QUANTITATIVE RELATIONS. 201 
Risse, under Sachs’ direction, (Hap. Physiologie, 143,) 
demonstrated that manganese cannot take the place of 
iron in the office just described. 
Functions of other Ash-Ingredients,—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 IL 
§ 1. 
QUANTITATIVE RELATIONS AMONG THE INGREDIENTS 
SS 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 
g* 
