1 8 Carbon Assimilation. 



The alcohol solution of carotin or xanthophyll has a spectrum 

 with one band in the blue and another in the indigo blue and the 

 end absorption commences in the violet. The bands in the case of 

 xanthophyll are displaced a little towards the violet as compared 

 with carotin. 



In carbon-disulphide solutions the difference between the two 

 spectra is greater, and the absorption bands are displaced towards 

 the red end as compared with those in alcoholic solution. 



D. The Extraction and Preparation of the Pure Pigments 

 FROM THE Leaf. 



(1) The Choice of a species. In obtaining the pigments of the 

 leaf in the free state it is obvious that the first question to arise is 

 the choice of material from which the pigment should be extracted. 

 This question immediately resolves itself into two : firstly, the 

 choice of a species on which to work, and secondly, the preparation 

 of the leaves for treatment with the solvent. 



In regard to the choice of a species, Willstatter divides plants 

 into two groups, (i) Those rich in the enzyme chlorophyllase, 

 which on extraction of the pigment give the substance known as 

 "crystalline chlorophyll" (chlorophyllides). In this group are 

 hogweed (Heracleum sphondylium), hempnettle (Galeopsis Tetrahit) 

 and the hedge woundwort {Stachys sylvatica). (ii) Those poor in 

 chlorophyllase, which on extraction of the pigment give true 

 chlorophyll. Of the plants in this group Willstatter recommends 

 for use the nettle {Urlica sp.) which is very abundant, is rich in 

 chlorophyll, and poor in enzymes. Nettles are easily dried and 

 when dried they keep well. They have the disadvantage that in 

 the process of extraction the chlorophyll is easily altered, but this 

 disadvantage can be obviated by quick preparation. 



It is interesting, as Willstatter points out, that as long ago as 

 1852, G. G. Stokes proposed the use of nettles as a source of 

 chlorophyll. 



(2) The Preparation of the Leaves. The earlier preparations of 

 chlorophyll were nearly all made by boiling fresh leaves in alcohol, 

 and for this purpose, on account of its abundance, grass was very 

 commonly used. Sometimes the fresh leaves were first boiled with 

 water, after which the pigment could be extracted with warm 

 alcohol. Hoppe-Seyler first treated the leaves with ether in order 

 to extract the waxes, before extracting the pigment with boiling 

 alcohol. 



