560 Prof. B. Moore. Presence of Inorganic Iron 



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 produce chlorophyll when exposed to light but 

 contain yellow chromatoplasts, 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.* 



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

 mental 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 considerable 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 Grisf 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 

 10 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.* Molisch§ 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 as the reserve store of iron always contained in the 

 seed embryo and cotyledons has been exhausted in the primordial leaves, only 

 chlorotic pale-yellow leaves are formed. These pale-yellow leaves rapidly 

 turn green if minute quantities of an iron salt are added to the culture fluid, 

 or even if the surface of the leaf be painted over with a dilute solution of an 

 iron salt, as had been previously shown by Gris to be the case with 



* Quoted by Czapek, ' Biochemie der Pflanzen,' vol. 1, p. 447. 



t ' De l'Action des Composes Ferrugineaux sur la Vegetation,' 1843. See also ' Comptes 

 Rendus,' vol. 19, p. 1118 (1844) ; vol. 21, p. 1386 (1845) ; vol. 23, p. 53 (1846) ; and vol. 25, 

 p. 276 (1847). 



\ Salm Horstmar, 'Versuche iiber die Ernahrung der Pflanzen,' 1856; A. Gris, 

 'Annales d. Scien. Nat.,' Series IV, vol. 7, p. 201 (1857); Sachs, 'Flora,' 1862. 



§ Molisch, 'Die Pflanzen in ihren Beziehungen zum Eisen,' Jena, G. Fischer (]892). 

 Many of the references given are quoted from this source. 



