20 STUDIES ON FRUIT RESPIRATION. 



As was foreseen from the study of the literature, a rise in tem- 

 perature was accompanied by a very rapid increase of respiratory 

 activity, and, as the data accumulated, the general resemblance of 

 the curves to each other became increasingly evident. There seemed 

 to be some general law regulating the increase of respiration with 

 temperature. At this point, material assistance was received from 

 C. S. Hudson, of this bureau. The curve under consideration at the 

 time was that of Delaware grapes. The values at the four different 

 temperatures are given in Table 1 and graphically represented in fig. 

 9. At Mr. Hudson's suggestion, besides plotting the actual values 

 found for the carbon dioxid per hour per kilogram of fruit, the loga- 

 rithm of the carbon dioxid figure was used, and the points were found 

 to lie nearly in a straight line. The equation of this line by con- 

 struction is — 



log(C0 2 )« = log(C0 2 W + a* 



or if (CO,)* = y and (CO 2 ),= ° = y , then 



log y = log i/ + at (Equation 1 . ) 



Logarithm y and a 1 may be readily determined by inspection; 2 log y Q 

 (the intercept on the y axis) equals 0.78, and 30a equals 1.790 — log y OJ 

 equivalent to 1.010, therefore a equals 0.0337. 



The location of the straight line most nearly representing the facts 

 is more or less empirical and a number of circumstances must be con- 

 sidered. A small error in the determination of the activity at low 

 temperatures affects the results when plotted as the logarithm 

 much more than the same numerical error at higher temperatures. 

 Hence less weight should be given to the cold-storage values than to 

 the others. With many fruits the activity has been found to decline 

 when held at high temperatures. For this reason less consideration 

 should be given to the data obtained at incubator temperature than 

 to those obtained from fruit kept at refrigerator and at room tem- 

 peratures. While certain inaccuracies are thus unavoidable, this 

 method of expressing the results has been found of great value in 

 comparing the different fruits with one another. The results obtained 

 by plotting the data in this way are given graphically in figs. 10 to 14, 

 inclusive. 



From equation 1, written in the -exponential form y=y o 10 at , it is 

 possible to calculate the number of times that y will be increased for 

 any given rise in temperature. If the activity is y' at temperature t', 

 at t" the activity y" = y'\W'-v. If t" -V = 10° C, i/"=-i/'10 100 . 

 The number whose logarithm is 10a is the number of times by 

 which the activity is increased for 10° C. 



1 The constant a is defined on p.' 24. 2 See fig. 9. 



