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different en-Tironments and from different parts of the world. Although 

 a summary of these investigations has been brought to publication^'^ >", 

 many observations upon which the summary was based have not been pre- 

 sented heretofore. 



These studies of the chloroplast pigments from various plants were 

 also pursued with the object of ascertaining the variability of the 

 photosynthetic apparatus o In this way, it was hoped to gain clues to 

 those pigments that play critical roles in the photosynthetic process 

 itself. 



Lability of the Chloroplast Pigments 



An unanticipated outcome of these chromatographic studies was the 

 observation that the natural pigments themselves are remarkably labile 

 substances^ . They undergo several kinds of alteration yielding other i 

 colored substances. The nature of these reactions, their extent, and 

 the yield of the secondary products vary with the plant material, with 

 its treatment, and with the conditions to which the extracts are exposed^ 

 Special care must be exercised in the extraction and separation of the 

 pigments in order to prevent contamination of the natural pigments with 

 these alteration products. 



The principal secondary pigments that may contaminate the chloro- 

 plast pigments are described in part III, They include isomerization, 

 oxidation and acid alteration products of the chlorophylls and carote- | 

 noids5-6. 



Pre sentation of Observations 



As the chloroplast pigments were separated by chromatography and 

 as the chromatographic patterns serve for the description and definition 



