PRACTICAL STUDY OF PLANT FORMATIONS. 647 



limes, and shaddocks) are grown successfully in the warmer parts, par- 

 ticularly in peninsular Florida, but in the northern parts have suffered 

 severely from frosts." 



THE TROPICAL REGION. "The tropical region within the United States 

 is of small extent and is restricted to three widely separated localities 

 southern Florida, extreme southeast Texas (along the lower Rio Grande 

 and Gulf coast), and the valley of the lower Colorado River in Arizona 

 and California. The Florida area is genuine humid tropical; the Texas 

 and Arizona-California areas are dilute arid tropical. Among the tropical 

 trees that grow in southern Florida are the royal palm, Jamaica dogwood, 

 manchirieel, mahogany, and mangrove. . . . The extension of the arid 

 tropical along the lower Colorado and Gila rivers is over a desert region 

 of excessive aridity. . . . The flora has not been sufficiently studied, but is 

 characterized by giant cactuses, desert acacias, palo verdes, and the Wash- 

 ington or fan-leaf palm. 



"With irrigation the arid tropical areas are found to be as productive 

 as the humid tropical, but they have been cultivated so short a time that 

 their capabilities can only be inferred from the circumstance that bananas, 

 citrons, dates, guavas, lemons, loquates, oranges, and Mexican limes do 

 well in the Arizona-California arm. No information is at hand relating 

 to the Texan or Tamaulipan arm." 



