THE POLAR ZONE. 177 



which are found to approach nearest the limit 

 of perpetual snow are the dwarf birch, (Betula 

 nana,) and the dwarf willow, ($Q&c herbacea,) 

 though they are so small that they can scarcely 

 be denominated trees. The dwarf birch seldom 

 exceeds two or threeJfeet in height, though it 

 is said that at the island of Hammerfest, lat. 

 70 40', in the sheltered hollows, it rises to the 

 height of a man. In Lapland, at the height of 

 two thousand five hundred feet, it finds just 

 sufficient warmth about the end of June to put 

 forth three leaves from each bud, which, in a 

 few weeks, wither and fall off again ; but this 

 feeble effort suffices to preserve the life of the 

 plant. In Asiatic Siberia^ north of 60, the 

 ground is perpetually frozen at a very small 

 depth below the surface ; a temperature of 70 

 below zero is not uncommon, and in some in- 

 stances it has been 120. Then it is fatal to 

 animal life, especially if accompanied with wind. 

 In Nova Zembla, the vegetation is so stunted 

 that it barely covers the ground. The woody 

 plants, such as the dwarf birch and the reticu- 

 lated willow, (Saliv reticulata,) with a very few 

 berry-bearing shrubs, trail along the ground, 

 never rising more than an inch or two above it. 

 The woolly-leaved willow (Salia lanatd) is the 

 giant of these northern forests, though it never 

 grows more than five inches above the surface, 

 while its trailing stem, ten or twelve feet long, 

 lies hid among the moss. 



8. The Polar Zone, including all above 72 

 of N. lat. to the pole. No trees or bushes grow 



