COLD TEMPERATE WOODLAND AND GRASSLAND 543 



is so small in the cold temperate belt of the southern hemisphere that 

 it need hardly be considered. 



2. FOREST AND PRAIRIE IN THE UNITED STATES 

 OF NORTH AMERICA. 



The United States of North America, when regarded from the point of 

 view of their atmospheric precipitations, show a distinction into four chief 

 districts proceeding from east to west 1 : — 



District without a dry season. In this, the Atlantic district, rain falls 

 abundantly at all seasons of the year, with a perceptible maximum in 

 summer. Near the coast the precipitation is about 1,000 mm. annually; in 

 the south and bordering on the Gulf of Mexico, 1,200 mm. ; to the west pre- 

 cipitation descends to 800 or 900 mm. The western limit of the district is 

 approximately fixed by the Mississippi. 



District with dry winters and moist early summers. This district lies to 

 the west of the Mississippi and extends up to the base of the Rocky Moun- 

 tains. The precipitation is less than in the Atlantic district and attains 

 from 500 to 600 mm. ; it decreases from east towards the west. 



District with a very scanty rainfall. This district forms the plateau 

 situated between the Rocky Mountains and the Sierra Nevada, and has 

 nearly everywhere a rainfall of 300 mm. or less, the precipitations either 

 occurring throughout the year or failing almost completely during the height 

 of summer. 



District with winter-rain. This lies on the Pacific coast to the west of 

 the Sierra Nevada (Washington, Oregon, California). In the north precipi- 

 tation is very abundant and the summer also is moist, although much less 

 so than winter. To the south the precipitation is less (about 500 mm.) and 

 summer is rainless ; the most southern part of California receives only 

 a very scanty precipitation (about 250 mm.). 



The character of the vegetation of all four districts can be accurately anti- 

 cipated from the quantity and especially from the seasonal distribution of 

 the precipitations : — 



The Atlantic district, with precipitations not only frequent but also taking 

 place during winter, has a true forest climate, and is, in fact, covered with 

 forests which decrease in height and in luxuriance towards the north-west, 

 just as the rainfall diminishes. In the southern part with mild winters, the 

 forests are hygrophilous (subtropical rain-forest) ; in the north, corresponding 

 to the cold winters, they are tropophilous. 



1 According to Greely meteorologists distinguish thirteen types. For the questions 

 before us such a detailed classification is unnecessary. 



