230 



ENVIRONMENTAL CONDITIONS. 



Table 7. — Summation of normal daily indices of temperature efficiency for plant growth, 

 for the period of the average frostless season. (Plates 39 and 40.) — Continued. 



It is seen at once that the values given in the first column of table 7 

 are much smaller than are the corresponding ones of table 6. Living- 

 ston and Livingston made a study of the ratios obtained by dividing 

 each exponential seasonal index by the corresponding remainder index, 

 derived by using the constant difference of 39, and the resulting ratio 

 values are here reproduced in the third column of table 7. 



The chart of our plate 39 presents the climatic zonation exhibited 

 by the summations of efficiency indices derived by the application of 

 the exponential method (Van't Hoff-Arrhenius principle of chemical 

 reaction velocity), and it is essentially the same as the second chart 

 (fig. 2) of Livingston and Livingston. 



In a general way, the two charts of plates 38 and 39 agree in the 

 positions and directions of the isoclimatic lines, but they differ in a 

 number of details. A somewhat thorough comparison of these two 

 charts has been made by Livingston and Livingston, using the ratio 

 of the value of one index to that of the other (column 3 of our table 7), 

 and they present a chart of these ratios as their third figure, which we 

 do not here reproduce. As has been pointed out, these authors con- 



