CO IRON COMPOUNDS IN THE CHLOROPLASTS 



It is somewhat remarkable that the presence of iron in the 

 chloroplast should for so long have escaped discovery. The ex- 

 planation probably lies in the fact that little attention has been given 

 to the application to the green cell of the histo chemical tests for 

 iron since the discovery by Macallum of the more delicate haema- 

 toxylin iron test, as also to the delicacy of the chloroplasts to the 

 more drastic earlier method used by Molisch, and to these factors 

 may be added the difficulty with which some of the chemical reagents 

 for iron penetrate the green cell, and the presence in the chloroplast 

 itself of fatty and lipoidal substances which prevent the ingress of 

 the water-soluble stains. 



Macallum 1 in 1894, before his discovery of unmordaunted 

 haematoxylin as a reagent for iron, and using then ammonium 

 sulphide in glycerine as a reagent, states that bacteria gave no 

 evidence of an inorganic iron compound, but in the cyanophycea3 

 the chromophilous portions of the " central substance " contain 

 iron, and iron may be also demonstrated in the peripheral granules 

 containing the so-called cyanophycin. At this period, Macallum 

 was specially concerned in proving the presence of inorganic iron in 

 the chromatin of the nucleus and was not searching for iron in the 

 chloroplasts, so that the reference above to the presence of iron in 

 the cyanoplasts of the cyanophyceae is highly interesting to-day. 



Molisch (loc. cit.) used long immersion in saturated potassium 

 hydrate as a preliminary method for setting free masked iron (i.e., 

 organic iron) in available form for after- detection by potassium 

 f errocyanide and hydrochloric acid, and in the later testing used very 

 strong hydrochloric acid (10 to 20 per cent.). Such drastic proce- 

 dures are very dangerous, because the alkali breaks down the delicate 

 chloroplasts, and may also itself contain iron salts in traces; also, 

 in the second place, as pointed out by Quincke, 2 such strong acid 

 will fairly rapidly set iron free in inorganic or ionic form from the 

 potassium ferrocyanide reagent, and this ionic iron reacting with 

 the remainder of the reagent will give the Prussian blue colour. 

 Molisch found more iron in the epidermis and fibro- vascular bundles 

 of green leaves than in the green mesophyll, but, as he himself 

 admits, " the potassium hydrate so disorganises the nucleus and 

 chlorophyll-granules that one can conclude nothing as to the 

 distribution of iron in the cell." 



1 Boy. 8oc. Proc., vol. Ivii., p. 261 (1894). 



2 Arch.f. Exp. Path. u. Pharm., vol. xxxvii., p. 183 (1896). 



