402 



PLANT GROWTH 



Table 46. pH of the Hyphae of Sclerotinia frudicola Held at Various 

 Temperatures during Exposure to Various Concentrations of Carbon 



Dioxide for 24 Hours 



change, with 20 per cent considerably more effective. The pH rises slightly 

 as the concentration of CO 2 rises to 40 and finally to 60 per cent. Concen- 

 trations higher than 60 per cent give no additional rise in pH. The greatest 

 shift shown was 2 pH, which means 100-fold rise in the alkahnity and a 

 corresponding fall in acidity. 



While CO 2 m the surrounding air renders the living hyphae more alka- 

 line, it makes the culture medium and the dead hyphae more acid. These 

 changes are shown in Fig. 157. 



Thornton mentions that several workers have found 10 to 30 per cent 

 CO2 in the atmosphere effective in reducing fungus growth. Such concen- 

 trations of CO2 have also been found to suppress fungus growth on fruits, 



STERILE MEDIUM 



CULTURE MEDIUM AFTER GROWTH OF FUN GUS 



< ^ 



TREATED 



CONTROL 



DEAD TISSUE 



LIVING HYPHAE 



pH 



Figure 157. The effect of 60 per cent of CO2 on the pH of living and dead hyphae 

 of Sclerotinia fructicola and on the sterile and inoculated culture medium during 24 hours 

 of storage at 22° C (72° F). The pH of the Uving hypha and the culture medium at 

 the beginning of the treatment is shown by the vertical lines. The arrow indicating a 

 pH of 4.3 on the line of the inoculated culture medium represents the pH of the medmm 

 developed during 6 days' growth of the fungus. The arrow at pH 4.1 represents the 

 additional change brought about by the CO2 treatment. 



