Variations in Quantity of Leaf Pigments. 39 



the colorimetric and spectroscopic methods of estimation hitherto 

 employed.^ 



Wilistatter himself has so far used only colorimetric methods, 

 for it is of no value to make measurements of a high degree of 

 accuracy before possible errors in the extraction and separation of 

 the pigments have been eliminated. When this has been done 

 Wilistatter suggests that quantitative spectroscopic analysis may 

 prove very useful as a further refinement in the quantitative 

 estimation of the pigments. 



We shall give in some detail Willstatter's latest methods for 

 the quantitative estimation of the pigments, more particularly as 

 Wilistatter in his latest publications (1915 b, 1915 c) applies 

 them to plant-physiological work. 



It is scarcely necessary to emphasise the extreme importance 

 of obtaining reliable methods for the determination of the 

 quantities of pigments in leaves. While Willstatter's earlier work 

 in this respect, which is published in his book (1913), was mainly 

 done in order to test the validity of his methods, yet he made also 

 some estimations to determine whether there was any regularity in 

 the variations in the quantity of the pigments in leaves, and these 

 estimations yielded figures very suggestive with regard to the 

 physiological function of the pigments. Now Wilistatter has 

 definitely taken up the plant physiological aspect of this question, 

 but it must not be forgotten that his work in this regard has so far 

 been very limited and undertaken from a purely chemical point of 

 view. It remains for the plant physiologist and ecologist to take 

 up the methods and apply them in their various departments of 

 research. 



Of course the technique of these methods is not to be acquired 

 without some trouble and practice, but their employment appears 

 at present the only way to reliable results. 



It is not our intention to give an historical survey of the 

 considerations which led Wilistatter to the methods he ultimately 

 adopted. They were developed for the purpose of comparing the 

 pigment-content of various extracts and preparations. Thus, if for 



' For instance, in reference to a recent paper by Jacobson and Mai'cn- 

 lewslii (1912) where the authors claim to have shown that climatic conditions 

 play an important part in regard to the production of one or other of the 

 chlorophyll components, Wilistatter points out that some of the errors com- 

 mitted by these workers were (1) only a fraction of the chlorophyll present 

 was extracted, (2) an unknown portion of the extracted pigment was precipi- 

 tated as phacophytin, and (3) only a portion of the phicophytin was isolated. 



