OF THE GKEEN CELLS OF PLANTS 57 



as the reserve store of iron always contained in the seed embryo and 

 cotyledons has been exhausted in the primordial leaves, only 

 chlorotic pale yellow leaves are formed. These pale yellow leaves 

 rapidly turn green if minute quantities of an iron salt are added to 

 the culture fluid, or even if the surface of the leaf be painted over 

 with a dilute solution of an iron salt, as had been previously shown 

 by Gris to be the case with 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 chloro- 

 phyll in absence of iron, is that chlorophyll itself is shown by all the 

 more recent researchers to be quite free from iron. 1 Chlorosis and 

 its cure by iron salts has accordingly remained a puzzle to plant 

 physiologists ever since the time of the discovery of Gris. 2 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 chloroplasts, 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 un- 

 mistakable degree is usually 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 



1 See Molisch, loc. tit., and R. Willstatter u. A. Stoll, " Untersuchungen 

 iiber Chlorophyll," Berlin, J. Springer (1913). 



2 See Czapek, ' Biockeiuie der Pflanzen." 



