812 POPULAR SCIENCE MONTHLY. 



of plants, and particularly in the green parts. Their habitual pres- 

 ence does not, however, authorize the conclusion that this metal is 

 necessary to the support and development of vegetable life. Some 

 substances, evidently indifferent, foreign, and even injurious, if they 

 exist abundantly in a soil, may be drawn into roots through the 

 movement of the sap, and fix themselves in various organs. This 

 occurs with copper in certain exceptional circumstances when the 

 soil is saturated with its compounds, and if such a condition should be 

 found to be repeated over a large extent of country, we might be 

 led, by analysis alone of its vegetable productions, to the false con- 

 clusion that copper was an essential or even necessary constituent of 

 them. But the value of the part performed by an element can not be 

 determined by analysis alone. Direct proofs are necessary for that, 

 methodical and comparative experiments in cultivation in mediums 

 artificially deprived or furnished with the element the importance of 

 which we wish to estimate. This has been done for combinations 

 of iron, and the utility of that metal, especially to the higher plants, 

 has been made thereby to appear. 



If iron is absent from the nutritive medium the plant will wither. 

 If we sprout seeds in a solution from which this metal has been care- 

 fully excluded, the development will follow its regular course as long 

 as the plant is in the condition properly called that of germination, 

 or while it does not have to draw anything from the soil. The stem 

 rises and the first leaves are formed as usual. But all these parts 

 will continue pale, and the green matter, the granulation of chloro- 

 phyll, will not appear. ]STow, if we add a small quantity of salt of iron 

 to the ground in which the roots are planted, or a much-diluted solu- 

 tion is sprinkled on the leaves and the stem, the chlorotic plant will 

 recover its health and take on its normal- coloration. Experiments of 

 this sort make well manifest that iron is necessary to green plants, 

 and they show, besides, the bearing of its action, and that what is 

 most special and most characteristic in the phenomena of vegetable 

 life may be traced exactly to the organization of that green matter. 

 It was long thought that if iron was necessary for the formation of 

 chlorophyll, it was because it had a part in its constitution. We 

 know now that this is not so. The metal does nothing but accompany 

 the chlorophyll in the granulation in which it is found. 



The influence which iron exerts in the development of the lower 

 plants, like the muscidenes, was illustrated with great precision in a 

 study made about thirty years ago by M. Raulin, who experimented 

 with the common mold {Aspergillus niger), to determine the coeffi- 

 cient of importance of all the elements that have a part in its vegeta- 

 tion. When the iron was removed from a medium that had been 

 shown capable of giving a maximum crop of that mold, the plants 



