404 



GROWTH OF PLANTS 



certain conditions CO 2 in the atmosphere surrounding the organ increases 

 the oxygen absorption markedly, whereas with other organs it decreases 

 this phase of respiration under a wide range of concentrations and other 

 conditions, and finally that it does not affect measurably the rate of oxygen 

 uptake by still other organs. A careful examination of all of Thornton's 

 data ^^ indicates that plant organs with normally low respiration (potato 



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20 30 40 50 



PER CENT CARBON DIOXIDE 

 Figure 159. Effect of earbon dioxide upon the oxygen uptake by various tissues. 

 The controls are plotted at zero. The curves show percentage increases or decreases in 

 oxygen uptake by tissues treated with carbon dioxide at 25° C (77° F). Potatoes at 92, 

 carrots at 62, and asparagus at the 20-hour period of CO2 storage. 



tubers) have oxygen absorption increased by CO 2 and those normally high 

 (asparagus shoots) have the oxygen uptake decreased by CO2. Those 

 organs vAih. moderate respiratory rates are less or not at all affected. Even 

 old non-dormant potato tubers with a low respiration rate were increased 

 more in their oxygen absorption by CO 2 than freshly harvested tubers 

 with high normal respiration. 



Fig. 159 shows the effect of different concentrations of CO 2 with 20 per 

 cent O2 on the oxygen uptake rate of non-dormant potato tubers, carrot 

 roots, and asparagus shoots. In the non-dormant potatoes the rate of 



