CLIMATIC CONDITIONS OF THE UNITED STATES. 231 



elude from their study of these two methods of estimating temperature 

 effectiveness that the method that derives efficiency indices by sub- 

 tracting 39 from each daily mean temperature index gives, "in a 

 broadly general way, and for most of the area of the United States, 

 nearly the same climatic zones" {loc. cit, p. 375) as those given by 

 summations of temperature efficiencies based on the chemical coeffi- 

 cient of 2.0. Nevertheless, these authors point out that ''the similarity 

 between the results derived by these two methods of temperature 

 integration is, however, only superficial and roughly approximate. 

 The ratios of direct summation (above 39° F.) to chemical efficiency 

 summation, range in magnitude, for the mean frostless season in the 

 United States, from a minimum of 7.49 to a maximum of 10.44." 

 Their chart (fig. 3) shows clearly that these ratio values (column 3 of 

 our table 7) are to be considered as some sort of chmatic measure. The 

 marginal regions of the United States are frequently characterized by 

 low ratio values and the two main mountain systems seem to have 

 high ratio values. For most of the area of the country the ratio of the 

 summation index derived by the method of subtraction, to the index 

 derived from the chemical coefficient, has a value of about 9.5, and the 

 assumption of this as a constant ratio between the two indices does not 

 introduce very large errors for most of the area with which we are 

 dealing. 



The feature of these chemical efficiency indices that should attract 

 our attention, however, is their relative values; according to the funda- 

 mental assumptions upon which these efficiency indices are based, 

 these values should be proportional to the amounts of plant accom- 

 phshment within the frostless season, at the corresponding locahties. 

 Thus, referring to plate 40, if plant production in the region of East- 

 port, Maine, has a value of 300 for the average frostless season at that 

 station, that in the vicinity of Jacksonville, Florida, should have a 

 value of 1,000 for the frostless season there. The extreme range of this 

 seasonal temperature efficiency, as shown by the chart of plate 39 and 

 by table 7, column 2, is from 276 (Sault Ste. Marie, Michigan) to 1,538 

 (Key West, Florida), or from unity to about 5.6. By the remainder 

 indices (plate 38, table 6), the corresponding range is from 3,543 to 

 17,077, or from unity to about 4.8. It is thus brought out that, while 

 one method of deriving efficiency indices would lead us to expect only 

 4.8 times as much plant activity at Key West as at Sault Ste. Marie, 

 the other would lead us to expect this ratio to have the value 5.6. Since 

 the physiological indices of temperature efficiency promise to be much 

 more valuable in climatological study than either of the kinds of 

 indices so far applied in our study, we need not here enter further into 

 this comparison. 



