CLIMATIC RELATIONS 259 



rainfall is 1 to 3 inches less, and the proportion falling in 

 the growing season is a little less. 



At none of the Chernozem points does the yearly mean 

 reach 17 inches. Comparing this with the conditions in 

 the eastern United States, we find at Oswego a yearly 

 mean of over twice 17 inches, and at Eastport and Lynch- 

 burg over 2| times that amount. Huron has less than 

 ^ the yearly mean of Eastport, but only 4.1 inches less 

 in the growing season. Considering now, in addition, the 

 greater ability of the prairie soils to catch and retain 

 water, it is seen that the amount of water finally held 

 in the soil in the growing season may be considerably 

 greater in the semi-arid plains than in the humid region. 



At other points in the prairie regions mentioned in the 

 table, the yearly mean is greater, extending the range to 

 about 26 inches, the particular - points discussed being 

 extreme cases, and selected because of the greater con- 

 trasts offered. Nevertheless the fact remains that a large 

 part of the cereal production in the two greatest grain 

 regions of the world is grown with 16 to 26 inches annual 

 rainfall, a condition quite remarkable, and only possible 

 because of the large proportion occurring in the growing 

 season, and because of the unusual water-holding capacity 

 of the soil. 



275. The humidity of the air is a feature of climate 

 often entirely ignored, but which has a great influence 

 upon plant growth. In the relations of climate to the 

 development and maturity of the kernel, there are some 

 things not yet thoroughly understood, but the degree of 

 humidity is known to be of great importance. The influ- 

 ence of high humidity upon cereal crops is, in general, 

 unfavorable if long continued, particularly if it occurs 

 near the time of ripening. Great humidity retards 



