15 



tbat phosphoric acid can not be replaced by liypophosphoric acid. 

 The writer has observed that algie are at least not injured by a 1 

 per niille solution of sodium hypophosphite, phosphite, or pyro and 

 mcta phosphate, and the two last-mentioned salts can even be well 

 utilized by mold fungi.' The assertion once made that phosphoric 

 acid in alga^ may be replaced by arsenic acid is absurd and moreover 

 Molisch had shown it to be impossible. 



THE PHYSIOLOGICAL ROLE OF IRON COMPOUNDS. 



RELATION BETWEEN THE COLORINCr MATTER OF THE BLOOD AND 



OF THE LEAF. 



Iron compounds are indispensable for the production of the chloro- 

 phyll' of tlie plant and the ha-moglobiu of the red blood corpuscles 

 of the higher animals. Without the former there is no assimilation of 

 carbonic acid, hence no synthesis of organic matter in the green plant, 

 and without the latter no respiration of the vertebrates, since it is the 

 hiemoglobin that carries the molecular oxygen to the remotest regions 

 of the body. Although the chlorophyll itself does not contain iron, 

 haemoglobin contains it as an essential constituent in the molecule. 



There is evidently a close relation between the coloring matter of the 

 leaf and that of the blood. The phylloporphyrin obtained from chloro- 

 phyll by the action of alkalies shows almost the same spectrum as the 

 hfematoporphyrin obtained from the ha-moglobin of the blood. Hajma- 

 toporphyrin seems to correspond to a dioxyphylloporphyrin, and both 

 of these compounds appear to be derivatives of pyrrol. It was espe- 

 cially the investigations of Nencki and of Tschirch that first directed 

 attention to the analogies between these two physiologically important 

 bodies. 



INFLUENCE OF IRON AND OTHER MINERAL NUTRIENTS ON THE 



FORMATION OF CHLOROPHYLL. 



Iron is not the only requisite for the production of chlorophyll. 

 Other mineral nutrients are not less necessary, and above all only a 

 normal plastid can produce the green color with the aid of iron salts and 

 thus become a chloroplast; hence cases of imperfect i^lastids may occur, 

 e. g., where an increased supply of lime is required to produce normally 

 green leaves. A case where phosphoric acid was required in addition 

 to the iron to produce the chlorophyll was observed by the writer in 

 the case of an alga. Some threads of Spirogyra majuscula were placed 



'Bot.Centralbl.,1895. 



2 An observation on chlorophyll made by the writer may here be mentioned, as it 

 places the great sensibility of this substance toward chemical reagents beyond a 

 doubt. When Spironyra threads are treated with moderately concentrated hydro- 

 chloric acid, they at once assume a yellowish color, but soon afterwards turn to a 

 bluish green, which points to two successive changes and indicates that in the 

 preparation of pure chlorophyll strong acids have to be avoided. Various discrep- 

 ancies in the observations of different authors may be traced to this circumstance. 



