232 



POMOLOGY 



longer and hotter; the rainfall is heavier; and there is a late 

 summer or early autumn maximum. 



202. The Plains province. — The essential difference be- 

 tween the climate of the Great Plains and that of the East- 

 em province is not so much one of general temperature 

 conditions as of rainfall. The similarity of temperature 

 may be seen by comparing the summary below with that 

 given under the Eastern province. 



Table LXXII 

 temperature conditions of the plains province 



As compared with the eastern states, the Plains have 

 larger diurnal ranges of temperature; more abundant sun- 

 shine; drier air; greater evaporation; smaller rain probabil- 

 ity; less rain; more wind. The contrast in rainfall between 

 the Eastern and Plains provinces is striking. From a 20-inch 

 rainfall on the eastern margin of the Plains, it decreases to 

 below 15 inches on the western margin, and where the rain- 

 fall is below 20 inches it is insufficient for successful agricul- 

 ture, and irrigation must be practiced. 



203. The Plateau province is a great interior region of 

 very diversified topography. It has a wide range of moun- 

 tain, high plateau, and arid lowland climate, superposed on 

 and causing local modifications of the general dry continen- 

 tal climate of the province as a whole. The outstanding 

 characteristic is the small rainfall, which, however, shows 

 marked increase with altitude. With the exception of local 

 areas in the mountains, the mean annual rainfall is every- 

 where less than 20 inches; it is mostly below 10 inches, and 



