182 EXPERIMENT STATION. [Jan. 



The Mean Sutniner Temperature. 



For this work we have used as a measure of the summer heat 

 an average monthly mean for the growing season. This has 

 heen taken as comprising the months of March to September 

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

 in publications of the United States Weather Bureau and Can- 

 adian Meteorological Service, are averaged. This gives, for 

 points within the apple-growing regions of Xorth America, tem- 

 peratures varying from about 52° to about 70° or 72°. Sum- 

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

 and from these the isotherms given in Fig. 16 are drawn. This 

 map is intended principally for study in connection with the 

 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 wilh other 

 questions of temperature, the summer mean for a given section 

 is determined by a number of considerations. Among these are 

 the following: (1) latitude, (2) elevation, (3) site and aspect, 

 (4) soil, (5) culture, (0) prevailing winds, (7) sunshine. 



The first two require no explanation. Temperatures vary 

 inversely with the latitude and altitude, but, owing to the in- 

 fluence of the other features mentioned, no ratio can be lai<l 

 down that is of any value. 



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

 on a north slope may be several degrees lower than that of a 

 corresponding southerly slo]ie, though we have been unable to 

 find any data showing the amount of ditference. Slo]ie must 

 be considered in estimating the probable temperature of an 

 orchard site. 



Soils containing a large proporliou of sand will not only be 

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

 ture in the orchard to a considerable degree. 



Hedrick found that the soil in a tilled orchard was from l.f 

 to 2.8° warmer than a corresponding plat in sod.^ Tliis nnist 

 have an influence on the air temperature in the orchard. 



Prevailiug winds influence the summer mean. These are de- 



» Bulletin 314, New York Experiment Station. 



