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.

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