56 IRON COMPOUNDS IN THE CHLOEOPLASTS 



important facts : first, that the chloroplast alone, even when dis- 

 placed from the rest of the cell, can, in presence of light, go on syn- 

 thesising and producing oxygen ; and, in the second place, a still more 

 important point in our chain of evidence namely, that certain 

 leaves such as those of the yellow variety of elder, which do not pro- 

 duce chlorophyll when exposed to light but contain yellow chroma- 

 toplasts, cause synthesis and produce oxygen. These observations 

 as to synthesis by healthy yellow leaves have been confirmed by 

 other observers such as Tammes, Josopait, and Kohl. 1 



The strongest piece of evidence, however, that iron salts are more 

 fundamental to photo- synthesis and take an earlier share in it 

 than chlorophyll, is that furnished by that process frequently 

 occurring in green leaves known as " chlorosis." 



Chlorosis is a pathological condition of green leaves of consider- 

 able practical importance in arboriculture, and the discovery of its 

 cause is, as Molisch states, one of the most interesting and beautiful 

 in the history of plant physiology. 



It was shown in 1843 by Eusebe Gris 2 that chlorosis naturally 

 occurring in the leaves of shrubs or trees could be entirely removed 

 either by applying dilute solutions of iron salts to the roots, or by 

 placing the detached chlorotic branch in a dilute solution of iron, 

 or even by painting the chlorotic leaf with a very dilute solution 

 of an iron salt. In some cases within 24 hours, and in nearly all 

 cases in a period of a week to ten days, the green colouring matter 

 developed in the leaves where none had been before. 



These results have been often confirmed and have been extended 

 by Salm Horstmar, A. Gris, and Sachs. 3 Molisch 4 has, moreover, 

 shown in a long series of experiments with different species of 

 plants that all green plants, even when fully exposed to light, become 

 afflicted with chlorosis and fail to develop chlorophyll when they are 

 grown in a culture fluid especially made devoid of iron. As soon 



1 Quoted by Czapek, "Biochemie der Pflanzen," vol. i., p. 447. 



2 " De 1'Action des Composes Ferrugineaux sur la Vegetation," 1843. See 

 also Comptes Eendus, vol. xix., p. 1118 (1844); vol. xxi., p. 1386 (1845); 

 vol. xxiii., p. 53 (1846); and vol. xxv., p. 276 (1847). 



3 Salm Horstmar, "Versuche iiber die Ernahrung der Pflanzen," 1856; 

 A. Gris, Annales d. Scien.Nat., Series IV., vol. vii'., p. 201 (1857); Sachs, 

 "Flora,"' 1862. 



4 Molisch, "Die Pflanzen in ihren Bsziehungen zum Ehen," Jena, 

 G. Fischer (1892). Many of the references given are quoted from this 

 source. 



