366 The Physiology of Plants BOOK in 



and in the diffuse chromatin which slowly passes from the 

 nucleus into the cell. Macallum himself observed it in the 

 chromatin of the ovules, while McKenzie found it in the 

 same constituent of the spores of certain Fungi and Algae. 

 ' In the next year Petit found it combined with nuclein in the 

 tegmen and the embryo of the barley grain, and in 1893 

 in the rootlets protruded by the germinating grain . Bensley , 

 in the same year, obtained a reaction by it in the nuclei 

 of the cells of the ovary of Erythronium. 



Macallum noticed its occurrence in a few cases in the 

 cytoplasm, particularly in the cells of the aleurone layer 

 of the wheat grain, and in the spores and hyphae of certain 

 Fungi, in the nuclei of which it was present also. He 

 did not regard this distribution as indicating that the iron 

 of the chromatin is derived from the cytoplasm. 



Physiological observations on the function of iron have 

 led to little. Bracci found that its presence hastened the 

 ripening and increased the yield of oats and wheat. Molisch, 

 in 1892, observed a great effect produced by it on the growth 

 of fungi. In 1888 Gautier and Drouin found that ferric 

 oxide promotes the fixation of atmospheric nitrogen by 

 the soil bacteria. Pfeffer claimed that the chlorosis due to 

 its absence is not caused by its being directly concerned 

 in the formation of chlorophyll, but is the result of mal- 

 nutrition. 



The last theory of its function was advanced by Saccharoff 

 at the end of the century. Considering the action of 

 oxygen in the cell, and seeking for something universally 

 present therein which is capable of easy oxidation and 

 of yielding compounds which can be reduced again or 

 further decomposed with comparative ease, he held that 

 such processes may be readily carried out by minute traces 

 of iron. He put forward accordingly the hypothesis that 

 the various vital phenomena of protoplasm are set up by 

 the oxidation of a minute trace of iron contained in the 



