182 - EXPERIMENT STATION. [Jan. 



The Mean Suinntei- Tcmpcralure. 



For this work we have used as a lueasiire of the sinniner heat 

 an average monthly mean for the growing season. This has 

 been taken as ciniiprising the montlis of ^lareh to September 

 inclusive. The niunthlv means for these seven months, as given 

 in publications of the United States Weather Bureau and Can- 

 adian ]\rete()rologieal Service, are averaged. This gives, for 

 ]ioints within the a])ple-growing regions of Xoi-th America, tem- 

 ]iei'a1ures varving from about 52° to about TU^ or 72^. Sum- 

 mer means have been computed for a great number of staticms, 

 and from these the isotherms given in Tig. 10 are drawn. This 

 ma}) is intended prinei})ally for study in connection Aviili llie 

 matter given later in this paper, but it may be proper to explain 

 it at this point, and to discuss the variations in the summer 

 mean that occur and the causes thereof. In connnon with other 

 questions of temperature, the sunnuer mean for a given section 

 is determined by a imniber of considerations. Among these are 

 the following: (1) latitude, (2) elevation, (3) site and as]ioct, 

 (4) soil, (5) culture, (6) prevailing winds, (7) sunshine. 



The first two require no explanation. Temperatures vary 

 inversely with the latitude and altitude, l)ut, owing to the in- 

 fluence of the other features mentioned, no ratio can be biid 

 down that is of any value. 



With regard to slope, little need be said. The sunnuer mean 

 on a noi'th slojie may be several degrees lower than that of a 

 corresponding southerly slope, though we have been unal)l(^ to 

 find any data showing the amount of difference. Slope must 

 be considered in estimating the probable temperature of an 

 orchard site. 



Soils containing a large proportion of sand will not only be 

 warmer than clayey soils, but will also influence the air temixTa- 

 ture in the orchard to a considerable degree. 



Hedrick found that the soil in a tilled orchard was from 1.1° 

 to 2.3° warmer than a corresponding ])lat in sod.^ This nnist 

 have an influence on the air temperature in ihe orchard. 



Prevailing winds influence the sunnuer mean. These are de- 



» Bulletin 314, New York Experiment Station. 



