MISCELLANEOUS 



Table 45. Effect of an Atmosphere Containing 50 to 70 per cent CO2 



and 20 per cent O2 on the pH of Living Tissue of Various Plants. 



Determinations Made on E.xtracted Juice by Means of Glass Electrode 



and Quinhydrone Apparatus. Temperature, 25° C (77° F) 



401 



was slight to moderate. The shift was rapid in leafy tissues where large 

 surface per volume exists, as in the tomato and tobacco plants, and slow 

 where the tissue was massive as in fruits, tubers, bulbs, and fleshy roots. 



Asparagus shoots showed significant changes in pH with 15 minutes of 

 exposure and potato tubers only after 12 or more hours. When tissues 

 were placed back in air they gradually recovered the original pH. This 

 requires 20 to 24 hours for asparagus shoots and 48 to 72 hours for potato 

 tubers. Cut pieces as well as the whole tubers of potatoes show the change. 

 In untreated tubers the tissue near the surface is more acid than the deeper 

 tissue, but CO 2 treatment reverses this. The pH of potato tubers is lower 

 when they are stored at low temperatures than at high; but CO2 increases 

 the pH even at 2° C (36° F), although more slowly than at 25° C (77° F). 

 The increased alkalinity caused by high concentrations of CO2 seems to 

 depend upon aerobic respiration, for in absence of 2 in the atmosphere 

 high concentrations of CO 2 cause potato tubers to become more acid. 



The researches on the effect of CO 2 on the pH of the hyphae of Sclero- 

 tinia frucUcola in culture *^ are of especial interest because they involve a 

 a ^^^de range of concentration of C02-and of temperature, and the pH shift 

 is large. The pH of the hyphae and culture medium was determined colori- 

 metrically by indicators and by the quinhydrone apparatus; in addition, 

 the glass electrode was used for the hyphae. Table 46 shows the shift in 

 the pH after 24 hours in four different concentrations of CO2 and at six 

 different temperatures. The total shift in pH is induced by four hours' 

 treatment, and no additional change occurs even up to 120 hours' exposure. 

 It will be noted here that the shift in pH occurred at all temperatures, 

 being somewhat higher at 2° and 5° C (36° and 41° F) than at higher tem- 

 peratures. It will also be noted that even 10 per cent CO 2 induces a marked 



