The Pigments of the Leaf. i i 



In the following sections of this chapter we propose to deal 

 more in detail with the chemistry of the pigments, their method 

 of extraction and variations in their amounts. It must, of course, 

 be understood that anyone wishing to ohtain first-hand knowledge 

 of these aspects of the subject must consult Willstatter's book (1913) 

 or his original papers referred to therein.' Most of the information 

 given in the succeeding sections of this chapter is due to Willstatter 

 and his co-workers. It is impossible to offer any criticism of the 

 methods or the results of Willstatter, and in many cases in the 

 following we have simply had to quote him without comment. 



In view of the information given by Willstatter's researches it 

 becomes unnecessary and would only be confusing, to enter into 

 any discussion of the different results obtained by other continental 

 investigators of this subject such as Hoppe-Seyler (1879, 1880, 1881), 

 Gautier (1879) and Stoklasa (1907, 1909, 1913). It is sufficient to 

 indicate that their results now appear due to their imperfect 

 methods of extraction. 



The difficulties of isolating chlorophyll, partly because it 

 changes so easily to other substances, and is so soluble in many 

 solvents, has had the result of producing a very voluminous 

 literature, but not even the most elementary questions had been 

 solved before Willstatter's researches. Thus it was not known 

 whether there was one chlorophyll substance or more than one 

 and as recently as 1906, Etard claimed to have found in one plant 

 a whole series of different chlorophyll pigments, and an unlimited 

 number of chlorophylls from different plants. Also the elementary 

 questions of analysis had not been solved. It was not even known 

 which elements were contained in the chlorophyll molecule. 



' How little notice has been taken of Willstatter's work by plant physiolo- 

 gists can be made clear by reference to recent work involving the use of 

 extracted chlorophyll. It is perhaps understandable that Wager in a paper 

 published in 1914 should be unaware of Willstatter's results, for not much 

 more than half a year had elapsed since the publication of Willstiltter's book ; 

 yet even so, accounts of many of the researches summarised in that book have 

 been easily accessible in original papers for some years. Again, in the paper . 

 by Ewart (1915) already referred to, in which Wager's work is criticised, there 

 is no ev>dence of close acquaintance with Willstatter's work, for the author 

 gives as the source of his information, the account of Willstiltter's researches 

 given by Haas and Hill (1913). This, however, may be explained by the fact 

 that Ewart is working in Australia and some time is required for German 

 publications to reach so far. But it is difficult to understand how Chodat, 

 working in a country so near Germany as Switzerland, in a paper (1915) 

 published three months after Ewart's, should make no reference to 

 Willstatter's, but should recommend the methods of chlorophyll extraction 

 worked out by Hoppe-Seyler which date back to the years 1879 to 1881. 



