QUANTITATIVE RELATIONS. 201 



Risse, under Sachs' direction, {Exp. Physiologie, 143,) 

 demonstrated that manganese cannot take the place of 

 iron in the office just described. 



Functions of other Ash-Ing^rcdients. — As to the spe- 

 cial uses of the other fixed matters we know little. It ap- 

 pears to be proved beyond doubt that potash, lime, and 

 magnesia, are indispensable to the life and health of ani- 

 mals, and since all animals derive the chief part of their 

 sustenance from the vegetable world, it is obvious that 

 these substances must be ingredients of plants in order to 

 fit the latter for their nutritive office ; but why no vegeta- 

 ble cell can be elaborated without potash, why lime and 

 magnesia are imperative necessities to plants, we are as 

 .yet not able to comprehend. 



CHAPTER ni. 



QUANTITATIVE RELATIONS AMONG THE INGREDIENTS 

 OF PLANTS. 



Various attempts have been made to exhibit definite 

 numerical relations between certain different ingredients 

 of plants. 



Equivalent Replacement of Bases.— In 1840, Liebig, 

 in his Chemistry applied to Agriculture, suggested that 

 the various bases might displace each other in equivalent 

 quantities, i. e., in the ratio of their molecular weights, 

 and that were such the case, the discrepancies to be observ- 

 ed among analyses should disappear, if the latter were in- 

 terpreted on this view. Liebig instanced two analyses of 

 the ashes of fir-wood and two of pine-wood made by Ber- 

 thier and Saussure, as illustrations of the correctness of 

 this theory. In the fir of Mont Breven, carbonate of 

 9* 



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