206 HISTORY OF BOTANY 



he could find no coincidence between the maximum of 

 carbon dioxide decomposition and that of luminosity. 



In 1872 Kraus published his well-known method of 

 separating crude leaf green into cyanophyll and xantho- 

 phyll by shaking up an alcoholic solution of leaf green 

 with an equal volume of benzin, but many of his critics 

 insisted that chlorophyll was a single pigment, and 

 that cyanophyll and xanthophyll were decomposition 

 products. 



Quite a number of papers appeared in 1873 and 1874 

 which aimed at confirming the fundamental thesis laid 

 down by Sachs and at filling up the gaps in the story, 

 while several further attempts were made to determine 

 the exact composition of chlorophyll and to isolate it 

 in a pure condition. In 1875 Timiriazeff attacked the 

 views of Draper and Pfeffer more especially, and advanced 

 new evidence in support of his previous conclusion that 

 the really effective rays in photosynthesis were those 

 between the lines B and C of the spectrum. He employed 

 the eudiometric method of measurement of oxygen 

 exhalation, discarding Dutrochet's and Sachs's gas bubble 

 method as unreliable. 



Among the many publications of the next five years 

 I need only mention one by the French chemist Gautier, 

 in which he showed that chlorophyll contains no iron, 

 and that chemically the green colouring matter was 

 allied to bilirubin, one of the bile pigments. In 1875 

 Hoppe-Seyler attempted a new analysis and confirmed 

 the absence of iron but demonstrated the presence of 

 magnesium. 



The year 1879 saw the publication of the first of a 

 long series of monographs by Pringsheim, in which he 

 tried to establish an entirely new theory as to the function 

 of chlorophyll. Although Pringsheim's hypothesis has 

 long since been discarded, the papers themselves and the 

 criticisms to which they gave rise occupy so much of the 

 literature of the period that, from the historical point 



