he
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, will still inherit those advantages that enabled their
parents to become dominant over their compatriots.

If the plants inhabiting a country and described in any Flora be divided
into two equal masses, all those in the larger genera being placed
on one side, and all those in the smaller genera on the other side, a
somewhat larger number of the very common and much diffused or dominant
species will be found on the side of the larger genera. This, again,
might have been anticipated; for the mere fact of many species of the
same genus inhabiting any country, shows that there is something in the
organic or inorganic conditions of that country favourable to the genus;
and, consequently, we might have expected to have found in the larger
genera, or those including many species, a large proportional number of
dominant species. But so many causes tend to obscure this result, that
I am surprised that my tables show even a small majority on the side of
the larger genera. I will here allude to only two causes of obscurity.
Fresh-water and salt-loving plants have generally very wide ranges and
are much diffused, but this seems to be connected with the nature of the
stations inhabited by them, and has little or no relation to the size of
the genera to which the species belong. Again, plants low in the scale
of organisation are generally much more widely diffused than plants
higher in the scale; and here again there is no close relation to the
size of the genera. The cause of lowly-organised plants ranging widely
will be discussed in our chapter on geographical distribution.

From looking at species as only strongly-marked and well-defined
varieties, I was led to anticipate that the species of the larger genera
in each country would oftener present varieties, than the species of the
smaller genera; for wherever many closely related species (i.e. species
of the same genus) have been formed, many varieties or incipient species
ought, as a general rule, to be now forming. Where many large trees
grow, we expect to find saplings. Where many species of a genus have
been formed through variation, circumstances have been favourable
for variation; and hence we might expect that the circumstances would
generally be still favourable to variation. On the other hand, if we
look at e