t of species in another continent non-variable, or not
in so marked a manner. Mr. Herbert (14/2. No doubt Dean Herbert, the
horticulturist. See "Life and Letters," I., page 343.) incidentally
mentioned in a letter to me that the heaths at the Cape of Good Hope
were very variable, whilst in Europe they are (?) not so; but then the
species here are few in comparison, so that the case, even if true, is
not a good one. In some genera of insects the variability appears to be
common in distant parts of the world. In shells, I hope hereafter to
get much light on this question through fossils. If you can help me, I
should be very much obliged: indeed, all your letters are most useful to
me.

MONDAY:--Now for your first long letter, and to me quite as interesting
as long. Several things are quite new to me in it--viz., for one, your
belief that there are more extra-tropical than intra-tropical species. I
see that my argument from the Arctic regions is false, and I should not
have tried to argue against you, had I not fancied that you thought that
equability of climate was the direct cause of the creation of a greater
or lesser number of species. I see you call our climate equable; I
should have thought it was the contrary. Anyhow, the term is vague, and
in England will depend upon whether a person compares it with the United
States or Tierra del Fuego. In my Journal (page 342) I see I state that
in South Chiloe, at a height of about 1,000 feet, the forests had a
Fuegian aspect: I distinctly recollect that at the sea-level in the
middle of Chiloe the forest had almost a tropical aspect. I should like
much to hear, if you make out, whether the N. or S. boundaries of a
plant are the most restricted; I should have expected that the S. would
be, in the temperate regions, from the number of antagonist species
being greater. N.B. Humboldt, when in London, told me of some river
(14/3. The Obi (see "Flora Antarctica," page 211, note). Hooker writes:
"Some of the most conspicuous trees attain either of its banks, but do
not cross them.") in N.E. Europe, on the opposite banks of which the
flora was, on the same soil and under same climate, widely different!

I forget (14/4. The last paragraph is published in "Life and Letters,"
II., page 29.) my last letter, but it must have been a very silly one,
as it seems I gave my notion of the number of species being in great
degree governed by the degree to which the area had been often isolated
an