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SCIENCE PROGRESS 



obtaining with a medium acid content. Many conjectures 

 have been made as to the fate of the acid which disappears, 

 but no definite facts are known. It is not unlikely that it 

 also forms the material for respiration. 



The disintegration of carbohydrates and acids involves the 

 production of carbon dioxide, and it is therefore interesting 

 to measure the output of carbon dioxide and correlate it with 

 the state of ripening. It has indeed been suggested 1 that the 

 amount of carbon dioxide evolved by unit weight in unit time 

 may be taken as a measure of ripening velocity. We give 

 below in table form a few examples from Gore of this value, 

 which we propose to call the " respiration number." 2 



Gore's experiments were carried out at various tempera- 

 tures and he found that the relation between respiration and 

 temperature can be characterised by the equation 



log y = log y Q + at 



where y is the respiration at a temperature t°C, 



JVo )y ) f >t tt ° C., 



and a is a constant, which does not vary much for different 

 fruits, its average value being 0-0376. In the table the respira- 

 tion numbers are all reduced to o°C. 



It will be seen from the table that the values vary a good 

 deal, the highest value being found for soft fruits with the 

 exception of red currants and grapes, average values for stone 

 fruit, smaller values for apples and pears, and the smallest for 

 citrous fruits. Summer apples respire more rapidly than winter 



1 Gore, "Studies on Fruit Respiration, 55 U.S. Department of Agriculture, 

 Bureau of Chemistry, Bull. 142, 191 1. 



s This is analogous to the term "assimilation number" introduced by Willstatter 

 and Stoll to represent the number of grams of carbon dioxide assimilated in one 

 hour by 1 mg. of chlorophyll. See Willstatter and Stoll, Untersuchungen uber 

 die Assimilation der Koklensaure, Berlin, 1918. Of course the analogy can only 

 be approximate until one can determine the exact weight of respiratory material, 



