Periodical Literature. 421 



An unprecedented amount of frost damage occurred in the 

 winter of 1911-12, especially with trees standing in openings. 

 The explanation offered is that the mild, wet autumn left the 

 trees in poor condition to withstand the cold winds of winter. 



K. W. W. 



Verhalten erwacluener Pichten gegen Diirrc iind Frost. Forstwissen- 

 schaftliches Centralblatt. December, 1912. Pp. 600-60;. 



SOIL, WATER AND CLIMATE. 



In a very thoughtful and interesting article 

 Forests JMr. Zon discusses on broad lines forest 



and influences and tries especially to establish a 



Rainfall. specific relation between the forest cover 



of the southern forest areas and the hu- 

 midity and rainfall conditions of the central States and prairie 

 region. The argument is based on the fact that the prevailing 

 winds which bring precipitation to the central States and, indeed, 

 the entire Eastern half of the United States, are southerly; on 

 the assertion that seven ninths of the precipitation is furnished 

 not by oceans but by evaporation from the land ; and on the ob- 

 servation that forests evaporate more water than any other 

 vegetative cover or free water surfaces. 



The north-south direction of the mountain ranges permits the 

 southern winds to carry their influence far north, while the rapid 

 decrease in temperatures from south to north — more rapid than 

 in Europe — also plays a role in causing precipitation. The winds 

 from the west and northwest during winter, fall and early spring 

 are dry and either cold or hot, but the south winds prevail dur- 

 ing summer and are moisture laden, and are responsible for 

 precipitation, as they blow into colder air. 



"If precipitation over land depended only on the amount of 

 water directly brought by the prevailing humid winds from 

 the ocean, the land would be pretty arid and rainfall would be 

 confined to only a narrow belt close to the ocean. * Fortunately, 

 not all the water that is precipitated is lost from the air-currents ; 

 a part runs off into the rivers or percolates into the ground, but a 

 large part of it is again evaporated into the atmosphere 



* This is not a necessary sequel ! 



