To J. D. Hooker   9 February [1858]1

Down Bromley Kent

Feb. 9th

My dear Hooker

I shd. be very much obliged for your opinion on enclosed.— You may remember in 3 first vols. tabulated, all orders went right except Labiatæ (By way if by any extraordinary chance you have not thrown away scrap of paper with former results I wish you would return it, for I have lost my copy, & I shall have all the division to do again; but do not hunt for it, for in any case I shd. have gone over calculation again.)2

Now I have done the 3 other vols.—3 You will see that all species in 6 vols together go right, & likewise all orders in the 4 last vols. except Verbenaceæ.4 Is not Verbenaceæ very closely allied to Labiatæ, if so one would think that it was not mere chance this coincidence? The species in Labiatæ & Verbenaceæ together are between $\frac{1}{5}$ & $\frac{1}{6}$ of all the species (15,645) which I have now tabulated.

Now bearing in mind the many local Floras which I have tabulated, (belting the whole northern hemisphere) & considering that they (& authors of D. C.Prodromus) would probably take different degrees of care in recording vari-eties; & the genera would be divided on different principles by different men &c, I am much surprised at uniformity of result, & I am satisfied that there must be truth in rule that the small genera vary less than the large.5 What do you think?

Hypothetically I can conjecture how the Labiatæ might fail, namely if some small divisions of the Order were now coming into importance in the world & varying much & making species: this makes me want to know whether you could divide Labiatæ into a few great natural divisions, & then I would tabulate them sep-arately as sub-orders;6 I see Lindley makes so many divisions, that there would not be enough in each for average.7 I send the Table of Labiatæ for the chance of your being able to do this for me: you might draw oblique lines including & separating both large & small genera.

I have, also, divided all the species into two equal masses; & my rule holds good for all the species in a mass in the 6 volumes; but it fails in several (4) large orders viz Labiatæ Scrophulareaceæ, Acanthaceaceæ & Proteaceæ.— But then when the species are divided into two almost exactly equal divisions; the division with large genera are so very few, for instance in Solanaceæ Solanum balances all others. In Labiatæ 7 gigantic genera balance all others (viz 113) & in Proteaceæ 5 genera balance all others. Now according to my hypothetical notions, I am far from supposing that all genera go on increasing for ever, & therefore I am not surprised at this result, when the division is so made that only a very few genera are on one side. But, according to my notions, the sections or sub-genera of the gigantic genera ought to obey my rule (ie supposing a gigantic genus had come to its maximum; whatever increase was still going on ought to be going on in the larger sub-genera.)

Do you think that the sections of the gigantic genera in D. C. Prodromus are generally natural; i.e. not founded on mere artificial characters. If you think that they are generally made as natural as they can be, then I shd. like very much to tabulate the sub-genera, considering them for the time as good genera. In this case, & if you do not think me unreasonable to ask it, I shd. be very glad of loan of Vols. X., XI, XII, & XIV. which include Acanthaceæ, Scrophulariaceæ, Labiatæ & Proteaceæ,—that is the orders, which when divided quite equally do not accord with my rule, & in which a very few genera balance all the others.—

I have written you a tremendous long prose. | Ever yours | C. Darwin.

Footnotes

Dated by the references to CD’s calculations using data from Candolle and Candolle 1824–73 (see nn. 2 and 3, below).
CD had calculated the number of species presenting varieties in large and small genera using volumes 2, 10, and 11 of Candolle and Candolle 1824–73 in December 1857 (see Correspondence vol. 6, letter from J. D. Hooker, [6 December 1857], and letter to J. D. Hooker, 9 December [1857]). His tables and calculations on this work are in DAR 15.2: 35–76.
Hooker had sent CD volumes 12, 13, and 14 of Candolle and Candolle 1824–73 (Correspondence vol. 6, letter from J. D. Hooker, [17–23 December 1857]).
CD’s results are given in a table in Natural selection, pp. 153–4.
For the floras that CD used to tabulate the number of varieties in large and small genera, see Correspondence vol. 6, letter to J. D. Hooker, 30 September [1857].
The order Labiatae was discussed by CD in Natural selection, pp. 155 & 156 n., because the result of his calculations on that group of plants opposed all the others. However, CD did not split the order into sub-orders as suggested here. He focused instead on the gigantic genera.

Bibliography

Candolle, Augustin Pyramus de and Candolle, Alphonse de. 1824–73. Prodromus systematis naturalis regni vegetabilis, sive enumeratio contracta ordinum generum specierumque plantarum huc usque cognitarum, juxta methodi naturalis normas digesta. 19 vols. Paris: Treuttel & Würtz [and others].

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

Lindley, John. 1846b. The vegetable kingdom. London: the author.

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.

Summary

Six volumes of Candolle’s Prodromus confirm rule that small genera vary less than large. Labiatae an exception to rule.

Letter details

Letter no.
DCP-LETT-2212
From
Charles Robert Darwin
To
Joseph Dalton Hooker
Sent from
Down
Source of text
DAR 114: 223
Physical description
8pp