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Darwin Correspondence Project

From Hewett Cottrell Watson   5 June 1856

Thames Ditton

June 5th 1856

My dear Sir

Allow me to suppose your letter divisible into four questions, instead of two.

1st. Sir Charles Lyell’s wish or advice seems sound, that you should not postpone publication of your views to a distant date;—rather, look forward to perfect or improve at the future time. 1

2d. My own volumes on distribution of British plants, prior to Cybele Britannica, were either three forms or three editions—expanding onwards.2 The third went very much into detail, but only one part (3 orders) was printed as an experiment, & not published. Had that third form been proceeded with, the information you want as to the species common to Europe & America would have been found. But as only 39 species were treated, the mere fragment would be practically useless. A Table or List in the second form (“Remarks”) attempts to give the information, but incompletely & too condensedly.3 At its date, the published data for America were far less ample & reliable than is now the case; & the distribution of the species beyond Britain was restricted to a single line for each. 4

3rd. America certainly possesses very few European species, which are absent from the Scandinavian Peninsula & Russia northward of 55o. Perhaps it cannot be said positively that no exceptions are found. But among the few which are reported to be so, some are highly questionable in respect to the identity of the species, or to the certain nativity on both continents. I will look out a few examples, to show what is here meant, & write them on a separate paper.5

4th. In England some 40 or 50 species of plants may be held as restricted, or almost restricted, to tillage ground (ploughed or dug); & about as many more are prevalent chiefly on such ground, altho’ more or less extending to road sides, sands, commons, old gravel pits, etc. I think these 50 or 100 species do not run into varieties more than other species of the same genera or same orders, which grow in other situations. If any difference in this respect, it may be that they are less widely variable, on an average, than are the non-agrarian species. But there are some striking instances of variability among the agrarians; and especially among those which grow also in other situations. For example, the varieties of Polygonum aviculare & Viola tricolor are numerous & wide; the agrarian forms differ much from those which grow in other situations; and the agrarian forms vary among themselves also. It would be easy to pick out three, or six, or perhaps more numerous varieties of either of these two species, which would have been received as so many good & distinct species, if they had been brought from different countries, & unaccompanied by those intermediate forms, which seemingly connect them into single species.6

Assuming that agrarian weeds differ less widely than others, on an average,—how far may this assumed fact be connected with another fact, that they are almost all of them Annuals? Ask of British botanists, which genera are their greatest opprobria in technical description,—in which is it most difficult to define & describe the Species, & to decide as to which forms should be called Species, & which should be called varieties?— They will answer, Salix, Rubus, Rosa, Mentha, Batrachium (sub-genus of Ranunculus), Potamogeton, Poa, Festuca, Viola, Galium,—Genera exclusively or chiefly of perennial Species.

You can make such use as you deem fit of answers to questions, which you pay me the compliment of asking;—but I fear the replies are unavoidably of that vague & unsatisfactory kind which must render them of no really available use—

