y, to compare the list of European plants in Tierra del Fuego
(in Hooker) with those in North America; for, without multiple creation,
I think we must admit that all now in T. del Fuego must have travelled
through North America, and so far they do concern you.

The discussion on social plants (vague as the terms and facts are) in
De Candolle strikes me as the best which I have ever seen: two points
strike me as eminently remarkable in them; that they should ever be
social close to their extreme limits; and secondly, that species having
an extremely confined range, yet should be social where they do occur: I
should be infinitely obliged for any cases either by letter or publicly
on these heads, more especially in regard to a species remaining or
ceasing to be social on the confines of its range.

There is one other point on which I individually should be extremely
much obliged, if you could spare the time to think a little bit and
inform me: viz., whether there are any cases of the same species being
more variable in United States than in other countries in which it
is found, or in different parts of the United States? Wahlenberg says
generally that the same species in going south become more variable than
in extreme north. Even still more am I anxious to know whether any of
the genera, which have most of their species horribly variable (as
Rubus or Hieracium are) in Europe, or other parts of the world, are less
variable in the United States; or, the reverse case, whether you have
any odious genera with you which are less odious in other countries? Any
information on this head would be a real kindness to me.

I suppose your flora is too great; but a simple list in close columns in
small type of all the species, genera, and families, each consecutively
numbered, has always struck me as most useful; and Hooker regrets that
he did not give such list in introduction to New Zealand and other
Flora. I am sure I have given you a larger dose of questions than you
bargained for, and I have kept my word and treated you just as I do
Hooker. Nevertheless, if anything occurs to me during the next two
months, I will write freely, believing that you will forgive me and not
think me very presumptuous.

How well De Candolle shows the necessity of comparing nearly equal areas
for proportion of families!

I have re-read this letter, and it is really not worth sending, except
for my own sake. I see I forgot, in beginning, to state that