AGRICULTURAL CHEMISTRY. 



121 



At one or several places, the formative 

 layer is thickened to the so-called nucleus, 

 (a fig. 2) the point from which growth 

 and transformations proceed. Within 

 the cell thus constructed exists a liquid, 

 the cell-contents, from which, in course 

 of time, solid cell contents of various 

 character are found todevelope. 



In a chemical sense, not less than in a structural, the single globu- 

 lar cell is the type of all vegetation. 



The outer wall of the cell is formed of that material which is 

 itself the most abundant product of vegetable life, and which rep- 

 resents an important group of bodies, that are familiar to all, as large 

 ingredients of our daily food. 



The table wdiich here follows gives the names and the chemical 

 formulae of what we may term the cellulose group or the vegetal 



CARBO-HYDRATES. 



^12 



c 12 

 c 



12 



H, 



<>, 



(\ 



H, 



0, 

 0, 



Cellulose 



Starch 



Inulin 



Dextrin 



Gum 



Cane sugar 



Fruit sugar 



Grape sugar 



Cellulose is the body already alluded to as constituting the material of 

 the outer coating of the cells. It often accumulates in some parts of 

 the plant by the thickening of the cell 

 walls, thus forming the greater share 

 of the wood (fig. 4) of trees and shrubs. 

 Linen,hemp,(Bfig.3) and cotton (Afig. 

 3)are nearly or quite pure cellulose. It 

 exists largely in the stones or shells of r^ 

 fruits and nuts. The so-called vege- \ | \ 

 table ivory is chiefly a very compact 

 form of cellulose. In general, this 

 proximate organic element is the 

 frame-work of the plant, and the 

 material that gives toughness and 

 solidity to its parts. 



Cellulose is characterized by its 

 great indifference to most ordinary 

 solvents. Water, alcohol, &c, do 

 not dissolve it, and the stronger rea- 

 gents of the chemist rarely take it 

 up without occasioning essential 

 changes in its constitution.* With 

 strong nitric acid it yields nitre-eel- 



s' According to Pelouze, cellulose is dissolved by strong hydrochloric acid, and separates 

 again in part (part is converted into sugar) on dilution. Schweitzer has recently made the 



