umber 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.

SPECIES OF THE LARGER GENERA IN EACH COUNTRY VARY MORE FREQUENTLY THAN
THE SPECIES OF THE SMALLER GENERA.

If the plants inhabiting a country as described in any Flora, be divided
into two equal masses, all those in the larger genera (i.e., those
including many species) being placed on one side, and all those in the
smaller genera on the other side, the former will be found to include a
somewhat larger number of the very common and much diffused or dominant
species. This 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
larger 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
generally have 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
smal