The most recent observations on the roles of iron and manganese in plant metabolism are those of Shive (1941), Somers, Gilbert Shive (1942) and Somers and Shive (1942). These workers state that the theoretical explanation of the roles of manganese and iron in metabolic processes revolves round two facts: first, that the active functional iron is in the ferrous condition, and .
48 μg/g clearly showed that the increase of concentrations of manganese in plants was not directly related to traffic as the basic source. The manganese contents depend on plant species and have a wide range; in accordance with the data provided by Kárpáti et al. (1967) manganese contents in the dry matter of Lemna trisulca amounted to ppm and in Plantago .