ver
case. How I wish I knew what plants the clover took the place of; but
that would require more accurate knowledge of any one piece of ground
than I suppose any one has. In the case of trees being so long-lived, I
should think it would be extremely difficult to distinguish between true
and new spreading of a species, and a rotation of crop. With respect to
your idea of plants travelling west, I was much struck by a remark of
yours in the penultimate "Linnean Journal" on the spreading of plants
from America near Behring Straits. Do you not consider so many more
seeds and plants being taken from Europe to America, than in a reverse
direction, would go some way to account for comparative fewness of
naturalised American plants here? Though I think one might wildly
speculate on European weeds having become well fitted for cultivated
land, during thousands of years of culture, whereas cultivated land
would be a new home for native American weeds, and they would not
consequently be able to beat their European rivals when put in contest
with them on cultivated land. Here is a bit of wild theory! (342/1.
See Asa Gray, "Scientific Papers," 1889, Volume II., page 235, on "The
Pertinacity and Predominance of Weeds," where the view here given is
adopted. In a letter to Asa Gray (November 6th, 1862), published in the
"Life and Letters," II., page 390, Darwin wrote: "Does it not hurt your
Yankee pride that we thrash you so confoundedly? I am sure Mrs. Gray
will stick up for your own weeds. Ask her whether they are not more
honest downright good sort of weeds.")

But I did not sit down intending to scribble thus; but to beg a favour
of you. I gave Hooker a list of species of Silene, on which Gartner has
experimentised in crossing: now I want EXTREMELY to be permitted to say
that such and such are believed by Mr. Bentham to be true species, and
such and such to be only varieties. Unfortunately and stupidly, Gartner
does not append author's name to the species.

Thank you heartily for what you say about my book; but you will be
greatly disappointed; it will be grievously too hypothetical. It will
very likely be of no other service than collocating some facts; though
I myself think I see my way approximately on the origin of species. But,
alas, how frequent, how almost universal it is in an author to persuade
himself of the truth of his own dogmas. My only hope is that I certainly
see very many difficulties of gigantic stature.

If y