406 



GROWTH OF PLANTS 



nificantly, at low concentrations and relatively slightly but significantly at 

 higher concentrations. 



Even in the potato tubers, in which high concentrations of CO 2 raise the 

 respiration rate enormously if the exposure period is sufficiently long, there 

 is a depression in oxygen absorption during the first 20 to 24 hours of 

 exposure. Fig. 161 shows this situation when 56 per cent CO2 is used. 



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48 



Figure 161. Influence of CO2 on the rate of oxygen uptake by dormant Irish Cobbler 

 potatoes at 25° C (77° F). 



Efifect of carbon dioxide in the air on the ascorbic acid (vitamin C) con- 

 tent of fruits and vegetables. Carbon dioxide in the surrounding air 

 induces a great fall in ascorbic acid in some fruits and vegetables. Fig. 162 

 shows the effect of various percentages of CO 2 in the atmosphere at 22° C 

 (72° F) for 24 hours on the ascorbic acid content of asparagus sprouts. ^^ 

 The loss of ascorbic acid rises as the concentration of CO 2 rises until in 

 60 per cent CO2 about one-half the ascorbic acid is destroyed. It will also 

 be noted that the pH of the tissue rises from about 6.2 to about 7.1 pH as 

 the CO 2 concentration rises from to 60 per cent. There probably is a 

 causal relation between rise in pH and fall in ascorbic acid, since the latter 

 is protected by acids and is readily oxidized in basic solutions. Upon 



