io8 



METABOLISM 



It is characterized by the presence of six absorption bands, three of which 

 are in the more refrangible (beyond F), the other three in the less refrangible 

 part. The bands occurring on the other side of F appear distinct only when 

 weak solutions are used ; in strong solutions they merge into one. Of the 

 three others, the first band (A = 670-635 /A/A) is by far the most intense ; the 

 second (A = 622-597 /A/A) and third (A = 587-565 /A/A) are much feebler. The figure 

 further shows, just in front of line E, a band which belongs, not to chlorophyll 

 itself, but to a decomposition product of it. A solitary chloroplast or a leaf 

 presents an absorption-spectrum in all respects similar to that given by the 

 solution, save that the bands as a whole are displaced somewhat nearer to the 

 red end, whence we may conclude that the colouring matter in the chloroplasts 

 is dissolved in a dense medium or occurs in a combined form. 



The crude chlorophyll we have hitherto been studying is, however, by no 

 means a simple body. As KRAUS (1872) has shown, it is possible, by shaking 



e 



ff 



9 \ 



fffO 



a \ to ,20 



so '.40 sot oo 10 so \ sa tot 



I II I ! I I , ! I I I 



i IB i SO SO \40 J0\ 60 10 



I I 



III 



Fig. 24. Absorption-spectrnm of chlorophyll (after KRAUS, 1872). /, alcoholic extract of the green leaf (crude 

 chlorophyll) ; //, spectrum of the blue-green benzene extract ; ///, spectrum of the yellow pigment. (From 

 DETMER'S Smaller Practical Physiology.) 



up an alcoholic solution with benzene, to obtain a blue-green dye more soluble 

 in the benzene, and a yellow dye which remains dissolved in the alcohol. The 

 spectra of these dyes is shown in Fig. 24, II and ///. Since the yellow dye has 

 nothing to do with carbon-dioxide assimilation, we may dismiss it from our 

 consideration in a sentence. It consists not of a simple compound but of a mix- 

 ture of at least three bodies : 



1. Chrysophyll, an undetermined hydrocarbon with formula C 26 H 38 , which 

 can be crystallized and is closely related to, if not identical with, carotin, a sub- 

 stance widely distributed in the plant world. Its spectrum shows three absorp- 

 tion bands beyond F. 



2. A substance which exhibits a spectrum with four absorption bands in 

 the more refrangible part, which are, however, not identical with those of 

 chrysophyll (xanthophyll, according to SCHUNK). 



3. Another substance, which gives no absorption bands but produces entire 

 obliteration of the violet and ultra-violet rays. 



The colouring matter dissolved in the benzene is also by no means a simple 

 body ; it consists, in addition to true ' chlorophyll ', of an admixture of a sub- 

 stance known as ' allochlorophyll ', though in very small quantity. Great 



