IRON AND ZINC NECESSARY FOR PLANTS. 69 



should the conjecture prove true that iron is a constant 

 constituent of chlorophyll and of the leaves of many 

 flowers, it may be assumed that other metals, found in- 

 variably present in certain varieties of plants (as man- 

 ganese in Pavonia, Zostera, Trapa natans, in many 

 ligneous plants, several cereals, and in the tea shrub), 

 take part in the vital functions, and that certain pecu- 

 liarities depend upon the presence of those metals. The 

 ash of Viola calaminarw, a plant which, in the parts 

 about Aix-la-Chapelle, is held so strongly indicative of 

 the presence of zinc, that the places where it grows are 

 selected for opening new mines in search of zinc ore, is 

 found to contain oxide of zinc. (Alex. Braun.) 



As chloride of sodium and chloride of potassium 

 cause some plants to thrive, so iodide of potassium 

 manifestly performs a similar part in others ; and if 

 one plant may properly be called a chlorine plant, 

 others may with equal propriety be termed iodine 

 plants, or manganese plants.* (Prince Salm-Horst- 

 mar.) 



The diversity in the amount of iodine in different 

 varieties of fucus (Gocdechens), or of alumina in various 

 kinds of Lycopodium (Count Laubach), remains, indeed, 

 unexplained ; but the power of plants to withdraw sub- 

 stances like iodine, even in the smallest quantities, from 

 the sea water in which they grow, and to accumulate 

 and retain them in their organism, can only be ex- 

 plained upon the assumption that these substances have 

 entered into combination with certain constituent parts 

 of the plants, whereby as long as the plant lives they 

 are prevented from returning to the medium from 

 which they were taken.f 



* The examination of the following water-plants revealed the presence 

 of considerable quantities of manganese and iron in their ash, though the 

 water in which they grew apparently contained no trace of manganese : 

 Victoria regia (in the leaf-stalk principally manganese, in the leaf iron) ; 

 Nympkcea ccerulea, dentata, lutea ; Hydrocharis Humboldti ; Nelumbiwn 

 asperifolium. (Dr. Zoller.) 



f With respect to the copper in the grains of wheat and rye, which 

 Meier of Copenhagen has shown to be a constant constituent of both seeds, 

 Forchhammer (PoggendorfTs ' Annal.' xc. 92) remarks : ' It is an old and 



