372 PRINCIPLES OF BOTANY, ETC. 
pretty just, but mountains, valleys, rivers, marshes, 
forests, seas, and varying soil, often make a remark- 
able difference, so that some places which, accord- 
ing to the above divisions, should be warm, belong 
to the temperate or even cold climates, and vice 
versa. Wence we must make a careful distinction 
between the geographical and physical climate. 
America and Asia, though in some parts of the 
same northern latitude with us, are much colder. 
Plants which in America grow under the 42° nor- 
thern latitude, bear our climate of 52 degrees 
very well. ‘The reason of this great difference ap- 
pears to be, in America, the immense marshes and 
woody tracts; in Asia, the much more elevated and 
mountainous situation of the country. Africa is 
much hotter under the tropics, than Asia or Ame- 
rica in the same situation. But in these last coun- 
tries, immense chains of high mountains, and moist 
ground, moderate the great heat, whereas, on the 
contrary, the hot sands, of which Africa almost en- 
tirely consists, increase it. ‘The countries about the 
North Pole are much more temperate than those of 
the South Pole. The Tierra del Fuego, situated un- 
der 55° southern latitude, has a much colder cli- 
mate than Europe under 60°. High mountains, 
which with their lofty summits enter even the 
‘cloudy regions, have, in all latitudes of the globe, 
their highest points covered with ice. Cook de- 
tected such a high mountain in the Sandwich islands, 
and in America, the Andés, as they are called, under 
the tropics, are eternally covered by ice, whereas in 
the valleys beneath, a constant summer reigns. 
§ 344. 
