422 EFFECT OF TEMPERATURE UPON FACET NUMBER 



(c) Relative Change at the Different Temperatures. — All three stocks 

 show one feature in common. The extreme high (29-31°) and low 

 (15-17.5°) temperatures produce the greatest changes in facet number 

 per °C. when the differences are expressed in per cent of the mean. 

 The lowest proportional changes are produced by the intermediate 

 temperature at or near 23° (Fig. 7). 



Except for this phenomenon of increased change at the extreme 

 temperatures, the difference in facet number accompanying a change 

 of 1°C. is roughly proportional (about 10 per cent) to the mean facet 

 number. Thus a decrease in the mean, whether produced by germi- 

 nal or environmental factors, produces a corresponding decrease in 

 the temperature increment. 



Application ofvan't Hoffs Law to Temperature Effect on Facet Number. 



Many investigators in the past 10 years have attempted to obtain 

 an expression for the relationship between temperature and the rates 

 of various biological reactions. The interest in the problem has been 

 twofold. First, in an endeavor to reduce all vital processes into terms 

 of dynamics, sorting out the physical from the chemical, the tempera- 

 ture coefficients have been compared to those of various physico- 

 chemical reactions. This has been mostly through the direct appli- 

 cation of van't Hoff's law, which for chemical reactions means a doub- 

 ling or trebling of rate for every rise of 10°C. 



The practical application of temperature effects has developed 

 another group of workers. For them van't Hoff's formula was very 

 unsatisfactory. They give a physiological interpretation and repre- 

 sent the rate of vital processes as a linear function of the temperature. 



The formula of van't Hoff and the physiological formula as given by 

 Krogh are as follows: 



where v is the velocity of the process, t is the temperature in °C., 

 Qi and Qio are the van't Hoff constants, and Ki and Kio are the Krogh 

 constants. 



