( 22 ) 

 stances, is well attested by the agricultural ex- 

 periments and conclusive analyses of Bous- 

 singault. Thus, some plants imbibe salt upon 

 the same soil where others take up none or 

 but small quantities. Pellitory, nettle, bo- 

 rage, covetous of nitrates, select them from 

 the soil, while other plants growing by their 

 side contain only traces of them. Wheat 

 upon the same land takes up eight times more 

 phosphoric acid than beets or turnips ; oat and 

 wheat straw contain fifty or sixty times more 

 silica than the oats and wheat themselves. 

 These are only a few of a number of conclu- 

 sive examples that could be cited. On the 

 other hand, it is well known that plaster is fa- 

 vourable to the leguminous plants, and Bous- 

 singault has shown that it produces no effect 

 upon wheat. It is known also that certain 

 plants prefer particular kinds of soil on ac- 

 count of the principles which they contain ; 

 thus the fern, chestnut, and the vine, require 

 salts abundant in potassa. 



These multiplied facts prove, as Gasparin 

 well says, that it is not a definite amount of 

 any one nutritive principle, but the choice of 

 several different ones, which is required for 

 plants. We do not mean to say that the 



