1913] LIVINGSTON—TEMPERATURE COEFFICIENTS 375 
ing to find out; it obviously has to do with the order of magnitude 
of the normal daily mean temperatures and also with the distri- 
bution of these magnitudes throughout the mean frostless season. 
There seems little doubt that a mathematical treatment involving 
limits may bring out the nature of those characteristics of the 
frostless season which are measured by the ratio as employed in 
this paper. 3 
Conclusions 
1. The method of direct temperature summations has proved 
itself to give, in a broadly general way and for most of the area of the 
United States, nearly the same climatic zones as does our method of 
efficiency summations; for practical purposes and for the present, 
the former method, till now based solely on phenological observa- 
tions, seems thus to be placed in closer logical connection with the 
temperature coefficients of chemical, physical, and physiological 
processes than has heretofore been the case. 
2. The similarity between the results derived by these two 
methods of temperature integration, however, is only superficial 
and roughly approximate. The ratios of direct summation to 
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. 
3. A rational and consistent climatic chart represents the 
geographical distribution of these ratio values; on such a chart the 
marginal regions of the country are frequently characterized by low 
ratios and the two main mountain systems appear to control areas 
of high values. 
4. There seems to be no doubt that the ratio here brought 
forward quantitatively represents a climatic dimension or charac- 
teristic, which appears to be some sort of function of the daily 
normal temperatures upon which this whole study has been based 
and of the time distribution of these temperature data within the 
period of the mean frostless season. 
LaBorATORY oF PLANT PHYSIOLOGY 
Jouns Hopkins UNIVERSITY 
