In the tundras, the most abundant vegetable forms, next to the lichens and mosses, are the grasses, the crucifers, the saxifrages, the caryophyles, and the compositæ. These grow fewer and fewer as we move towards the north, but the number of individual plants does not decrease. Where the soil is fairly dry, we shall find an extensive growth of lichens; in moister grounds, these are intermingled with the well-known Iceland moss. Lichens are everywhere, except in the sparse tracts of meadow-land lying at the foot of sheltering hills, or in those alluvial inundated hollows which are thickly planted with “whispering reeds” and dwarf willows. It is not easy to trace exactly the boundary between the tundras and the forest zone. The former descend to the south, and the latter advances to the north, according to the climatic influences which prevail; following the isothermic lines of uniform temperature, and not the mathematical limits of the geographical parallels of latitude. Where the ground undulates, and hilly ridges break the fury of the icy blasts, the forests encroach on the stony treeless region; but the desolate plains strike into the wooded zone in places where the ocean-winds range with unchecked sway. [Illustration: THE SWAMPS OF THE OBI.] The southernmost limit of the “barrens” is found in Labrador, where they descend to lat. 57°; nor is this to be wondered at, when we remember the peculiar position of that gloomy peninsula, with icy seas washing it on three sides, and cold winds sweeping over it from the north. On the opposite coasts of Hudson Bay they do not strike lower than 60°; and they continue to rise as we proceed westward, until in the Mackenzie Valley we find the tall forest growth reaching as far north as 68° or even 70°. Thence they recede gradually, until, on the bleak shore of Behring Sea, they do not rise higher than 65°. Crossing into the eastern continent, we find them beginning, in the land of the Tuski (or Tchuktche), in 63°, and from thence encroaching gradually upon the tundras until, at the Lena, they reach as high as 71°. From the Lena to the Obi the tundras gain upon the forests, and in the Obi Valley descend below the Arctic Circle; but from the Obi to the Scandinavian coast the forests gain upon the tundras, terminating, after many variations, in lat. 70°. [Illustration: IN THE FOREST ZONE OF THE NORTH.]