232 ENVIRONMENTAL CONDITIONS. 



(E) SUMMATIONS OF PHYSIOLOGICAL INDICES OF TEMPERATURE EFFI- 

 CIENCY FOR PERIOD OF AVERAGE FROSTLESS SEASON. (TABLE 7, 

 PLATE 40.) 



The physiological indices here employed, as indeed the summations 

 themselves, are reproduced from Livingston's paper (1916, 1) already 

 cited. For each normal daily mean within the period of the average 

 frostless season the corresponding physiological index was obtained 

 from Livingston's tabulation (our table 5, Fahrenheit scale), and all 

 the indices thus obtained were summed for each station considered. 

 The seasonal physiological indices of temperature efficiency thus 

 obtained are reproduced in column 4 of our table 7. In the same table 

 are also given the ratios of the physiological seasonal index to the 

 corresponding remainder index (above 39° F.; column 5) and to the 

 exponential seasonal index (column 6). 



The geographical distribution of the seasonal indices of temperature 

 efficiency, physiologically derived, are shown on the chart of our plate 

 40, the lines of which are reproduced from Livingston's paper (1916, 1). 

 As that writer states, the general delineation of climatic zones is here 

 much the same as in the case of the other two kinds of summations. 

 The lines again show a general west-east trend, and are again displaced 

 southward in the vicinity of the oceans (especially on the west) and of 

 the mountain systems. A cursory glance at these three charts of tem- 

 perature efficiency summations for the period of the average frostless 

 season (plates 38, 39, and 40) shows them to be so generally similar 

 that one might almost serve for either of the other two, as far as the 

 forms of the various climatic zones is concerned. Which method of 

 derivation of the efficiency indices is used seems not to be of great 

 importance in the general seasonal result. As far as present knowledge 

 goes, then, one method appears to be as satisfactory as either of the 

 others in this respect. 



The authors of these methods have discussed some of the main 

 features wherein these three charts differ in detail, and we do not need to 

 enter deeply into this matter here; but the following points may receive 

 brief mention. The actual values are much lower in the case of the 

 exponential indices (plate 39) than in either of the other cases (plates 

 40 and 41). Furthermore, the values obtained by the remainder 

 method are generally, but not always, somewhat smaller than those 

 derived from the Lehenbauer measurements for maize growth. It is 

 not possible, however, to reduce the values of one of these three series 

 to those of another, by employing any constant ratio, as is shown by 

 the variations in each of the three sets of ratio values given in table 7. 

 For convenience, we may represent the summation by the remainder 

 or difference method (above 39° F.) by D, that by the exponential or 

 chemical method by C, and that by the physiological method (based 

 on growth of maize seedlings) by G. We find (table 7) that the aver- 



