My dear Hooker

I sh^d. 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 sh^d. 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 sh^d. 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 sh^d. 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.