necting them with a bracket.

Those thus connected, some of them, I should in revision unite under
one, many more Dr. Hooker would unite, and for the rest it would not
be extraordinary if, in any case, the discovery of intermediate forms
compelled their union.

As I have noted on the blank page of the sheets I send you (through Sir
William Hooker), I suppose that if we extended the area, say to that of
our flora of North America, we should find that the proportion of "close
species" to the whole flora increased considerably. But here I speak at
a venture. Some day I will test it for a few families.

If you take for comparison with what I send you, the "British Flora,"
or Koch's "Flora Germanica," or Godron's "Flora of France," and mark the
"close species" on the same principle, you will doubtless find a much
greater number. Of course you will not infer from this that the two
floras differ in this respect; since the difference is probably owing to
the facts that (1) there have not been so many observers here bent upon
detecting differences; and (2) our species, thanks mostly to Dr. Torrey
and myself, have been more thoroughly castigated. What stands for one
species in the "Manual" would figure in almost any European flora as
two, three, or more, in a very considerable number of cases.

In boldly reducing nominal species J. Hooker is doing a good work;
but his vocation--like that of any other reformer--exposes him to
temptations and dangers.

Because you have shown that a and b are so connected by intermediate
forms that we cannot do otherwise than regard them as variations of one
species, we may not conclude that c and d, differing much in the same
way and to the same degree, are of one species, before an equal amount
of evidence is actually obtained. That is, when two sets of individuals
exhibit any grave differences, the burden of proof of their common
origin lies with the person who takes that view; and each case must be
decided on its own evidence, and not on analogy, if our conclusions
in this way are to be of real value. Of course we must often jump at
conclusions from imperfect evidence. I should like to write an essay on
species some day; but before I should have time to do it, in my plodding
way, I hope you or Hooker will do it, and much better far. I am most
glad to be in conference with Hooker and yourself on these matters, and
I think we may, or rather you may, in a few years settle the question as
to wh