12 The Principles of Fruit-growing 



The annual temperature of a region is chiefly deter- 

 mined by four factors, the latitude, the altitude, the 

 physical configuration, and the proximity or remoteness 

 of large bodies of water. 



The moisture determinant. 



The second chief factor of climate in determining the 

 fruit-zones is relative humidity. Whilst the isotherms 

 or lines of equal temperatures run easterly and westerly, 

 the isohyetals or lines of equal rainfall have no in- 

 trinsic direction. They are determined by physiographical 

 features. In the United States, we might recognize 

 very roughly six general fruit-zones marked by pecu- 

 liarities of rainfall. These are the Atlantic zone, a moist 

 area bounded westward approximately by the Mississippi 

 River; the Plains zone, extending westward to the Rocky 

 Mountains, mostly of low rainfall and in some parts semi- 

 arid; the inter-mountain region, being mostly arid and 

 requiring irrigation; the Sonoran zone of New Mexico 

 and Arizona and southward; the California region, mostly 

 arid and semi-arid; the upper Pacific region, comprising 

 the humid belt of Oregon, Washington, and British Colum- 

 bia. Within all these regions are geographical areas of 

 special precipitation conditions. The interior or plains 

 region is particularly trying to fruits because of the strong 

 and dry winter winds, which evaporate the moisture from 

 the trees while the ground is often so deeply frozen that 

 the roots cannot supply moisture. There is probably 

 always evaporation from tree tops in the winter when the 

 air is drier than the wood. The fact that moisture may be 

 lost from winter twigs is a most important consideration 

 in the study of the winter injury of trees, and it throws 

 light upon the severe damage that often follows the "dry 



