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Darwin Correspondence Project

From Asa Gray   [August 1857]1

No one can have worked at systematic botany as long as I have, without having many misgivings about the definiteness of species.2 My notions about varieties are I believe just what you would have them See Sill. Jour. Sci. Jan. 1856. p. 136.:3 i.e. I believe every constitutional variety has a strong tendency to be perpetuated by seed, and the 2d. & 3d generations a stronger tendency still to transmit their inherited peculiarities. And when we see that every plant man takes in hand developes into varieties with readiness, when favorably circumstanced, we cannot avoid suspecting they may do the same thing—.i.e. sport in some way in the wild state also;—and that there is some law, some power inherent in plants generally prompting them to originate varieties.— —which is just what you want to come to, and I suppose this is your starting point.

Here you begin then with good, tangible facts; and I am greatly interested to see what is to be made out of them. First, can you get at the law of variation? or throw any ⁠⟨⁠section missing⁠⟩⁠

There is a good deal of fertilization in the bud, in various plants.4

I must look at Kidney beans in view of what you say.5

As to Fumariaceæ, I can’t imagine how, in Adlumia for instance, insects can get at the pollen very well, and still less how they can take any to the stigma of other blossoms.

But in most cases cross-fertilization seems a most likely thing to happen—

Kindly post the enclosed. I write in greatest haste, and am, with the highest regard

Ever Yours most faithfully | A. Gray

CD annotations

Top of first page: ‘Ch. 4’ink
Bottom of last page: ‘Ch. 3.’ink, circled ink;6 ‘Adlumia’ ink, circled ink


This letter falls between the letters to Asa Gray, 20 July [1857] and 5 September [1857].
Gray is responding to CD’s letter to Asa Gray, 20 July [1857], in which CD revealed his belief in the transmutation of species.
Gray added this reference to A. Gray 1856b in the margin of the letter in pencil.
See the earlier discussion of this point in the letter to Asa Gray, 18 June [1857], and the letter from Asa Gray, 7 July 1857.
The chapter numbers refer to chapter 3, ‘On the possibility of all organic beings occasionally crossing’, and chapter 4, ‘Variation under nature’, of CD’s species book (Natural selection, pp. 35–91, 95–171).


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.


States he has "misgivings about the definiteness of species". Believes there is some inherent tendency for plants to originate varieties. Cross-fertilisation is likely in most cases but sees difficulties with plants like Adlumia.

Letter details

Letter no.
Asa Gray
Charles Robert Darwin
Sent from
Source of text
DAR 165: 100, 101
Physical description
ALS 2pp inc †

Please cite as

Darwin Correspondence Project, “Letter no. 2129,” accessed on 2 March 2024,

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