MISCELLANEOUS 



405 



oxygen absorption is taken after 92 hours in the various concentrations. 

 At longer periods of exposure (as long as 8 days) the acceleration of oxygen 

 uptake in 60 per cent CO2 exceeded 400 per cent instead of 230 per cent, 

 as at the end of the 92-hour period, and at shorter periods of exposure the 

 acceleration falls off as the period of exposure is shortened. In the concen- 

 tration of CO2, 10 to 40 per cent, the acceleration of oxygen absorption is 

 relatively slight, but rises rapidly as the concentration rises from 40 to 60 

 per cent. In the carrot the rate of oxygen absorption is plotted after 62 

 hours of exposure. At this time the rate had reached its maximum, and 

 there is relatively slight acceleration even at the highest concentration of 

 CO2. For asparagus shoots, the respiration rate was plotted after 20 hours 

 of exposure, at which time the rate had reached its minimum. All concen- 

 trations of CO2 above 10 per cent give significant fall in the oxygen absorp- 

 tion rate; but even the highest concentrations used give less than 40 per 

 cent fall. 



+ 120 



a. 

 O 



<-\ 



+ 



z 



uj UJ 

 u) O 



< X 



a. 

 u 



z 



Cl 



D + 80 



+ 40 



Z LlJ 

 IjJ uJ 



a Q 



-40 



20 30 40 50 



PER CENT CARBON DIOXIDE 



Figure 160. Effect of carbon 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 CO2 at 25° C (77° F). Periods of exposure: potato, 

 73; onion, 90; tulip, 68; and strawberry, 22 hours. 



Fig. 160 shows the effect of different concentrations of CO 2 with 20 per 

 cent O2 upon the oxygen uptake of dormant potato tubers, onion bulbs, 

 tulip corms, and strawberry fruits after the following periods of exposures: 

 73, 90, 68, and 22 hours respectively. In the dormant potatoes and onions, 

 concentrations of 20 per cent or lower have little effect on the oxygen 

 absorption rate. At higher concentrations the rate rises as the concentra- 

 tion of CO2 rises. In tulip corms the lower concentrations of CO2 depress 

 oxygen absorption slightly and higher concentrations accelerate it slightly. 

 The oxygen absorption of strawberries is depressed slightly, if at all sig- 



