u 



method. Tiiis Is based on the supposition that the growth 

 activities of niany or nioit plants stop when the temperature 

 falls to about 40" Fahrenheit. Above this temperature, 

 growth increases with increased temperature, to an optimum. 

 For convenience, the growth ra^e for 40) *> ?. may be consid- 

 ered as unit:/; them it should be 2 for 41'', 5 for 44^*, 20 for 

 oQ**, etc. If we subtract 39 degrees from anj'' given tempe- 

 rature, then, the remainder will represent, according to this 

 method, the efficiency of the temperature in question for 

 producing growth. A total efficiency value for any period 

 of time, such as the four-week growth periods of the cultures 

 of the J nvestigati on here considered, might be obtained by sub- 

 tracting 39 from each daily mean temperature and summing the 

 remainders for the period. This raefchod has frequently been 

 used in ecological studies 7/here it was desired to obtain 

 approximate expressions of temperature values in terms of 

 their efficiency to produce plant growth. 



Another method of weighting temperature values for the 

 purpose before us, and one that has an apparently more ration- 

 al basis, was suggested by Livingston and Livingston.'^ They 



V Livin?:ston, B. B. and Livingston, 9, J., '^emperatur" 

 coefficients in plant geography and climatology. Bot. Taz. 

 55:349-375.1913. 



proposed a series of temperature efficiency indices based 



on the Van't Hof f-Arrhenius law, whcih states that the velocity 



of many chemical reactions approxim.ately doubles with a rise 



