THE INORGANIC ELEMENTS. 5 



quantities of water in their tissues. In one hundred parts of Cerate" 

 phyllum demersum ninety were found to be water, and ten solid 

 matter. 



Carbonic acid is also widely diffused with water : it forms the principal 

 source of nourishment for plants. It is found dissolved in the sap of 

 plants : at night, in almost every plant; in the day, in ripe fruits, in aerial 

 roots, &c. In consequence of the processes of respiration and combus- 

 tion on the earth, and volcanic agency, the atmosphere contains an inex- 

 haustible supply of carbonic acid for plants. 



Oxalic acid is constantly produced by the decomposition of the fore- 

 going compounds, and is found apparently in all plants. It is found 

 free in most succulent plants, as the Crassulacece, Ficoidece, Cactacece*, 

 &c. ; also in the hair-glands of Cicer arietinum* 



b. Compounds with Hydrogen. These are principally ammonia 

 (NH 3 ), hydrochloric, hydriodic, and hydrobromic acids* 



Ammonia is probably the source of nitrogen in all plants. It occurs 

 free in the unassimilated sap, as in. the spring sap of the birch and the 

 grape vine, and perhaps also in the tissues of unnaturally succulent 

 cultivated plants, as the beet. 



7. The foregoing oxides and acids unite together to form salts, 

 some of which are found dissolved in the sap of plants, and others 

 in the form of crystals. The most important are the alkalies in 

 combination with the vegetable acids, or chlorine, bromine, and iodine ; 

 then, perhaps, those with sulphuric and phosphoric acids ; whether 

 any exist with carbonic acid, is doubtful : next come the earths, 

 with vegetable acids, especially oxalic acid, then with sulphuric and 

 phosphoric acids; and, lastly, the metals mostly in combinations 

 not yet determined. The greater part of the salts are found in 

 the living, vegetating, green parts of plants, as the leaves, &c. ; 

 the least, in the wood (Saussure). A certain quantity of these 

 salts appears essential to the life of plants. Ammoniacal salts from 

 the atmosphere appear to be the source of the nitrogen in plants. 



Fourcroy and Yauquelinf, long ago, proved that the greater part of 

 the carbonates found in the ashes of plants were formed, during the burn- 

 ing, from other salts of vegetable acids. They proved that almost all 

 plants contain 1. acetate and malate of lime dissolved in the sap; 

 2. citrate and tartrate of lime, which either exist as a super salt or 

 in a solid form ; 3. oxalate of lime in a solid form. All these are 

 found in the ashes of plants as carbonates ; but these latter are not to 

 be found if, before the burning, the plants are by turns treated with 

 cold and boiling water and diluted muriatic acid. 



The salts of the alkalies are found dissolved in plants, but the 

 insoluble earthy salts present themselves in a crystallised form in the 

 cells. Of these, the oxalate of lime has been most accurately inves- 



* Liebig (Annal. xlvi. p. 77.) says the Cactacece contain tartaric acid; but he is 

 certainly wrong with regard to most Cactacece. 



f De la Metherie, Journ. de Physique et de Chim., tome Ixviii. p. 429. (1809). 



B 3 



