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it is a point which interests me greatly.
LETTER 330. ASA GRAY TO CHARLES DARWIN. Cambridge, Mass., September
23rd, 1856.
Dr. Engelmann, of St. Louis, Missouri, who knew European botany well
before he came here, and has been an acute observer generally for twenty
years or more in this country, in reply to your question I put to him,
promptly said introduced plants are not particularly variable--are not
so variable as the indigenous plants generally, perhaps.
The difficulty of answering your questions, 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. 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 seaboard 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 north
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, fide Engelmann, is a scattered and rather scarce plant in
Germany. Here, from Boston to St. Louis, it covers the roadsides, and is
one of our most social plants. But this plant is doubtless a native of a
hotter country than North Germany.
St. John's-wort (Hypericum perforatum) is an intrusive weed in all hilly
pastures, etc., 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 South America out of the
Tropics. 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 Mountains. Fremont mentions it as the first spring food for
his cattle when he reached the western side of the Rocky Mountains. And
hardly anybody will believe me when I declare it an introduced plant. I
daresay 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
and 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 first part of my little essay on
the statistics (330/1. "Statistics of the Flora of the Northern U.S."
("Silliman's Journal," XXII. and XXIII.)) of our Northern States plants
to Trubner & Co., 12, Paternoster Row, to be thence posted to you. It
may have been delayed or failed, so I post another from here.
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,
etc.)--then some of the curious questions you have suggested--the degree
of consanguinity between the related species of our country and other
countries, and the comparative range of species in large and small
genera, etc., etc. Now, 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 and Loiseleuria procumbens. Please add them on page
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 number--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
[be] 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 northwards. The most striking case I know
is that of Convallaria majalis, in the mountains [of] Virginia and North
Carolina, and not northward. I believe I mentioned this to you before.
LETTER 331. TO ASA GRAY. Down, October 12th [1856].
I received yesterday your most kind letter of the 23rd and your
"Statistics," and two days previously another copy. 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 and works on geographical
distribution, and I know of only one essay (viz. Hooker's "New Zealand")
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" and "varying
plants," and likewise for giving me some idea about the proportion (i.e.
1/4th) 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, etc.
To return to your "Statistics." I daresay you will give how many genera
(and 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 and orders to which the
introduced plants belong. I am much interested in this, and have found
De Candolle's remarks on this subject very instructive.
Nothing has surprised me more than the greater generic and specific
affinity with East Asia than with West America. Can you tell me (and I
will promise to inflict no other question) whether climate expla |