46 MINERAL NUTRIENT MATERIALS. 



ivon, the weight of the crop being about double that obtained in 

 cultures without iron. Presuming the experiments to have been 

 properly conducted, this result would justify the assumption that 

 iron, though very beneficial to the growth of the fungus in 

 question, is not indispensable. Raulin, however, suspected that 

 his " iron-free " cultures did not desei-ve their name, but con- 

 tained a small proportion of this metal as an insepai-able impurity 

 in the other salts. On these grounds, thoiTgh without proof, 

 Raulin concluded that iron is indispensable for the development 

 of Aspergillus niger. The contrary opinion, viz. that iron is 

 non-essential to fungi, was expressed by CuGixi (I.) in connection 

 with a pileated fungus, and by A. Schulz (I.) for Mycoderma 

 cerevisice ; though, as neither of them worked with solutions that 

 could be guaranteed free from ii-on, the question still remained 

 undecided. Hans Molisch (I. and II.) attempted to settle it, 

 without, however, succeeding in producing a perfectly iron-free 

 culture. Nevertheless, his results tend to prove the indispen- 

 sable character of the element in question, inasmuch as, in cultures 

 as free as possible from iron, the spores of Aspergillus niger did 

 not develop beyond the formation of a sickly mycelium, whereas 

 the specimens treated with an addition of iron not only exhibited 

 luxuriant growth, but also produced an abundance of spores. 

 Similar results were obtained with sowings of pressed yeast cells, 

 spores of Mucor racemosus, and a species of Penicillium. Bearing 

 in mind the observation (communicated by Molisch) that a 

 ferruginous ash is furnished even by cultures grown in a medium 

 from which iron has been, as far as possible, eliminated, and 

 therefore that even imponderable amounts of iron are greedily 

 absorbed, one is constrained to share the conclusion formed by 

 Molisch, that iron is very probably indispensable to the develop- 

 ment of fungi. The objection urged by C. Wehmer is based on 

 obseiwations that cannot be regarded as perfectly reliable. The 

 hypothesis was raised by H. Molisch (I.), and shortly after- 

 Avards by A. B. Macallum (II.), that iron occurs, in plants 

 generally and in fungi particularly, in the form of organic com- 

 pounds, and is therefore undetectible by the ordinary reactions. 

 Macallum (I.) then explained that the chromatin in the nuclear 

 structure (§ 252) of the cell is the chief seat of these organic 

 compounds of iron. The instances cited in suppoi't of this view, 

 however, have been strongly criticised, since they were based on 

 experimental methods the unreliability of which has been 

 demonstrated by Arthur ]Meyer, Carl jNIueller (L), and G. 

 GiLSON (I.), and also partly admitted by Molisch (III.) himself. 

 Nevertheless, as may be concluded from later observations, the 

 assumption itself seems appropriate. The first of these observa- 

 tions was made in 1877 '^J Lubavin, who detected the occurrence 

 of iron in the molecule of the paranuclein prepared from milk 

 casein. Further reports in this connection were made by A. 



