LICHENS. 121 
Strange it seems that, while such extreme 
destitution, such sublime barrenness, prevails in 
these southern lands, in the Arctic regions, on 
the contrary, no spot has yet been discovered 
wholly destitute of vegetable life. The difference 
appears to arise more from the want of warmth 
in summer, than from the greater degree of cold 
in winter. The portion of heat imbibed by the 
soil, during the short summer of the Arctic 
regions, is prevented from escaping by the cover- 
ing of snow which falls in the beginning of win- 
ter; and thus the temperature necessary for the 
scanty vegetation is preserved, till the return of the 
sun at once converts the Arctic winter into tropi- 
cal summer, without the intervention of spring. 
Whereas in the Antarctic regions, the soil, owing 
to the much smaller quantity of snow that lies on 
it, is exposed to great alterations of temperature, 
which no vegetation, however simple and tena- 
cious of life, can long successfully resist. 
In the deserts of Asia and Africa, and on the 
coast of Peru, botanists have wandered for many 
leagues, without finding any other trace of vege- 
tation than a species of grey or yellow lichen, 
growing on the blanched and mouldering bones 
of animals that had perished by the way. In 
tropical countries, where there is not too much 
moisture and shade, the trees are shaggy with 
