CHAP, iv The Ash of Plants 365 



material for the construction of nuclei and of chloroplasts. 

 Mangin, in 1892, showed that it is a constituent of certain 

 parts of the structure of the cell wall, being in combination 

 with one of the pectic acids. 



Magnesium was first shown by Salm-Horstmar to be 

 an essential element for the green plant, but very little 

 has since been discovered as to the part it plays. Schmiede- 

 berg showed in 1877 that the protein crystals of the brazil- 

 nut are composed of a magnesium compound of vitellin, 

 and Griibler, in 1881, found that the crystallizable protein 

 of the gourd contains the metal. Like calcium, therefore, it 

 appears to form compounds with protein. In 1883 Raumer 

 stated that it is concerned with the transportation of starch 

 from the chloroplast. 



_Iron has been the subject of much inquiry since Gris, in 

 i843,showeoTits^presehce to be necessary for the formation 

 of chlorophyll. Its association with this pigment led to 

 the opinion that it must enter into its molecule, and Hansen, 

 in 1889, claimed to have found it there. Schunck, in 1891, 

 said he found it in the ash of phylloxanthin, which is one 

 of the products of the decomposition of chlorophyll. On 

 the other hand, in 1892, Gautier, whose analyses of the 

 pigment were made with great care, failed to find any iron 

 in the ash, and its absence was claimed by Ernich and by 

 Molisch in the same year. Macallum failed to find it in 

 the chloroplasts by micro-chemical methods in 1891. Raulin 

 in 1869, and later both Molisch (1892) and Benecke (1895) 

 showed it to be essential to the nutrition of fungi. 



Observations as to the disposition of iron in the plant 

 led to its identification as a constituent of the chromatin 

 of the nucleus. This discovery was due to Macallum and 

 his co-workers in America. In 1891 Bensley, by micro- 

 chemical methods devised by Macallum and working with 

 him, found it in the chromatin of the pollen cells of Dian- 

 thus, Cucurbita, and Narcissus, both in the mitotic figures 



