THE RELATION OF CLIMATE TO POMOLOGY 245 



selection of a suitable location for the different varieties. 

 The heat units for each month are determined by multipl}^- 

 ing the number of days in the month by the mean monthl}' 

 temperature. In this way, the sum total of heat during the 

 season is expressed in heat units or given an index. The 

 "hottest six weeks" are also made use of, since this period is 

 considered a guide to the intensity of the summer heat.' 



Such varieties of apples as the Yellow Newtown and Esopus 

 (Spitzenburg) are conspicuously limited in their range of 

 successful production. In only a few localities are they at 

 their best, while in other places well adapted to many va- 

 rieties these two are of low quality and unreliable in their 

 behavior. Winslow shows that the Yellow Newtown requires 

 a climate possessing a long growing season, a high mean 

 summer temperature, a high total of heat units for the sea- 

 son, and it prefers a humid district where irrigation, if 

 needed at all, is only supplementary. It is pointed out that 

 other districts having similar conditions are adapted to the 

 production of this variety, but if they depart much from 

 them, the results are unsatisfactory. 



The Esopus is similar in its climatic requirements to the 

 Yellow Newtown, with the exception that irrigation sec- 

 tions are equally well adapted to its culture. 



Likewise the Winesap, which is at its best in compara- 

 tively few sections, such as the Piedmont region of Virginia 

 and the Wenatchee and Yakima valleys of Washington, re- 



^ See also Merriam, C. H. Laws of temperature control of the geo- 

 graphic distribution of terrestrial animals and plants. Nat. Geogr. 

 Mag., VI, 1894, 220-238. The formula used for determining the hottest 

 six weeks is: "multiply the monthly mean temperature of the hottest 

 month by 3, add the mean temperature of the next hottest month and 

 divide the total by 4." Example: If August monthly mean temperature 



is 68° and July 66°, then: — ^— = 67.5° temperature of the six 



hottest weeks. 



