IRON NECESSARY FOR PLANTS. 57 



Those mineral substances which, hke iron, are constant 

 constituents of all plants, though ])resent only in very 

 small proportions, must be regarded very differently from 

 those metals which Forchhammer found in woody plants. 



We know the part which iron performs in the animal 

 organism, in which it is present in comparatively no larger 

 quantities than in the seeds of cereals ; and we are fully 

 convinced that, without a certain amount of iron in the 

 food of animals, the formation of the blood corpuscles, the 

 agents of one of the chief functions of the blood, is im- 

 possible. Hence, by the law of dependence, which hnks 

 together the hfe of animals and plants, we are compelled 

 to ascribe to the iron in the plant also an active part in 

 its vital functions so material that the absence of that 

 metal would endanger the very existence of the plant. 



Hitherto chemistry has attributed a positive part in the 

 vital process of plants to those incombustible substances 

 only wdiich are common to all, and which differ only in 

 the relative proportions in the plants. But 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 invariably present in 

 certain varieties of plants (as manganese in Pavonia, 

 Zostera, Trapa natans^ in many ligneous plants, several 

 cereals, and in the tea shrub), take part in tlie vital func- 

 tions, and that certain pecidiarities depend upon the pre- 

 sence of those metals. Tlie ash of Viola calaminaria, a 

 plant which, in the parts about Aix-la-Chapelle, is held so 

 strongly indicative of the presence of zinc, tliat the places 

 where it grows are selected for opening new mines in 

 search of zinc ore, is found to contain oxide of zinc. 

 (Alex. Braim.) 



As cldoride of sodinm and chloride of potassium cause 

 some plants to thrive, so iodide of potassium manifestly 



