Compounds in Chloroplasts oj Green Cells of Plants. 561 



pathologically chlorotic leaves. So that iron is as indispensable to the green 

 leaf as it is to the red blood-corpuscle. 



The remarkable thing, in view of this failure to develop chlorophyll in 

 absence of iron, is that chlorophyll itself is shown by all the more recent 

 researchers to be quite free from iron.* Chlorosis and its cure by iron 

 salts has accordingly remained a puzzle to plant physiologists ever since the 

 time of the discovery of Gris.f The experiments to be recorded below 

 furnish, for the first time, a rational explanation of chlorosis and its cure. 

 The iron salts are necessary for the formation of the colourless portion of 

 the chloroplast, for when all the chlorophyll and other fatty bodies and 

 pigments are removed from the chloroplast by extraction with alcohol, 

 and the colourless chloroplastic residue is treated with the micro-chemical 

 tests for inorganic iron, a positive reaction in unmistakable degree is iisually 

 given by the colourless residue of the chloroplast. 



This inorganic iron in presence of sunlight must give rise to photo- 

 synthesis and production of formaldehyde which is then carried on into 

 sugar and starches by other constituents of the chloroplast, and it is 

 probably here, somewhere in the later processes, that the chlorophyll finds 

 its function. The chlorophyll itself, as shown by the facts of chlorosis, its 

 removal by administration of iron, and the presence of iron salts in the 

 colourless part of the chloroplast, is a product of synthesis from colourless 

 substances or from the light-yellow pigment. For the production of the 

 chlorophyll under normal conditions, both the presence of iron and the 

 energy of sunlight are essential. 



The reason for the earlier erroneous view that the chlorophyll molecule 

 contained iron was that a certain fraction of the iron compounds contained 

 in the green leaf becomes extracted by the alcohol used in the first extrac- 

 tion of the leaf, \ so that all crude chlorophyll extracts contain iron. This, 

 however, disappears on treating the alcoholic extract with benzol, and the 

 product of purer chlorophyll separating from the benzol fraction is iron- 

 free. At the same time its spectrum and other physical properties prove it 

 to be unaltered chlorophyll. 



Other facts which show the importance of iron compounds in the green 

 leaf are that leaves which are not deciduous annually, such as pine needles, 

 contain more iron in their later years, and also in leaves of annual growth 



* See Molisch, loc. cit., and R. Willstatter u. A. Stoll, " Untersuchungen iiber Chloro- 

 phyll,' Berlin, J. Springer (1913). 



t See Czapek, ' Biochemie der Pflanzen.' 



\ According to early observations of Boussingault ( Agronomie,' vol. 5, p. 128) from 

 one-quarter to one-third of the iron is removed by the alcohol. 



