CHAPTER II
VARIATION UNDER NATURE
Wide-ranging, much diffused, and common Species vary most
Guided by theoretical consideration, I thought that some interesting
results might be obtained in regard to the nature and relations of the
species which vary most, by tabulating all the varieties in several
well-worked floras. At first this seemed a simple task; but Mr. H.
C. Watson, to whom I am much indebted for valuable advice and
assistance on this subject, soon convinced me that there were many
difficulties, as did subsequently Dr. Hooker, even in stronger
terms. I shall reserve for a future work the discussion of these
difficulties, and the tables of the proportional numbers of the
varying species. Dr. Hooker permits me to add that after having
carefully read my manuscript, and examined the tables, he thinks
that the following statements are fairly well established. The whole
subject, however, treated as it necessarily here is with much brevity,
is rather perplexing, and allusions cannot be avoided to the "struggle
for existence," "divergence of character," and other questions,
hereafter to be discussed.
Alphonse de Candolle and others have shown that plants which have
very wide ranges generally present varieties; and this might have been
expected, as they are exposed to diverse physical conditions, and as
they come into competition (which, as we shall hereafter see, is an
equally or more important circumstance) with different sets of organic
beings. But my tables further show that, in any limited country, the
species which are the most common, that is abound most in individuals,
and the species which are most widely diffused within their own
country (and this is a different consideration from wide range, and to
a certain extent from commonness), oftenest give rise to varieties
sufficiently well marked to have been recorded in botanical works.
Hence it is the most flourishing, or, as they may be called, the
dominant species,- those which range widely, are the most diffused
in their own country, and are the most numerous in individuals,- which
oftenest produce well-marked varieties, or, as I consider them,
incipient species. And this, perhaps, might have been anticipated; for
as varieties, in order to become in any degree permanent,
necessarily have to struggle with the other inhabitants of the
country, the species which are already dominant will be the most
likely to yield offspring, which, though in some slight degree
modified, still inherit those advantages that enabled their parents to
become dominant over their compatriots. In these remarks on
predominance, it should be understood that reference is made only to
the forms which come into competition with each other, and more
especially to the members of the same genus or class having nearly
similar habits of life. With respect to the number of individuals or
commonness of species, the comparison of course relates only to the
members of the same group. One of the higher plants may be said to
be dominant if it be more numerous in individuals and more widely
diffused than the other plants of the same country, which live under
nearly the same conditions. A plant of this kind is not the less
dominant because some conferva inhabiting the water or some
parasitic fungus is infinitely more numerous in individuals and more
widely diffused. But if the conferva or parasitic fungus exceeds its
allies in the above respects, it will then be dominant within its
own class.
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