INORGANIC CONSTITUENTS OF PLANTS. 169 



of the same species of tree from Mont La Salle. The potash 

 and lime also varied in the two localities. This is accounted 

 for by the fact, that one inorganic base may be substituted 

 for another, in an isomorplwus proportion. If, therefore, 

 there is not in a soil that inorganic base which the plant most 

 likes, it will take up a quantity of some other base. There 

 is, however, some inorganic base, which a species of plants 

 prefers to any other, and if that is entirely absent, in some 

 cases the plant will be imperfect or fail to grow altogether, 

 while in others it will be diminished in some of its pro- 

 ducts. As these bases are combined with inorganic, and al- 

 so with organic acids, and as it is only with the latter that 

 substitutions can be made, when one base is substituted for 

 another, a different quantity will be employed, because one 

 equivalent of base must be substituted to saturate the acid, 

 and the combining ratios differ in different bases. But still 

 there is a remarkable law in reference to the quantity o^inetal- 

 lic oxides or inorganic bases in all these substitutions, the 

 quantity of oxygen is exactly the same ; that is, there is an 

 equal number of equivalents of metallic oxides, whatever sub- 

 stitution may be made. Hence, if the soil does not contain 

 one kind of base, it is not on that account barren, but an- 

 other may supply its place. But notwithstanding this fact, 

 some bases exert a better injluence upon the development 

 of plants than others. For example, phosphate of magnesia, 

 in combination with ammonia, is found invariably in the seeds 

 of all kinds of grasses. It is contained in the outer, horny 

 husk, and is introduced into the bread with the flour, although 

 the bran contains the larger quantity of it. Hence, this 

 substance is necessary to the perfect development of the 

 grasses and grains. It would also be next to impossible to 

 raise wheat without potash. 



There are, moreover, certain species of plants, which re- 

 quire certain alkalies for their growth ; such as the sea-plants. 



