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Darwin Correspondence Project

From H. C. Watson   23 March 1858

Thames Ditton. S.W.

23 March/58

My dear Sir

As you write about not publishing for a couple of years, it is needless to send you the proof to which I alluded. It will be better sent in volume, when ready.1

I do not quite understand your query about the comparative range of species in large or small genera,—in its application to Cybele Britannica.2 The geographic area of almost every reliable species, found in the British Isles, is wider than those isles; the space over which it is spread in Britain being only a fragment or portion of its total area.

The Spiranthes cernua of South Ireland is the only exception, in addition to disputed species. Some of the most local of British plants have very wide geog-raphic areas, ex: gr: Cynodon Dactylon. Thus, whether widely or locally spread in Britain per se, is no test of the real area of a species.— Nor does frequency of repetition much avail; for some plants frequent in Britain, have rather restricted areas elsewhere, ex: gr: Erica cinerea.—

A much wider geographic area should be taken, than our Isles, to try whether the species of large genera, or of large orders, are more or less widely spread.—

I should quite expect that the species of small genera would be most widely spread, if this were tried by books;—because they are the species of large genera that Authors find most difficult to identify. If we believe our books, there are several species of Rubus, Rosa, Hieracium, Salix, &c. peculiar to Britain;—but these are likely enough species (true or false) not identified elsewhere, as the same, though existing elsewhere.—

One of my lists in the Volume printing will be a Census of species, with them all placed in sequence according to frequency of repetition & area; taking as thetest or measure the number of Provinces—Subprovinces—Counties & Vice-Counties.3 It has been an immense consumer of time, & is not quite done.

The number of provinces given in the 5 th. edition of the London Catalogue of British Plants is nearly correct & complete.4 Those numbers show the areas better than the smaller & more numerous subdivisions. The latter show the comparative frequency better.

I give these explanations, that you may judge whether I have aught in hand likely to meet your wants in details.—

But as I look upon the orders & genera of plants as purely conventional arrangements, not natural groups,—that is, not as groups in nature, but only as groups in books & herbaria;—the question whether the species of large or small orders are more common seems to me like a question of law,—one of human arrangement only.—

Very truly | Hewett C. Watson C. Darwin Esq

CD annotations

5.1 small genera] underl pencil
9.1 as purely] underl pencil
Top of first page: ‘LTR 18’5 pencil, del pencil; ‘50’pencil, underl pencil

Footnotes

CD had asked Watson about the publication date of the fourth volume of Watson 1847–59 (see letter from H. C. Watson, 3 January 1858).
CD had been calculating the geographical range of species, and seeing whether wide-ranging species were more common in large or small genera, using Watson and Syme 1857 (see Natural selection, pp. 138–40, 142–4). Watson’s Cybele Britannica (Watson 1847–59) specifically dealt with the geographical distribution of plants in Britain.
Watson’s most lasting contribution to the study of plant distribution was the terminology of provinces and counties, first explained in detail in Watson 1847–59.
Watson and Syme 1857. CD had based his calculations on the earlier edition of this work (Watson and Syme 1853). See Natural selection, p. 168.
CD numbered the letters he received from Watson.

Summary

Discusses the ranges of species in large and small genera; difficulties involved in limiting the discussion to Britain.

Letter details

Letter no.
DCP-LETT-2245
From
Hewett Cottrell Watson
To
Charles Robert Darwin
Sent from
Thames Ditton
Source of text
DAR 98: A23–4
Physical description
4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 2245,” accessed on 26 June 2019, http://www.darwinproject.ac.uk/DCP-LETT-2245

Also published in The Correspondence of Charles Darwin, vol. 7

letter