provinces into which
Mr. Watson has divided Great Britain. Now, in this same catalogue, 53
acknowledged varieties are recorded, and these range over 7.7 provinces;
whereas, the species to which these varieties belong range over 14.3
provinces. So that the acknowledged varieties have very nearly the same
restricted average range, as have those very closely allied forms, marked
for me by Mr. Watson as doubtful species, but which are almost universally
ranked by British botanists as good and true species.

Finally, then, varieties have the same general characters as species, for
they cannot be distinguished from species,--except, firstly, by the
discovery of intermediate linking forms, and the occurrence of such links
cannot affect the actual characters of the forms which they connect; and
except, secondly by a certain amount of {59} difference, for two forms, if
differing very little, are generally ranked as varieties, notwithstanding
that intermediate linking forms have not been discovered; but the amount of
difference considered necessary to give to two forms the rank of species is
quite indefinite. In genera having more than the average number of species
in any country, the species of these genera have more than the average
number of varieties. In large genera the species are apt to be closely, but
unequally allied together, forming little clusters round certain species.
Species very closely allied to other species apparently have restricted
ranges. In all these several respects the species of large genera present a
strong analogy with varieties. And we can clearly understand these
analogies, if species have once existed as varieties, and have thus
originated: whereas, these analogies are utterly inexplicable if each
species has been independently created.

We have, also, seen that it is the most flourishing or dominant species of
the larger genera which on an average vary most; and varieties, as we shall
hereafter see, tend to become converted into new and distinct species. The
larger genera thus tend to become larger; and throughout nature the forms
of life which are now dominant tend to become still more dominant by
leaving many modified and dominant descendants. But by steps hereafter to
be explained, the larger genera also tend to break up into smaller genera.
And thus, the forms of life throughout the universe become divided into
groups subordinate to groups.

* * * * *

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