ASSIMILATION OF CARBON 9 



of the manner in which the magnesium atom is probably related to the other 

 components of the molecule may be obtained from the following structural for- 

 mula for etiophyllin, to which this fundamental acid is apparently closely 



related. 



CH = CH 



CH 3 -C— CH C— C 



II > N \ K I 



C2H5— C— C C— CH 



> c 4 Lc < 



C2H5— C = C \ / C = C— C2H5 



\n— Mg— Nc 



CH3— C = C C = C— CH 3 



CH 3 CH3 



When the phytyl group of chlorophyll a is replaced by the ethyl group 

 C 2 H 5 ), a substance is obtained (CsyHssOe^Mg) which Willstatter called 

 ethyl chlorophyllide. This forms beautiful crystals, which were earlier mistaken 

 for pure chlorophyll. Chlorophyll b reacts in a similar way. According to the 

 method of Monteverde, 1 these crystals may be obtained by treatment of tritu- 

 rated leaves with 95 per cent, ethyl alcohol; after an hour the extract is filtered 

 and the alcohol is removed by evaporation, either in air or in hydrogen. The 

 crystals are separated from impurities and from the yellow pigments by means 

 of distilled water and benzine. In the pure condition they form a dark green, 

 almost black powder, with a bluish metallic luster. Their alcoholic solution is 

 green, with a beautiful red fluorescence. Although the solution is unstable in 

 light, the crystals can endure intense light for a long time without change. The 

 following plants serve especially well as sources of ethyl chlorophyllide in the 

 crystalline condition: Dianthus barbatus, Lathyrus odoratus, Galeopsis versicolor, 

 G. tetrahit, Acacia lophantha, and Dahlia variabilis. Amorphous chlorophyll 

 may be obtained from many other plants. Willstatter and Benz 2 obtained 

 over 2 g. of ethyl chlorophyllide from 1 kg. of dry leaves. 



The absorption spectrum of chlorophyll deserves special attention. Light 

 of certain ranges of wave-length is more or less completely absorbed by the 

 solution, so that dark bands appear in the spectrum. The absorption spectrum 

 of every colored solution changes with its concentration. On this account the 

 spectrum of chlorophyll solution must be determined either throughout a range 

 of concentrations or by using layers of various thicknesses. Six absorption 

 bands are found in the spectrum (Fig. 4) of ethyl chlorophyllide; arranged ac- 



1 Monteverde, N. A., Ueber das Protochlorophyll. Acta Horti Petropolitani 13 : 190-217. 1804. 

 Borodin had obtained crystals from chlorophyll before they were described by Monteverde. See: Borodin, 

 J., Ueber Chlorophyllkrystalle. Bot. Zeitg. 40: 608-610, 622-626. 1882. 



2 Willstatter and Benz, 1 098. (See note 1 , p. 8. ] 



