CLIMATIC CONDITIONS OF THE UNITED STATES. 



245 



Probably the most generally useful of our charts of the temperature 

 conditions is the one for the length of the period of the average frostless 

 season, and the five temperature provinces just mentioned are indicated 

 on that chart (plate 34). In terms of that particular temperature 

 index, the relation between our simple names and the index values 

 is shown in table 9. For other temperature indices the values would 



Table 9. 



of course be entirely different, but the general zonation for these other 

 indices may be generally comparable to that of plate 34, if proper 

 limiting values are chosen. In the case of the temperature summation 

 indices obtained by the physiological method (plate 40 and fig. 1), for 

 example, the zones noted in table 10, roughly comparable to those 



Fig. 1. — Temperature zonation, according to physiological summations for period of average frostless 

 eeason. Temperature efficiency provinces: very warm, more than 20; warm, 12.5 to 20; medium, 

 7.5 to 12.5; cool, 2.5 to 7.5; uery cool, less than 2.5. Numerical values represent thousands. (See 

 also plate 40.) 



