1913] LIVINGSTON—T EMPERATURE COEFFICIENTS 361 
On the other hand, within the temperature range with which 
physiology deals, some physical phenomena exhibit temperature 
coefficients somewhat closely approximating the order of magnitude 
called for by many chemical reactions. To illustrate, the vapor 
tension of water at 4°? is 6.097 mm. of mercury, and the tensions 
at 14°, 24°, and 34° are 11.908 mm., 22.184 mm., and 39.565 
mm., respectively. Here the three temperature coefficients corre- 
sponding to these three rises of 10° in temperature are 1.95, 1.86, 
and 1.78, respectively. The vapor tension of water must be 
accounted an important condition for all transpiring plants; this 
pressure may be regarded as the driving force of evaporation, thus 
constituting the fundamental energy condition of the phenomenon 
of transpiration. 
Application of temperature coefficients to climatology 
If the processes of growth and development do really exhibit 
temperature coefficients, it is plain that the study of environmental 
integrations should deal with these rather than with temperatures 
directly. It is also plain that if direct temperature summations 
do, in certain cases, furnish adequate criteria for evaluating the 
effectiveness of temperature conditions, then this state of affairs 
must be true only within certain limits, and the experimental 
study of temperature coefficients furnishes the only adequate 
means for locating these limits and establishing the direct summa- 
tions upon a rational basis. It seems worth while, therefore, to 
make a first attempt in the direction of the application of velocity 
coefficients to the study of effective temperature conditions as these 
characterize climatic and vegetational areas. Such an attempt, of 
course, must be very unsatisfactory from an idealistic point of view; 
nevertheless, it should serve to emphasize the need of quantitative 
Studies in this connection and should also be of value in showing 
what sort of climatic and distributional observations are most 
likely to be of value as ecology becomes more exact. 
For the present study we have tentatively assumed that the 
temperature coefficient of growth and development has a value of 
2.0 for each rise of 10° C., a value which somewhat closely approxi- 
* BIEDERMAN, R., Chemicker Kalendar. 1903. Bd. 2. Berlin. 1903. pp. 84, 85. 
