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Darwin Correspondence Project

From H. C. Watson   19 November 1856

Thames Ditton

Nov. 19. 1856

My dear Sir

I had occasionally noticed common earth completely embedded within roots, & on one occasion had grounds almost beyond a doubt, to suppose that embedded seeds had germinated on exposure,— still, the idea of this, as a mode of navigation for seeds, never occurred to me until reading your letter,1 yet it is fairly within possibility, & perhaps even probability as a rare event.

In alluding to still water as hastening decay, I had in thought your remarks on the upper part of page 135,—not the germinating power of the seeds.2 It seems likely that plants would float longer, & thus be carried farther, on moving water, than might be inferred from their early decay & sinking in still water.—

As to the London Catalogue.—3 For the convenience of sorting duplicates, labelled accordingly, the Nos. prefixed to the specific names in the first edition have been kept on; the changes being usually interpolated by the Numeral repeated with an *.

I have run over the last, 4th., edition & get these results.— diag Species by Numerals 1428

Numbers interposed 0132



Numbers dropped out 0017


Actual Number 1543ramme

On reading over these 1543 specific names, I think about 200 of them represent ‘species’, which have either been treated expressly as varieties, or have not been distinguished from their nearest allied species, by Authors publishing more lately than the age of Linneus. Nearly 40 (36, it appears) of these belong to the one very unsettled genus Rubus.

You will recollect that all the names of varieties in the 4th. edition of the Catalogue, with Comparatively few exceptions (chiefly in Salix & Rubus), also represent ‘species’, so considered by some Authors.

In the lump, we may say of the Catalogue, that it includes over 1800 names of plants, which are (or recently have been) deemed species by one or more botanical writers of some authority. And that among these 1800 names of so supposed species, there are over 450 which represent what other botanical writers call varieties, not species.4

You will better see what I would convey by the alternative description, ‘treated expressly as varieties or not distinguished from near species’, if you will turn up the genus Ranunculus, in the first column of the Catalogue. Less than a century ago, all the species above Ficaria were held two only:— diag R. aquatilis.

R. hederaceus.ramme From the first of these, many years ago, were separated diag R. circinatus.

R. fluitans.ramme Opinions being much divided & long wavering, whether these two latter should be held species or varieties. The great majority, but not yet all botanical systematists, now admit them as species. Dr J. D. Hooker apparently holds them varieties.

A few years ago, two others were separated from R. hederaceus:— diag R. tripartitus.

R. cœnosus.ramme The former of these two is seemingly very local, & may not have ever been noticed apart from hederaceus (or even aquatilis, for it stands between) in England, until taken up as a species, & identified with a Continental one.— But R. cœnosus is widely & plentifully spread through England, & must have been often & constantly seen, & passed by as R. hederaceus, scarcely a variety, less than 20 years ago.

Still more lately, R. confusus has been cut off from R. aquatilis. And now, there are two or three others suggested, as similar “splits”.

You will see from this, that no clear separation can be made between “species” treated as varieties, & “species” not distinguished formerly.

I believe such instances as this may be found; the dates fanciful for the moment:— diag 1700 a. species

1111 b. species

1750 a. species

1111 b. variety

1800 ab species (sole)

1850 a. species

1111 b. variety

1856 a. species.

1111 b. species.ramme

The short truth is, that we have no real proof or test of a species in botany. We may indeed occasionally dis prove an alleged species by seeing its descendants become another such species,—or we may unite two by finding a full series of intermediate links. Many botanists assume all describable forms, if not (or until) so disproved or united, to be distinct species, ab initio ad finem.

I am making a sad scrawl, & just as the thoughts come of themselves, evidencing it to be a “rough draft”.—

Yours very truly | Hewett C. Watson C. Darwin | Esq

CD annotations

8.4 species] ‘7’ added pencil
Top of letter: ‘All used’pencil, circled pencil
Whole letter crossed pencil


CD’s letter has not been found. It was probably a reply to the letter from H. C. Watson, 10 November 1856.
Watson refers to CD’s paper ‘On the action of sea-water on the germination of seeds’ published in the Journal of the Proceedings of the Linnean Society (Botany) (see Collected papers 1: 268).
The London catalogue of British plants (Watson and Syme eds. 1853). CD had corresponded with Watson in 1855 about this work (see Correspondence vol. 5).
Watson’s figures from Watson and Syme eds. 1853 are cited in Natural selection, pp. 112–13.


Collected papers: The collected papers of Charles Darwin. Edited by Paul H. Barrett. 2 vols. Chicago and London: University of Chicago Press. 1977.

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

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.


Discusses means of seed transport.

Considers the difficulty of deciding which, if any, botanical species are real.

Letter details

Letter no.
Hewett Cottrell Watson
Charles Robert Darwin
Sent from
Thames Ditton
Source of text
DAR 98: A7–A10
Physical description
8pp †

Please cite as

Darwin Correspondence Project, “Letter no. 1994,” accessed on 3 August 2021,

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