OF THE GREEN CELLS OF PLANTS 59 



tures, for many nucleins are iron- containing, and, as has been shown 

 by MacaUmn, after treating with acid alcohol to unmask the iron 

 previously present in an organic form, the chromatin of nuclei 

 always contains iron. 



The reactions for inorganic iron are shown most markedly with 

 the more lowly organised plants such as unicellular green plants 

 occurring alone or in lichens, or in delicate algal threads, but when 

 proper precautions are taken they can also be clearly demonstrated 

 in the chloroplasts of the higher plants. The reactions are particu- 

 larly well shown by the chloroplasts of aquatic plants, where, as is 

 well known, the percentage of iron in the ash is also high. 



These facts are in keeping with the natural order of evolution 

 and are also in accord with other observations. For example, 

 many algae (such as certain confervas and cladophora) deposit 

 around them a layer, yellow to rust-red in colour, consisting of 

 mixed ferrous and ferric oxides ; this is often actively secreted from 

 waters containing only traces of iron. 



A considerable number of lichens also secrete incrustations of 

 the mixed oxides of iron to such an extent as to change their appear- 

 ance to an iron oxide or ochre colour, so that they have been termed 

 by systematic botanists " formae oxydatae, ochraceae " or " iron 

 lichens." The iron oxide forms a fine incrustation usually on the 

 mycelium of the fungus. No association of this iron oxide with a 

 photo-synthetic function has ever been suggested, but in view of 

 our present knowledge of the photo- synthetic activity of iron salts 

 some investigation in this direction is highly desirable. It is an 

 interesting observation of Molisch, from our point of view, that these 

 " iron lichens " flourish exclusively on the oldest primitive rock 

 formations (" Urgestein "). They are never found upon chalk 

 formations, but grow upon granite, gneiss, syenite, and porphyry. 

 Molisch was unable to find inorganic iron in the other lichens, but 

 this doubtless arose from the less delicate methods he had at his 

 command at that time, and from the fact that the fatty bodies con- 

 tained in the green cells of the algae of the lichen had not been 

 removed. When the lichen is extracted with alcohol and Macal- 

 lum's haematoxylin test then applied, the algal cells rapidly stain a 

 deep blue-black, showing the presence of inorganic iron, while the 

 hyphae of the fungus only take on a brownish tinge during the same 

 time, and only give a faint positive reaction at the end of some days 

 or weeks. 



