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Darwin Correspondence Project

To J. S. Henslow   7 July [1855]


July 7th

My dear Henslow

I write to thank you heartily for the seeds &c &c & all you have done.—

I do not think I have yet made it quite clear what I want marked in the Catalogue.1 (but I am really ashamed to be so troublesome) it is not so much what you “think may turn out varieties” (to quote your own words) but what you think are really species, but yet are very closely allied to some other species: I well know how vague this is, & perhaps you will find it impossible to do; but certainly, judging from what I have seen in animals, one pretty often meets a pair or more real (as far as one can judge) species, which yet are far more closely allied together than the average.

Of course there is always the possibility & even sometimes probability of these close species turning out varieties.—

Ever most truly yours | C. Darwin

Perhaps you might (if you can do the job) mark the closely allied species in connection, thus in an imaginary genus diag Quercus pedunculata X

rubra Quercus

alba Quercus

candida Quercus

sessiliflora X

alta Quercus

humilis X ramme

I shd. understand by this that you thought Q. pedunculata sessiliflora & humilis very closely allied species, but yet real species. I repeat perhaps the job will be impossible.—

P.S.2 | If you think fit you can entirely leave out such genera, as Rubus, Salix &c, in which I suppose hardly anyone knows what a species is. By species I mean the ordinary rather vague acceptation of the term. If you pass over any genus entirely, just score out the generic name.

I think you once wrote on vibrios in wheat;3 I found the other day an Agrostis with every germen, (at least I opened a full dozen), with 1 or 2, or 3 little worms in them, & no stamens or stigmas.—

I am working at all varieties & have now got 46 kinds of Peas all growing together!


See letters to J. S. Henslow, 27 June [1855] and 2 July [1855].
The postscript was written on a separate piece of paper. In Darwin and Henslow, it was transcribed at the end of a letter to Henslow, 23 [August–September 1855?] (see Darwin and Henslow, pp. 185–6), although the subject matter seems to indicate that it was associated with the present letter.
Henslow 1841.


Darwin and Henslow: Darwin and Henslow: the growth of an idea. Letters 1831–1860. Edited by Nora Barlow. London: John Murray. 1967.


Thanks JSH for seeds.

Clarifies his request about marking [London] catalogue [of British plants] – JSH is to mark those he thinks really are species, but which are very closely allied to some other species.

Letter details

Letter no.
Charles Robert Darwin
John Stevens Henslow
Sent from
Source of text
DAR 93: A36–A37, A114
Physical description
ALS 4pp

Please cite as

Darwin Correspondence Project, “Letter no. 1712,” accessed on 22 May 2022,

Also published in The Correspondence of Charles Darwin, vol. 5