454 THE REGION OF PALMS. 



is no hard and fast line. Nature's operations are always 

 gradual, but nevertheless the general average limit 

 appointed for the palm tree, which forms such a con- 

 spicuous object in the tropical landscape, is plain to be 

 seen, and there it generally merges into an evergreen 

 forest of quite a distinct class of trees, which thrive 

 in the cooler atmosphere just above the region of the 

 palm. Considerably higher up again, it will be seen 

 where the evergreen forest gives place to deciduous 

 trees, whose leafless arms form a very distinct object 

 in such a landscape in winter time, and mark beyond 

 the possibility of a mistake how the increasing altitude 

 is accompanied by a constantly decreasing temperature. 

 This decrease of temperature may be fixed approxim- 

 ately at about one degree of Fahrenheit for every 300 

 feet of increased elevation ; * and in the same way we 

 may venture to assign 86 F. as the approximate 

 normal temperature of the tropical day at sea-level 

 throughout the torrid zone. But to proceed, and directing 

 our glass still further aloft, towards the mountain tops, 

 we generally find that above the region of deciduous 

 trees there comes a dark green belt of coniferous 

 forest, which is of course very distinctly marked upon 

 the hill sides; where that ends, a thin and straggling 

 belt of bush, consisting of willows and other similar 

 trees, appears, which forms the highest region of 

 arboreous vegetation (where there are no rhododendrons), 

 above which the great grass region of the higher 

 mountain slopes supplants the growth of trees entirely, 

 except were the bush runs up in sheltered hollows and 

 ravines; while above all comes the glacial region of 

 sterility, or eternal snow. Such, viewed from a dis- 



* Encycl. Brit., 9th Edition, Vol. xi., p. 829. 



