To Asa Gray 14 July 1
Down Bromley Kent
My dear Dr Gray
You have been so very kind in giving me information of the greatest use to me;2 that I venture to trouble you with a question, which cannot cause you much trouble.— I have been reading a paper by you on plants on mountains of Carolina, (in London Journal of Botany)3 in which you state that most are the same with the plants of the N. States & Canada.— Now what I want to know is, whether the Alleghenies are sufficiently continuous so that the plants could travel from the north in the course of ages thus far south?4 I remember Bartram makes the same remark with respect to several trees on the Occone Mts ,—not that I know where these Mountains are.—5
How does your memoir on Geograph. Distrib. get on?6 I do heartily wish it was now published; for I have been trying to make out how many plants are common to Europe, which do not range up to the Arctic shores, & they seem to be very few.—
I have just thought of one other question, connected with my subject, which I cannot resist asking.— I have seen it remarked by entomologists, that it often happens that the intermediate varieties connecting together two varieties (& thus showing that such are varieties) are less common or numerous in individuals, than the two varieties themselves.7 If you can enlighten me on this head I shd be very much obliged. I am inclined to think there must be some truth in it; otherwise varieties would not be so well marked as they often are.— I wrote some time ago, a troublesome letter, in which I begged for information on the amount of variability of your naturalised & your agragrian plants, as compared with other species of the same genera.—8
But I know I have been scandalously troublesome to you.— Can you forgive me? & believe me, Yours truly obliged | Ch. Darwin
Asks whether Allegheny Mountains are sufficiently continuous so that plants could travel from north to south along them.
Hopes AG’s work on geographical distribution is progressing, as he has questions on plants common to Europe which do not range up to Arctic.
Are intermediate varieties less numerous in individuals than the varieties they connect?
Please cite as
Darwin Correspondence Project, “Letter no. 1926,” accessed on 22 February 2017, http://www.darwinproject.ac.uk/DCP-LETT-1926