Muller has discovered several European species; other species, not introduced by man, occur on the lowlands; and a long list can be given, as I am informed by Dr.

Hooker, of European genera, found in Australia, but not in the intermediate torrid regions.

In the admirable "Introduction to the Flora of New Zealand," by Dr.

Hooker, analogous and striking facts are given in regard to the plants of that large island.

Hence, we see that certain plants growing on the more lofty mountains of the tropics in all parts of the world, and on the temperate plains of the north and south, are either the same species or varieties of the same species.