have you stop, or write more rarely, even tho’ mortified to find that I can so seldom give you the information you might reasonably expect from

Yours most | sincerely | Asa Gray

CD annotations

crossed pencil
scored brown crayon; ‘Q’added pencil
‘Q’added pencil
‘Q’added pencil
‘Q’added pencil
7.3 smooth varieties.] ‘(that may be jump)’ added pencil
double scored brown crayon
crossed pencil
Top of first page: ‘Intermediate forms. & [illeg]pencil; ‘5’ brown crayon, circled brown crayon; ‘B’ brown crayon, circled brown crayon; ‘20’9 brown crayon, circled brown crayon, del brown crayon
Bottom of last page: ‘Received Aug 20th. /1856/’


Dated on the assumption that the mail from Boston to England would have taken about two weeks (see CD’s annotations).
Gray refers to the proof-sheets of the forthcoming second edition of his Manual (A. Gray 1856a).
A. Gray 1856a, pp. xxv–xxviii, an ‘Arranged list of the natural orders of the flora of the northern United States, with the number of their genera and species, the number of introduced species, and of those common to Europe’.
The American Association for the Advancement of Science met in Albany, New York in 1856.
Francis Boott, a friend of CD, Gray, and Joseph Dalton Hooker, had settled in London and, after his retirement from medical practice, devoted his time to botany.
This may be the photograph taken by Maull and Fox (see Correspondence vol. 5, facing p. 448).
Karl Ludwig Willdenow.
The first part of Gray’s ‘Statistics of the flora of the northern United States’ (A. Gray 1856–7).
The ‘5’ may refer to chapter 5 of Origin; ‘20’ is the number of CD’s portfolio of notes on the geographical distribution of plants.


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 27 vols to date. Cambridge: Cambridge University Press. 1985–.

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.

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.


Believes intermediate varieties are generally less numerous in individuals than the two states that they connect.

Discusses the difficulties of deciding what is the typical form of a species

and gives some opinions on the variability of introduced species compared with indigenous species.

Letter details

Letter no.
Asa Gray
Charles Robert Darwin
Sent from
Source of text
DAR 165: 93
Physical description
4pp inc †

Please cite as

Darwin Correspondence Project, “Letter no. 1934,” accessed on 16 April 2021,

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