190 ON THE COMPOSITION OF SOILS, &C. 



" important ingredient to the nourishment of 

 " plants, is earth : and of the different earths, the 

 " calcareous seems the most necessary, as it is 

 " contained in rain water ; and absolutely speak- 

 " ing, many plants may grow without imbibing 

 " any other ; M. Ruckert is persuaded that 

 " earth and water in proper portions, forms the 

 " sole nutriment of plants : but M. Giobert has 

 " clearly shown the contrary, for having mixed 

 " pure earth of alum, silex, calcareous earth, and 

 " magnesia, in various proportions, and moist- 

 " ened them with water, he found that no grain 

 " would grow in them ; but when moistened 

 " with water from a dung-hill, corn grew in 

 *' them prosperously; hence the necessity of the 

 '* carbonaceous principle is apparent." 



He also says, " Earths cannot enter into 

 plants, but in a state of solution ; or at least 

 " only when suspended with water in a state of 

 " division, as minute as if they really had been 

 " dissolved ; that siliceous earths may be sus- 

 " pended in such a state of division, appears 

 " from various experiments, particularly those 

 " of Bergman, who found it thus diffused in the 

 " purest waters of Upsal ; and it is equally cer- 

 " tain that it enters copiously into vegetables : 

 " both his experiments, especially those of Macci, 

 * establish this point beyond contradiction. Ar- 



