46 DEFINITION OF A PLANT. [u2CT. II. 



posed of simple earths devoid of animal and vege- 

 table matter in which plants will grow? And it 

 is well known that the presence of a large quan- 

 tity of salts, even of those kinds which, in small 

 quantities, promote vegetation, is more likely to 

 kill plants than to serve as nourishment to them. 

 A plant, it is true, may be reared in pure water, 

 or in pure powdered flints moistened with water ; 

 but in this case the water is the support of the 

 vegetable ; and we know that many animals, the 

 Infusoria, for instance, are nourished and support- 

 ed apparently in water alone. As this fluid is the 

 universal solvent, whatever it contains in solution 

 may be taken up by the vegetable vessels ; and 

 the experiments of Sir Humphrey Davy have 

 proved that even distilled water may contain both 

 saline and metallic impregnations : hence we can 

 conceive from what source the alkalies, salts, me- 

 tallic oxides, and earths, even silex, which are 

 found in vegetables, have been derived; but that 

 these are directly taken in as nourishment by 

 plants is not more likely, than that lime, which 

 forms so large a portion of the animal structure, 

 is, in its uncombined state, the food of animals *. 



* It is rather surprising that Sir Humphrey Davy, in his 

 late work on the Principles of Agriculture, adopts implicitly 

 the opinion of Mirbel, that saline substances form part of the 

 real food of plants ; particularly as he adds, " and supply that 

 " kind of matter which is analogous to bone in animals." Now 



