TREES AND SHRUBS OF MEXICO. 



By Paul C. Standley. 



INTRODUCTION. 



The most interesting regions of the earth from a botanical stand- 

 point are those which possess a tropical climate. There physical 

 conditions are most favorable for the growth of plants, and not only 

 is vegetation much more luxuriant than in temperate countries, but 

 the number of species, especially of trees and shrubs, is vastly greater. 

 West Virginia and Costa Rica, for instance, are temperate and tropi- 

 cal areas of approximately equal size ; but only 1,600 species of ferns 

 and flowering plants are known from West Virginia, while the flora 

 of Costa Rica includes more than three times and probably four 

 times that number. Large areas in Mexico are neither tropical nor 

 even subtropical, but no region of the globe, probably, possesses a 

 richer or more interesting flora. Mexico has an area of 767,000 

 square miles, which, although only about one-fifth that of the United 

 States, exhibits a greater range of climatic conditions. The extremes 

 of elevation much exceed those of the United States, ranging from 

 sea level to over 5,200 meters. Almost every conceivable plant forma- 

 tion is represented — the wet tropical forests of the southern lowlands, 

 the temperate deciduous and coniferous forests of the central plateau 

 and of the ranges of the Sierra Madre, the alpine zones of the high 

 peaks like Orizaba, Popocatepetl, and Ixtaccihuatl, and the great 

 barren or cactus deserts which reach their best development in the 

 northern states. 



The botanical features of Mexico have attracted attention from the 

 days of the earliest explorers. Many botanists have visited the 

 country in the last hundred years, yet the flora is still but imper- 

 fectly known. Almost every collector at the present day makes dis- 

 coveries of remarkable species previously unknown to science, and 

 some plants are still unknown botanically although their supposed 

 medicinal properties, or their products, such as fruit, lumber, fiber, 

 and gum, are well known locally and are frequently even of com- 



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