Very faithfully | Hewett C. Watson To C. Darwin Esq

Examples of alleged American & European plants, not extending far north in Europe—7 Chrysosplenium oppositifolium. Said to occur in middle Russia & extending eastward to Altai. Absent from Sweden, but found in Denmark & the more southern portion of Norway. In Britain plentiful, extending to Orkney, & high on the Grampian Mountains. Absent from Shetland, Faroe, & more northerly isles. Was formerly held to be an American plant, found in various parts of Canada, &c. But in the Flo. Bor. Am. of Hooker the Eastern American plant is described as a distinct species, under name of Americanum.8 Still, Hooker keeps a Western form as a Variety of C. oppositifolium, viz. “β Scouleri”, from Columbia river; & he remarks on the resemblance of this Western-American form to the C. Nepalense of N. India, in its leaves, tho’ more like C. oppositifolium by its inflorescence. Thus, we have here a species which would have been deemed common to both Continents, tho’ not extended far northward in either, if the question had been asked some years ago. Now, they are either different “Species”, or different “varieties”. Looking beyond these two (“oppositifolium” & “β Scouleri”) we find Chamisso joining to them also the C. Nepalense & C. Kamtschaticum, as other varieties of the type species C. oppositifolium;9 thus tracing this last, but only in its alleged varieties, round the earth in latitudes which attain a culminating point northwards in Orkney. Isnardia palustris. Less of a boreal plant than the preceding. In Europe, attaining to the South of England, North of Germany, & S.E. of Russia. In America, to the Saskatchawan, & far southward.— Perhaps a true example,—but a semi-aquatic, widely distributed. Astragalus Hypoglottis. Absent from the Scandinavian Peninsula & N. Russia. Occurs in Scotland, Denmark, Island of Oesel, Middle Russia (say to lat 58o), Siberia. In British America, northward to the Saschatchawan river. Thlaspi alpestre.— England, Forfarshire, Gottland, Germany, &c; Absent from Russia, & Scandinavian peninsula. A single authority for its occurrence in Canada (Hooker Flo. Bor. Am.) but whether the author had seen specimens, or recorded on statement only, does not appear. Torrie & Gray simply copy, & add “Introduced?”10 But it is an unlikely plant to be introduced. The European “T. alpestre” has been latterly subdivided into various species by Jordan &c.11 Arenaria verna. Not admitted as a plant of Scandinavia, in the Summa Vegetabilium of Fries.12 It occurs on some few hills in Scotland, northward to Aberdeenshire. Hooker (Flo. Bor. Am.) says that the specimens from Canada & Western America correspond with the A. Verna of Britain. It is to be noted, however, that Ledebour (Flora Rossica)13 combines with this a number of so-called species, & thus makes the grouped forms, or the name, represent a species extending into arctic latitudes. Lythrum hyssopifolium— In Europe, northward to England & Lithuania; not in Denmark, Baltic Isles, or Scandinavian peninsula. Locally in the American States, & perhaps introduced. These half dozen species are perhaps as good examples as can be cited, of species alleged to be common to Europe & America, but having an early limit northward, comparatively with most species certainly common to both continents.

CD annotations

crossed pencil
crossed pencil
double scored pencil
Top of first page: ‘1’14 brown crayon; ‘Agrarian plants not variable some vars. confined to Fields.— Very few plants which do not range far n. are common to America’ pencil


CD ‘Began by Lyell’s advice writing species sketch’ on 14 May (‘Journal’; Appendix II). See also letter from Charles Lyell, 1–2 May 1856, n. 10.
Watson refers to the three editions of a work that he published under different titles: Outlines of the geographical distribution of British plants (Watson 1832); Remarks on the geographical distribution of British plants (Watson 1835); and The geographical distribution of British plants (Watson 1843). The third edition was, like the first, printed privately, and only one part was published, a copy of which is in the Darwin Library–CUL. The first volume of Cybele Britannica appeared in 1847 (Watson 1847–59). This work is also in the Darwin Library–CUL.
There are two tables in Watson 1835 pertinent to CD’s point. The ‘Table showing the number of British species found in other countries’ (Watson 1835, p. 113) indicates that some 480 species were common to North America and Britain. A much longer table (Watson 1835, pp. 187–258) attempted to show the ‘geographical extension of British plants beyond 30o N. latitude’ and was arranged species by species, as Watson mentions in the letter. CD recorded that he had read Watson 1835 on 15 June 1856 (Correspondence vol. 4, Appendix IV, 128: 18).
CD was writing a chapter on geographical distribution for his species book, the first draft of which was finished in July (Natural selection, p. 531). In this he cited the table to which Watson refers (see n. 3, above) but stated that ‘Mr. Watson informs me that since his publication in 1835 our knowledge has been much increased, & that the above numbers can be considered only as approximate.’ (Natural selection, p. 539). CD later deleted this discussion, adding in the margin: ‘No give Asa Gray’s facts, far more accurate’ (ibid., p. 539 n. 2). See letter to Asa Gray, 12 October [1856].
See the second part of the letter, following the valediction.
Watson’s comments on Polygonum aviculare are cited in Natural selection, p. 104.
CD used this information in Natural selection, p. 539.
W. J. Hooker 1840.
Chamisso 1831, pp. 557–8.
Torrey and Gray 1838[–43].
Jordan 1846[–9], pt 3: 1–34.
Fries 1846.
Ledebour 1842–53.
CD numbered Watson’s letters.


Answers CD’s questions about plants common to U. S. and Britain and their distribution in Europe.

Variability of agrarian weeds.

Letter details

Letter no.
Hewett Cottrell Watson
Charles Robert Darwin
Sent from
Thames Ditton
Source of text
DAR 181: 32
Physical description
11pp †

Please cite as

Darwin Correspondence Project, “Letter no. 1891,” accessed on 18 June 2019,

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