THE RELATION OF CLIMATE TO POMOLOGY 227 



condition usually obtains at high altitudes and the reverse 

 in valleys. High altitudes, especially in the East, may be 

 humid and, therefore, the greater freedom from disease 

 would not be found as indicated in the above statement. 

 Aside from the presence of large bodies of water, no factor 

 is so potent in causing differences in climate along any par- 

 allel of latitude as elevation above sea level. 



The facts here would seem to be contradictoiy, for there 

 is a vertical decrease of temperature with the increase in 

 elevation, amounting to about 1° F. for every 300 feet. 

 The amount of decrease of temperature will vary with the 

 latitude, exposure, season, and local conditions. But 

 what is termed "inversions of temperature" occur in clear 

 cool nights up to a certain elevation which results in the 

 higher lands being warmer than the valleys. According to 

 Hann,^ "This increase of temperature upward reaches alti- 

 tudes of at least 300 m., and is rapid in the lower strata, 

 but slower farther up." In this country the effects of these 

 inversions of temperature are experienced at practically all 

 elevations at which fruit is grown, except as noted elsewhere, 

 in certain canyons in the western United States. 



The occurrence of the colder temperatures in valleys is 

 explained by the fact that there is a radiation of heat from 

 the earth during the night and as a result the earth is cooled. 

 The stratum of air which lies next to the earth is cooled, and, 

 as cold air is heavier than warm, it results in its flowing 

 downward, and the warmer air of the valley rising. Air 

 will also lie in strata of somewhat equal temperatures, which 

 phenomenon is experienced in traveling over undulating 

 country, particularly at night. As a result of the above 

 facts, it is frequently noted that fruit blossoms (and other 

 vegetation) are injured or destroyed at lower elevations and 

 those higher up escape damage. Even the blossoms on the 

 1 Loc. cit., p. 252. 



