Carbon Assimilation. 
287 
The alcohol solution of carotin or xanthophyll has a spectrum 
with one hand 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 ( Urtica 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. 
