428 



THE POPULAR SCIENCE MONTHLY 



product of the number of hours the plant stood above the temperature 

 at which growth began and of the averaged intensities during this 

 period. The method was obviously empirical, as it assumed that the 

 rate of growth was the same at all temperatures above its zero point, 

 which might be freezing or above it. 



Temp. 35 40 45 50 55 60 65 70 75 80 85 90 95 100 110 Fan r. 



Fig. 6. Graph Showing Rate of Growth of Seedlings of Wheat at Tem- 

 feeatures Between 40° and 108° P., plotted from data given in text-books of plant 

 physiology. 



Next, Professor B. E. Livingston, using the exponential law of chem- 

 ical velocity in the interpretation of temperature effects, found that 

 survival and distribution of some types of vegetation were explainable 

 upon the temperature integrations arrived at in this manner. This 

 method, however, still depends upon averages or summations of tem- 

 perature and does not evaluate the higher temperatures correctly as the 



