58 IRON COMPOUNDS IN THE CHLOROPLASTS 



alcohol used in the first extraction of the leaf, 1 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 the older the leaf is the more iron does it 

 contain in its ash. Thus Boussingault found in the ash of young 

 leaves of Brassica 2 per cent, of Fe 2 3 , while old leaves contained 

 in their ash 9-64 per cent. Lactuca saliva had in the young leaves 

 2-67, and in the old leaves 643 per cent, of Fe 2 3 in the ash. Another 

 point is the curious conservation, resembling that seen in the animal 

 economy, of the iron of the leaf in the case of deciduous leaves. 

 Before the leaf drops a good deal of the iron is reabsorbed and stored 

 for future use. This is shown by analyses of the iron of the leaves 

 of Fagus sylvatica made by Rissrnuller 2 in successive months. The 

 figures quoted give quantities of Fe 2 3 in 100 parts of dried leaves 

 collected at the times of year stated : 



May. June. July. Aug. Sept. Oct. Nov. 

 Oxide of iron . . 0-35 0-51 0-58 0-75 1-03 0-60 0-59 



The gradual increase of iron content to a maximum followed 

 by a fall as the leaves grow sere is very interesting. 



It has been shown by Molisch (loc. cit.) that iron is an essential 

 constituent for the growth of all plants, whether green or otherwise, 

 but the saprophytic and parasitic plants which contain no chloro- 

 phyll require much less iron and, as a rule, contain much less in their 

 ash. Our own experiments show that the histochemical reactions 

 for iron develop much more slowly in the fungi and are much less 

 intense in degree. These feebler reactions probably arise from 

 organic compounds of iron slowly being decomposed in traces and 

 setting free ionic iron. These organic iron compounds of the fungi 

 are concerned with some other function than photo- synthesis or 

 chlorophyll formation; they probably take a part in nuclear struc- 



1 According to early observations of Boussingault (Agronomic, vol. v., 

 p. 128) from one-quarter to one-third of the iron is removed by the alcohol. 



2 " Ueber die Stoffwanderung in der Pflanzen," Landw. Versuchsstationen, 

 1874 (Just's Jahresbericht, vol. ii., p. 849, 1874). 



