694 INFLUENCE OF CLIMATE 



How striking is the contrast between the bota- 

 nical and zoological character of these different 

 zones. The first abounds with palms, bananas, 

 sugar, coffee, myrtles, pomegranates, and aro- 

 matic spices ; the second, with oranges, limes, 

 figs, maize, rice, olives, grapes, and other delici- 

 ous fruits : while the third is the favourite region 

 of the grasses, wheat, barley, rye, oats, and a 

 variety of forest trees, not found in tropical and 

 warm climates, nor in the regions of perpetual 

 cold, where only a few species of low cryptoga- 

 mous plants are produced. In accordance with 

 the foregoing facts, it has been shown by Hum- 

 boldt, that the strength and continuance of vege- 

 gation are in proportion as the temperature rises 

 above 52, below which, it is arrested in all cli- 

 mates ; and that the number of vegetable species 

 in the tropical, temperate, and polar latitudes, is 

 in the ratio of 1 2, 4, and 1 ; so that the growth of 

 vegetation may be regarded as a natural thermo- 

 meter on a grand scale. 



But as all animals are nourished by plants, or 

 by animals that have lived on plants, it is clear 

 that the capacity of any country to support a 

 numerous and wealthy population, must depend 

 chiefly on climate. For example, throughout the 

 whole of Asia and North America, above latitude 

 50, the mean annual temperature is below o2, 

 and the growth of vegetation is arrested for ten or 

 eleven months in the year, while in the coldest 



