lustered round certain forms--that is, round
their parent-species. Undoubtedly there is one most important point of
difference between varieties and species, namely, that the amount of
difference between varieties, when compared with each other or with
their parent-species, is much less than that between the species of the
same genus. But when we come to discuss the principle, as I call it, of
divergence of character, we shall see how this may be explained, and
how the lesser differences between varieties tend to increase into the
greater differences between species.

There is one other point which is worth notice. Varieties generally have
much restricted ranges. This statement is indeed scarcely more than a
truism, for if a variety were found to have a wider range than that of
its supposed parent-species, their denominations would be reversed.
But there is reason to believe that the species which are very closely
allied to other species, and in so far resemble varieties, often have
much restricted ranges. For instance, Mr. H.C. Watson has marked for me
in the well-sifted London catalogue of Plants (4th edition) sixty-three
plants which are therein ranked as species, but which he considers as
so closely allied to other species as to be of doubtful value: these
sixty-three reputed species range on an average over 6.9 of the
provinces into which Mr. Watson has divided Great Britain. Now, in this
same catalogue, fifty-three 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
the 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.

SUMMARY.

Finally, varieties cannot be distinguished from species--except, first,
by the discovery of intermediate linking forms; and, secondly, by a
certain indefinite amount of difference between them; for two forms,
if differing very little, are generally ranked as varieties,
notwithstanding that they cannot be closely connected; but the amount
of difference considered necessary to give to any two forms the rank of
species cannot be defined. 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 lar