J54 CHYMISTRT APPLFED TO AGKICULTCTRE, 



io this kingdom : in vegetables the juices are carried mt& 

 the bark^ the alburnum, the pith, the wood, the leaves 

 and the fruit, by tubes and glands, which are arranged ia 

 hexagonal cells, and are very numerous in the parenchyma^ 

 and in the cortical layers of the bark : the juices undergo 

 particular modifications in the various organs, and form in 

 each one of them new compounds differing from each 

 other. 



The leaves receive the sap in vessels of the most delicate 

 texture ; in these it is elaborated, and combined with sub- 

 stances absorbed from the atmosphere, whilst the surplus of 

 water, as well as the oxygen of the carbonic acid from 

 which they have extracted the carbon, is given out by the 

 leaves through their transpiring pores. The sap, after exr 

 periencing these changes, passes into the organs of the 

 plant, where it is subjected to new elaborations. 



The leaves are to plants what the lungs are to animals > 

 those receiving the sap, as these do the blood, to be mingled 

 in them with the gas absorbed from the atmosphere, and to 

 pass thence into the great vascular system; and from both 

 leaves and lungs the superfluous water and gases are thrown 

 out into the air. 



We likewise find a great variety of structure amongst 

 the various species of which the two kingdoms are com- 

 posed ; some have a soft, loose, parenchymatous formation ; 

 others present a harder and dryer tissue ; this, in vegetables, 

 is owing to the predominance of carbon ; in animals, to that 

 of phosphate of lime^ these two principles, though very 

 different, form the basis of their separate structures. The 

 same elements enter into the composition of all the products, 

 whether animal or vegetable ; the difference between them 

 arising solely from the different proportions of the constitu- 

 ent principles. 



An analysis of the principal products of vegetation has 

 been made with great care by Messrs. Gay-Lussac and 

 Thenard. The results of these researches enable us already 

 to draw some conclusions in regard to the character of any 

 one of the products, according as this or that principle may 

 predominate in its composition ; or according to the nature 

 of the elements combining to form it. Thus we know, 



1. That a vegetable substance is acid when it contains 

 BO azote, and when the quantity of oxygen in proportion to 

 that af hydrogen, is greater than is necessary for the formap' 

 ion of water 



