From Asa Gray 23 September 1856
Sept. 23d. 1856.
My Dear Mr. Darwin
Dr. Engelmann,1 of St. Louis, Missouri—who knew European botany well before he came here, and has been an acute observer generally for 20 years or more in this country, in reply to your question I put to him, promptly said that introduced plants are not particularly variable—are not so variable as the indigenous plants generally, perhaps.
The difficulty of answering your question, as to whether there are any plants social here, which are not so in the old world,—is, that I know so little about European plants in nature.2 The following is all I have to contribute. Lately I took Engelmann and Agassiz on a botanical excursion over half a dozen miles of one of our sea-board counties; when they both remarked that they never saw in Europe altogether half so much Barberry as in that trip. Through all this district B. vulgaris may be said to have become a truly social plant, in neglected fields and copses, and even penetrating into rather close old woods. I always supposed that birds diffused the seeds. But I am not clear that many of them touch the berries. At least these hang on the bushes over winter in the greatest abundance. Perhaps the barberry belongs to a warmer country than N. of Europe, and finds itself more at home in our sunny summers. Yet out of New England it seems not to spread at all.
Maruta Cotula,3 fide Engelmann, is a scattered & rather scarce plant in Germany. Here, from Boston to St. Louis, it covers the road-sides, and is one of our most social plants. But this plant is doubtless a native of a hotter country than N. Germany.
St. Johns-wort (H. perforatum) is an intrusive weed in all hilly pastures, &c.—and may fairly be called a social plant. In Germany it is not so found, fide Engelmann.
Verbascum Thapsus is diffused over all the country,—is vastly more common here than in Germany, fide Engelmann.
I suppose Erodium cicutarium was brought to America with cattle from Spain; it seems to be widely spread over S. America out of tropics—&c In Atlantic U.S. it is very scarce and local. But it fills California and the interior of Oregon, quite back to the west slope of the Rocky Mts.— Fremont mentions it as the first spring food for his Cattle when he reached the Western side of the Rocky Mts.—4 And hardly any body will believe me when I declare it an introduced plant. I dare say it is equally abundant in Spain. I doubt if it is more so.
Engelmann and I have been noting the species truly indigenous here which, becoming ruderal or campestral, are increasing in the number of individuals instead of diminishing, as the country becomes more settled & forests removed.— The list of our wild plants which have become true weeds is larger than I had supposed, and these have probably all of them increased their geographical range—at least, have multiplied in numbers in the Northern States, since settlements.—
Some time ago I sent a copy of the 1st part of my little essay on the Statistics of our N. States plants to Trübner & Co. 12, Pater Noster Row, to be thence posted to you.5 It may have been delayed or failed, so I post another from here. I regret that I can[not] prepay on U.S. postage on pamphlets.— So I suppose it will cost you 6d—at least, and be an unnecessary expence.
This is only a beginning. Range of species in latitude must next be tabulated,—disjoined species catalogued, (i.e. those occurring in remote and entirely separated areas,—e.g. Phryma, Monotropa uniflora &c.—N. American & Himalayan.)—then some of the curious questions you have suggested.—the degree of consanguinity between the related species of our country & other countries, &c and the comparative range of species in large & small genera, &c &c &c So is it worth while to go on at this length of detail?— There is no knowing how much space it may cover. Yet after all facts in all their fullness is what is wanted—and those not gathered to support (or even to test) any foregone conclusions. It will be prosy; but it may be useful.
Then I have no time properly to revise mss. and correct oversights.— To my vexation, in my short list of our alpine species I have left out, in some unaccountable manner, two of the most characteristic, viz. Cassiope hypnoides & Loiseleuria procumbens. Please add them, on p. 28.—
There is much to be said about our introduced plants—
But now, and for some time to come, I must be thinking of quite different matters.— I mean to continue this essay in the January no.—for which my mss. must be ready about the 1st of November.—
I have not yet attempted to count them up; but of course I am prepared to believe that fully three fourths of our species common to Europe will found to range northward to the arctic regions, I merely meant that I had in mind a number that do not; I think the number will not be very small: and I thought you were under the impression that very few absolutely did not so extend northward.6
The most striking case I know is that of Convallaria majalis, in the Mts. Virginia & N. Carolina—and not northward— I believe I mentioned this to you before—
By the way Guyot, who is reliable has newly measured the height of Black Mts, of North Carolina, and makes it higher than I supposed. He had satisfactory data, he says (barometric), and makes it summit 6700 feet!7 It should have alpine vegetation, one would think, but I know not a single truly alpine phænogamous plant there.
Yours most faithfully Asa Gray
I suppose the sea is not harmful to you. As to quietness if you will come over for a holiday, you shall be as quiet here as in Kent, and could travel about the country very leisurely.
Plants that are social in the U. S. but are not so in the Old World.
Distribution of U. S. species common to Europe.
Gives Theodor Engelmann’s opinion on the relative variability of indigenous and introduced plants and notes the effects of man’s settlement on the numbers and distribution of indigenous plants.