314 BOTANICAL GAZETTE [octobeb 



when the wide variation in size, thickness of epidermis, etc., is 

 considered. The extremes of variation found in apples held at 

 20° C. are indicative of the range of fluctuation that may be 

 encountered in work of this type. The 31 apples analyzed at this 

 temperature contained gas averaging 17.2 per cent C0 2 . The 

 minimum C0 2 recorded for any apple of the lot was 12.5 per cent; 

 the maximum 25.7 per cent. Only one apple, however, showed 

 more than 21.8 per cent, so that this latter figure is a more accurate 

 maximum. The extremes of oxygen variation were somewhat less. 

 With an average of 5.5 per cent oxygen, the minimum value 

 was 1 .0 per cent, and the maximum 9 . 5 per cent. Although most 

 of the values were very much nearer the mean than these, it is 

 essential that a considerable number of individual analyses be 

 made to determine the true mean for any given condition. 



Factors influencing amount 



Three main factors operate to determine the amounts of CO, 

 and oxygen in the intercellular spaces at any given temperature. 

 These are (1) the rate of oxidation, or the rate at which oxygen is 

 taken up from and C0 2 given off into the intercellular spaces; 

 (2) the permeability of the skin or epidermal covering to C0 2 and 

 oxygen; and (3) the difference in pressure of C0 2 and oxygen 

 within and without the fruit, which determines the rate of gaseous 

 exchange when the permeability factor is constant. The effect 

 on each of these factors of varying the temperature will explain 

 the variation occurring in the internal atmosphere of the tissues 

 studied at the different temperatures. 



Effect of temperature on oxidation processes. — -Gore (6) 

 has found that the rate of respiration for a large number of fruits, 

 as measured by the quantity of C0 2 given off, increased, on an 

 average, 2.38 times for a io° rise in temperature. Enzymatic 

 processes in general, within the range of temperatures here studied, 

 show an increase of from two to three times for each io° rise. 

 It is thus apparent that the oxidative processes will be speeded 

 up very markedly by temperature increases. 



Effect of temperature on permeability. — Denny (3), in a 

 study of the permeability of a number of plant membranes, has 



