244 Plant Life and Evolution 



region, and the greater richness or poverty of 

 species in different localities is due only to local con- 

 ditions. The prevailing trees, pines, hemlocks, 

 oaks, maples, elms, hickories, beeches, etc., are 

 the same everywhere, the flora naturally being richer 

 in the warmer and moister southern portions than in 

 the colder and drier northwest. The shrubs and 

 herbaceous plants are much the same throughout, of 

 course taking into account the local differences of 

 soil and exposure. 



Effect of Varying Rainfall in Jamaica. The gen- 

 eral uniformity of such a flora as that just sketched 

 has only to be contrasted with the flora of a very 

 much smaller area, where for special reasons ad- 

 jacent districts differ much in climate, especially in 

 the amount of rainfall. In Jamaica, for instance, 

 within a distance of about forty miles, mountains 

 rise to a height of over 7,000 feet, and cause the pre- 

 cipitation of most of the moisture upon one side of 

 the range, the northern side receiving from three to 

 four times as much rain as the southern side does, 

 only forty miles away. The result is that the vege- 

 tation of these two areas is more different than that 

 of Chicago and New York, nearly a thousand miles 

 apart. 



At Kingston, on the southern shore of the 

 island, the dry plains and hillsides recall our south- 

 western arid region, the prevailing plants being 

 decidedly xerophytic in character. Thus cacti, cen- 

 tury-plants, mesquit, and many other plants, belong- 



