To Asa Gray 12 October 1
Down Bromley Kent
My dear Dr. Gray
I received yesterday your most kind letter of the 23d. 2 & your “Statistics” & two days previously another copy.3 I thank you cordially for them. Botanists write, of course, for Botanists; but as far as the opinion of an “outsider” goes, I think your paper admirable. I have read carefully a good many papers & works on Geograph. Distribution, & I know of only one Essay (viz Hooker’s N. Zealand)4 that makes any approach to the clearness with which your paper makes a non-Botanist appreciate the character of the Flora of a country. It is wonderfully condensed (what labour it must have required!): you ask whether such details are worth giving, in my opinion there is literally not one word too much.
I thank you sincerely for the information about “social” & “varying plants”; & likewise for giving me some idea about the proportion (ie ) of European plants, which you think do not range to the extreme north: this proportion is very much greater than I had anticipated from what I picked up in conversation &c.—5
To return to your Statistics: I daresay you will give how many genera (& orders) your 260 introduced plants belong to: I see they include 113 genera non indigenous: as you have probably a list of the introduced plants, would it be asking too great a favour to send me per Hooker or otherwise just the total number of genera & orders to which the introduced plants belong:6 I am much interested on this, & have found De Candolles remarks on this subject very instructive.7
Nothing has surprised me more than the greater generic & specific affinity with E. Asia than with W. America. Can you tell me (& I will promise to inflict no other question) whether climate explains this greater affinity? or it is one of the many utterly inexplicable problems in Bot. Geography? Is E. Asia nearly as well known as West America? so that does the state of knowledge allow a pretty fair comparison?8
I presume it would be impossible, but I think it would make in one point your tables of generic ranges more clear (admirably clear as they seem to me) if you could show, even roughly, what proportion of the genera in Common to Europe (ie nearly half) are very general or mundance rangers; as your results now stand at the first glance the affinity seems so very strong to Europe, owing, as I presume to the (nearly) half of the genera including very many genera common to the world or large portions of it. Europe is thus unfairly exalted.— Is this not so? If we had the number of genera strictly or nearly strictly European, one could compare better with Asia & southern America &c. But I daresay this is a Utopian wish owing to difficulty of saying what genera to call mundane. Nor have I my ideas at all clear on subject, & I have expressed them even less clearly than I have them.
I am so very glad that you intend to work out N. range of the 321 Europæan species; for it seems to me the by far most important element in their distribution.—
And I am equally glad that you intend to work out range of species in regard to size of genera ie number of species in genus.— I have been attempting to do this in a very few cases; but it is folly for any one but Botanist to attempt it: I must think that De Candolle has fallen into error in attempting to do this for Orders instead of for genera,—for reasons with which I will not trouble you.—9
In second column Heading p. 27 (or p. 229) there is misprint “and,” for “not”, which might seriously mislead an idle reader who only looked at general totals.
Many of our Societies always page their separate copies of papers with the proper pages for reference. Is not this good scheme & worth Prof. Silliman attending to? by a reference in body of your own paper I have corrected your paging.10
Hooker has lately returned from his continental trip & I am going to see him on Friday. Have you seen his Review on Decandolle: I cannot but think he is rather too severe on want of originality, & I hope much too severe on whole great & noble subject of Bot. Geograph.—11
With most sincere & hearty thanks for all your great kindness. Your’s very truly | C. Darwin
Thanks AG for the first part of his "Statistics [of the flora of the northern U. S.", Am. J. Sci. 2d ser. 22 (1856): 204–32; 2d ser. 23 (1857): 62–84, 369–403]
and for information on social and varying plants.
Would like to know number of genera of introduced plants in U. S.
Is surprised at some affinities of northern U. S. flora and asks for any climatic explanations.
Asks what proportion of genera common to U. S. and Europe are mundane.
Is glad AG will work out the northern ranges of the European species and the ranges of species with regard to size of genera.