ether Agassiz's or Hooker's views are correct; they are certainly
widely different.

Apropos to this, many thanks for the paper containing your experiments
on seeds exposed to sea water. Why has nobody thought of trying the
experiment before, instead of taking it for granted that salt water
kills seeds? I shall have it nearly all reprinted in "Silliman's
Journal" as a nut for Agassiz to crack.

LETTER 325. TO ASA GRAY. Down, May 2nd [1856?]

I have received your very kind note of April 8th. In truth it is
preposterous in me to give you hints; but it will give me real pleasure
to write to you just as I talk to Hooker, who says my questions
are sometimes suggestive owing to my comparing the ranges, etc., in
different kingdoms of Nature. I will make no further apologies about my
presumption; but will just tell you (though I am certain there will be
VERY little new in what I suggest and ask) the points on which I am very
anxious to hear about. I forget whether you include Arctic America, but
if so, for comparison with other parts of world, I would exclude the
Arctic and Alpine-Arctic, as belonging to a quite distinct category.
When excluding the naturalised, I think De Candolle must be right in
advising the exclusion (giving list) of plants exclusively found
in cultivated land, even when it is not known that they have been
introduced by man. I would give list of temperate plants (if any) found
in Eastern Asia, China, and Japan, and not elsewhere. Nothing would give
me a better idea of the flora of United States than the proportion of
its genera to all the genera which are confined to America; and the
proportion of genera confined to America and Eastern Asia with Japan;
the remaining genera would be common to America and Europe and the rest
of world; I presume it would be impossible to show any especial affinity
in genera, if ever so few, between America and Western Europe. America
might be related to Eastern Asia (always excluding Arctic forms) by a
genus having the same species confined to these two regions; or it might
be related by the genus having different species, the genus itself not
being found elsewhere. The relation of the genera (excluding identical
species) seems to me a most important element in geographical
distribution often ignored, and I presume of more difficult application
in plants than in animals, owing to the wider ranges of plants; but I
find in New Zealand (from Hooker) that the consideration of