ASSIMILATION OF CARBON 7 



Alcoholic solution of chlorohyll a is blue-green by transmitted light and 

 blood-red by reflected light; it is said to fluoresce blood-red. Alcoholic solu- 

 tion of chlorophyll b is yellow-green by transmitted light and fluoresces brown- 

 red. This phenomenon of fluorescence (seen also in a solution of the red dye 

 eosin, which fluoresces green) appears to be due to an alteration in the wave- 

 length of radiant energy, brought about by a peculiar action on the part of the 

 molecules in the solution. By this action the chlorophyll solution gives off 

 energy of long wave-lengths (red light) when it is illuminated by energy of 

 much shorter wave-lengths (green and blue light)/ 



Of the total green pigment, as obtained from leaves, about 72 per cent, is 

 chlorophyll a and the rest chlorophyll b. The proportions vary somewhat, but 

 the variation is not over 10 perc ent. Both form crystals. The two chloro- 

 phylls'' have the following formulas, as so far known: 



Chlorophyll a, C 55 H 72 6 N 4 Mg 

 Chlorophyll b, C 5 5H 7 o0 6 N 4 Mg 



It is seen that both contain magnesium, the content of this element being about 

 5.6 per cent., by weight. Iron is apparently necessary for the formation of 

 chlorophyll in plants, but it is not a part of the pigment. Iron does occur, 

 however, in the molecule of hemoglobin, which is somewhat closely related to 

 chlorophyll, chemically. An explanation 6 of this is to be found in the fact that 

 the actions of these two substances in the cell are directly opposed; for the 

 analytic action of hemoglobin, iron is essential, while magnesium seems to 

 take part in the synthetic processes effected by chlorophyll. 1 



1 Willstatter, Richard, Zur Kenntniss der Zusammensetzung des Chlorophylls. Liebig's Ann. Chem. u. 

 Pharm. 350: 48-82. 1906. Willstatter, Richard, and Benz, Max, Ueber krystallisirtes Chlorophyll. 

 Ibid. 358: 267-287. 1908. 



c This explanation is not given by Palladin. For a discussion of the various theories regard- 

 ing the color and fluorescence of plant pigments, see : Horowitz, B., Plant pigments. Biochem. 

 bull. 4: 161-172. 1915. — Ed. 



d Stokes had long ago suspected that chlorophyll is a mixture of two green pigments. In 

 this connection see: Stokes, G. G., On the supposed identity of biliverdin with chlorophyll, 

 with remarks on the constitution of chlorophyll. Proc. Roy. Soc. London 13 : 144-145. 1864. 

 Sorby, H. C, On comparative vegetable chromatology. Ibid. 21 : 442-483. 1873. 



On an interesting method for separating the yellow and green pigments by absorption in 

 paper or in a column of calcium carbonate, see: Tswett, M., Physikalisch-chemische Studien 

 liber das Chlorophyll. Die Adsorptionen. Ber. Deutsch. Bot. Ges. 24: 316-323- ia° 6 - 

 Idem, Adsorptionsanalyse und chromatographische Methode. Anwendung auf die Chemie 

 des Chlorophylls. Ibid. 24 : 384-393. 1906. Idem, Ueber die nachsten Saurederivate der 

 Chlorophylline. Ber. Deutsch. Chem. Ges. 41/: 1352-1354. 1908.— Ed. 



e It is difficult to understand this as an explanation. It must not be understood that 

 hemoglobin and chlorophyll are really very much alike; they differ very markedly, but give 

 some of the same decomposition products. It is true that both are related to the interchange, 

 between the organism and its surroundings, of carbon dioxide and oxygen, but the actions of 

 the two substances do not appear to be similar in detail. The author refers here to the fact 

 that they have similar component atomic groups, which may suggest that, in the phylogeny 

 of animals and plants, both groups of organisms may have developed from a common ancestral 

 form having a substance with the characters that are common to hemoglobin and chlorophyll. 

 This is as far as such a theory may go at present. But see below, page u, ct seq.—Ed. 



