To Asa Gray   9 May [1857]¹

My dear D^r. Gray

I must thank you for your new part of Statistics:² if feeling the most lively interest in reading it can make me worthy of receiving it, assuredly I am worthy. I will not trouble you by specifying the many points which have particularly struck me; but the note at p. 387 I must allude to, as I want to ask a question which I think it cannot take 5 minutes to answer, namely to how many genera the 49 species belong: as there are six species of Carex there cannot be more than 44: I tried to go through list, but I c^d. not feel sure in separating the 3^d head from 1^st & 2^d. Heads.—³ I want to know to see more clearly in proportion to your whole Flora how large the proportion of monotypic genera is in the disjoined species. This subject interests me very much: I began to try to work out this point in all the cases of much disjoined species which I met with; but I failed from want of knowledge: I tried also to make out whether the disjoined species would not on average belong to small Families, but here again I failed from want of knowledge; though the cases in which I could find out something, confirmed my very strong expectation that species having disjoined ranges would belong to small genera;⁴ so you may imagine how much interest I felt in coming on your note on this very subject.—

Your list of the Trees made my mouth rather water to know what proportion had sexes in some degree separated,—on which subject I wrote you a ridiculously long letter some weeks ago.⁵

I am so glad that you are going to attack your introduced plants in the next number:⁶ I may mention that two or three years ago I compared the proportions of the British introduced species, to the native Flora & it was in several cases ridiculously close: I then took your first Edition⁷ & did the same, but the proportions here were very different; but I think this point w^d. be just worth looking to, for chance of some result.

I have just looked at my old useless notes, & I see I made out in your Manual 206 introduced plants & of these Compositæ form 18 & so do (as I thought) your indigenous compositæ.—⁸

In Britain from H. Watson’s Cybele⁹ diag Introduced——Indigenous

Compositæ $\frac{1}{10}$ $\frac{1}{9}$

Umbelliferæ $\frac{1}{22}$ $\frac{1}{23}$

Labiatæ $\frac{1}{28}$ $\frac{1}{30}$

Leguminosæ $\frac{1}{20}$ $\frac{1}{18}$ ramme

I happened to stumble on these results first, & was inclined to think something of them; but I suppose all was chance or errors. The standard proportion ought to be, I sh^d think, that for world in same latitude, & not the standard of the individual country. Though why I sh^d. trouble you with an old exploded notion of mine, I know not.

With my sincere thanks & good wishes.—

Believe me | Your’s most sincerely | Ch. Darwin