MISCELLANEOUS 403 



vegetables, and meats in cold storage. Sclerotinia, as do many fungi, grows 

 best in a slightly acid medium and a shift of the culture medium in the 

 alkaline direction is more unfavorable than a similar shift toward the acid. 

 On the basis of his studies, Thornton suggests that CO 2 in the atmosphere 

 inhibits or ''stales" the growth of fungi by rendering the protoplasm more 

 alkaline rather than by acidulating the culture medium. 



Thornton's work ^- on the effect of various concentrations of CO2 in the 

 atmosphere on the pH and the change in color of various flowers is most 

 interesting, for the flowers studied bore anthocyanins that indicate the 

 more alkaline cell sap in the presence of CO 2 by a shift of color from red- 

 dish toward the blue. The flowers were placed in 20, 30 to 35, 50 to 60, and 

 80 per cent CO2 with 20 per cent O2, and the following flow^ers were used: 

 rose (Templar and Briarcliff), Verbena phlogiflora, pink peony, and four 

 varieties of Japanese iris (violet to purple). The change in pH as shown 

 by the change in color of the flower was checked by extracting and deter- 

 mining the pH of the juice electrometrically. The shift toward the alka- 

 line amounts in some cases to 0.8 of a pH. While the exposures were 

 for 18 hours at 22° C (72° F) the change in color, as would be expected in 

 these thin organs, occurred in much shorter time. When the flowers are 

 removed from the CO 2 the petals return to their original color within a 

 few hours, if they are not injured by too high concentration of CO2 or too 

 long an exposure to it. Very old and injured petals did not show the shift 

 toward alkalinity. The change is brought about by metabolic activity of 

 living protoplasm and probably involves both synthetic and catabohc 

 changes. 



The four irises selected for the study proved especially favorable for 

 sho^ving the change in flower color. The pH of the cell sap of the flower 

 segments in these in air was 6.46, 6.47, 6.34, and 6.41 respectively, and in 

 50 to 60 per cent CO2 it shifted to 7.20, 7.32, 6.96, and 7.18 respectively. 

 Except for one, the shift was from acid to alkaline and that one became 

 practically neutral. Furthermore, the anthocyanins in the flower segments 

 shifted from violet to blue very near the neutral point as the sap became 

 more alkaline. Violet flowers in air soon became blue flowers in 50 to 60 

 per cent CO2. Fig. 158 shows the colors of the flowers of one variety in air, 

 in 30 to 35 per cent CO2, and in 50 to 60 per cent CO2. In the flowers 

 studied other than iris, the cell sap in air showed a pH range from 5.17 to 

 5.54; consequently the shift in pH even in 80 per cent CO 2 was not sufficient 

 to reach the neutral point. In fact, the greatest shift in these was in the 

 petals of Briarcliff rose which was from 5.21 to 5.88 pH, or about 0.7 pH. 



Effect of carbon dioxide on the respiration rate of plant ^tissue. Since 

 CO 2 is an end product of respiration, perhaps it is sometimes assumed that 

 its accumulation about the plant in considerable concentration reduces 

 the respiration rate. Since respiration is a complex process involving 

 many enzymes and chemical reactions, such an assumption is hardly 

 justified. Thornton's studies ^^' ^^ show that with some plant organs under 



