68 CHYMISTRY APPLIED TO AGRICULTURE. 



experiments of Davy, contains some alkaline and earthy 

 atoms. 



Messrs. Schrader and Braconnot have published the re- 

 sults of their experiments, by vi^hich they have been led to 

 believe, that salts and earths are created in the organs of 

 plants; but M. Lassaigne has proved, that the salts and 

 earths, contained in the developed plant, are the same as 

 those that are found in the seed from which they sprang. 



M, Th. de Saussure, whose opinion upon these matters 

 is of great weight, has proved that plants do not create any 

 of these substances. 



Besides, if the formation of certain salts be a power of 

 the plant itself, why does not the salsola afford more ma- 

 rine salt when it grows at a distance from the sea ? Why, 

 under the same circumstances, does not the " tamarisk" 

 furnish more sulphate of soda? and, finally, why does the 

 turnsol remain destitute of salt-petre, if raised upon a soil 

 which does not contain it? 



Be this doctrine as it may, there are two practical truths 

 which we do know ; the first is, that certain salts enter, 

 if I may so speak, as natural elements into the composition 

 of some plants; since it is found that they languish 

 in earths not containing those substances; and that the 

 plants absorb them abundantly, when they are present. 

 The second is, that the salts ought always to be united with 

 manures ; the excellence of which is increased, in propor- 

 tion to the quantity they contain, provided it do not exceed 

 the wants of the plants, and that the action be not too 

 energetic. 



I may add, that a plant absorbs, from preference, the 

 salt most analogous to its nature. The salsola, which 

 grows by the side of the tamarisk, sucks up from the earth 

 marine salt; whilst the tamarisk imbibes from it the sul- 

 phate of soda. It is proved by the analysis of plants of 

 different kinds, that have been raised upon the same 

 ground, that they do not furnish the same salts, or that, at 

 least, they present a great difference in the quantities they 

 contain. 



The salts are necessary to plants ; they facilitate the ac- 

 tion of their organs so much, that they are often employed 

 without mixture. 



Limestone submitted to the action of fire loses the car- 

 bonic acid, which is one of its constituent principles, and 



