regions in the Caucasus lately made by Russian botanists, who have shown that the Pontic range (that is, the border-range of the Armenian plateau) is an extremely important botanic boundary, or the remarks of M. Novitskiy concerning the flora of the Karakoram plateau.
The immense region which is usually represented on geo-botanic maps under the name of Eur-Asian boreal region, and which is bounded on the south by a line traced from the Black Sea to Lake Baikal and thence to the Upper Amur and to the Sea of Okhotsk—this region has not the uniformity which one would be inclined to attribute to it by considering the map only. While it is quite certain that plants easily spread from west to east—from Russia to the lowlands of western Siberia—they spread also with the same facility from the southwest to the northeast along the high plains, the alpine zone, the border-ranges and the plateau itself. Consequently, the flora of Siberia itself can already be subdivided quite naturally into a number of distinct regions running southwest to northeast, and not west to east. Thus we see, for instance, the cedar-tree (Pinus Cembra) spreading along the highest parts of the northwestern border-range of the high plateau, from the Altai to the Lena. We find again the same vegetation on the high plateau in northwestern Mongolia, round Lake Kosogol and the Upper Vitim. The vegetation of the high plains of the Altai offers again a great analogy with the vegetation of the high plains in the west of Lake Baikal (the Minusinsk flora being an intermediate link between the two), and the Transbaikalian flora in the east of the Yablonovoi has very much in common with the flora of the Gobi.
As soon as the Amur emerges from the high plateau, in which it has excavated a deep valley, we find on its banks representatives of the Chinese and Japanese flora under the very same latitudes where we find the Siberian flora further west. And it appears from recent explorations that even round Lake Balkhash, and at the foot of the Tianshan, vestiges of the European-Siberian flora have maintained themselves on the best-watered slopes. The lines of propagation of plants along the degrees of latitude are thus completed by lines of propagation having an oblique direction, from southwest to northeast.
The next zone which is marked on our botanical maps is the zone of the Steppes, which spreads from the prairies of south Russia through the Aral-Caspian depression and the middle parts of the high plateaus.
Western and eastern Asia, including various separate desert regions (the Han-hai, the Gobi, the dry parts of Inner Arabia, of Persia and of northwest India). However, this immense region ought to be subdivided, for central Asia alone, into at least four distinct regions, namely, the Aral-Caspian flora, the Tian-shan, the Tibet and the Mongolian flora.
The flora of the regions situated on the east of the high plateau,
