198 Alfred J. Eivart .- 



carotin residue combines with the glaiicophyllin, converting it intO' 

 the tricarboxylic chlorophyll. This process involves an absorption 

 of oxygen. If carbon dioxide is present, it interacts "with the 

 chlorophyll, probably undergoing additive combination. If it 

 tlieu separated formaldehyde and phytyl, it would liberate a 

 large amount of oxygen. The phytyl would then recombine with 

 the glaucophyllin, reforming the chorophyll molecule. If the 

 supply of carbon dioxide was abundant in proportion to the inten- 

 sity of illumination, the decomposition and recombination would 

 balance and an evolution of oxygen Avould be possible without any 

 actual accumulation of chlorophyll taking place. In 1896 I was 

 able to confirm on a variety of plants the statements of Draper and 

 of Englemann that etiolated chloroplastids can evolve oxygen in 

 light,*!- and showed that this took place before any actual chloro- 

 phyll was developed. The rule was not a universal one, however, 

 and particularly in the case of maize, which has a high temperature 

 minimum for the formation of chlorophyll, no evolution of oxygen 

 could be detected from etiolated leaves so long as they were free 

 from chlorophyll. It was also shown that sealed preparation of 

 etiolated leaves of Elodea with Bacteria, owing to the presence of 

 an excess of carbon dioxide did not turn green in light, although 

 they produced the small amount of oxygen necessary to support 

 protoplasmic streaming. 



The presence of from 2% to 5% of carbon dioxide in the sur- 

 rounding air distinctly retards the turning green of etiolated grass 

 seedlings as compared with those in ordinary air, 2 but if the in- 

 tensity of the illumination is approximately quadrupled, the re- 

 tarding action of the carbon dioxide is less pronounced or even 

 ceases to be perceptible. Kohl^ ten years later without referring to 

 the previous work reconfirmed the statement that etiolated plants 

 may evolve oxygen in light. He showed that carotin was the chief 

 pigment in etiolated plants, and held that it was responsible for the 

 assimilation of carbon dioxide in the absence of chlorophyll. It 

 is, however, more probable that the evolution of oxygen takes place 

 as outlined above, and that carotin is not by itself capable of caus- 

 ing the assimilation of carbon dioxide. Actual observation shows 

 that it does not appear to comljine with carbon dioxide, and that 

 it combines more energetically and rapidly with oxygen than either 

 chlorophyll or xanthophyll does. Tlie formaldehyde produced 



1 See Journal of Liiinean Society, vol. xxxi., 1896, p. 554. 



2 See also Bohni, Sitzungsb. d. Wien. Akad,, 1878, p. 14. 



3 F. G. Kohl, Ber. d. D. Bot. Ges., 19(»6. vol. xxiv., p. 222. 



