If, again, we anticipate that a greater variety of conditions of vegetation is the cause why the variety of vegetation, the number of species of plants, continually augments from the pole toward the equator, and that on the same account the number of sociably growing plants, of species which clothe great tracts in countless individual specimens, also increases in the same measure, we find that we are still far from being enabled to give a scientific account of the matter. It seems to us wholly the result of caprice that particular plants are distributed widely over the globe, while others must live cribbed in the narrowest spot, as, for instance, the Wulfenia, occurring exclusively on the Carinthian Alps; that particular families, like the _Compositæ_, flourish abroad over the whole earth, while others, like the peppers and the palms, only occur between very definite degrees of latitude on either side of the equator, the _Proteaceæ_ only in the Southern Hemisphere, the cactus tribe only in the western half of our earth. Just as inexplicable is the _mode of distribution_ of the families of plants. While the palms diminish in number from the equator into higher latitudes, the _Compositæ_ attain their highest development in the zones of mean temperature, their number of species diminishes from these in both directions, equally toward the equator and toward the poles; while, finally, the grasses increase constantly from the equator toward the poles. This, to us inexplicable, mode of distribution of plants according to species, genera, families, orders, and classes gives rise to certain peculiar regions on the globe, which are characterized by the predominance of certain forms of plants, or by the exclusive occurrence of particular families. These portions of the earth’s surface are called Geographical Regions of Plants, and to them have been applied the names of men who have made themselves especially famous by the investigation of these places.