CHAPTER VII. 



* 



VEGETABLE PRODUCTS. 



281. The vegetable is the laboratory in which the materials 

 of all organic products are, in the first place, prepared. The 

 animal has no power to convert inoi'ganic elements into organic. 

 All come through the agency of plants. 



Vegetable products are naturally divided into two great classes. 

 1st, Those into whose composition Nitrogen enters ; and 2d, 

 Those which contain no Nitrogen. 



282. The substances that compose the second class make up 

 the great mass of vegetation. 



This class may be conveniently studied under the following 

 divisions : 1st, Such as contain Oxygen and Hydrogen, in pro 

 portions to form water, as Starch, Gum, Sugar, &c. ; 2d, Acids, 

 containing usually more Oxygen than Hydrogen, by atoms ; 3d, 

 Oils, containing more Hydrogen than Oxygen. 



283. Cellulose (Lignin, vegetable fiber), 0,2, Hio, 0,o, is the 

 most abundant vegetable product. It forms the basis of all 

 vegetable structures. It is the original membrane that forms 

 all the vessels of the plant. Other materials may be deposited 

 on it which greatly modify the various tissues, especially the 

 cellular. 



It is insoluble in alcohol, water, ether, dilute acids or alkalies. 

 It is soluble in concentrated sulphuric acid. Bleached paper, 

 linen, and cotton are nearly or quite pure cellulose. It is made 

 to resist the action of external agents when it constitutes wood, 

 by soaking the wood in various saline solutions, or by charring. 

 Charred wood has been known to last thousands of years. Per- 

 fect dryness and exclusion from the air prevent the decay of 

 wood. Low temperature has also great efiect in the preservation 

 of wood, when the other agents are present. Poplar, in the 

 Mammoth Cave of Kentucky, at a uniform temperature of 5*7°, 

 is undecayed after nearly 50 years, when the same wood, exposed 

 on the surface, will decay in three years. 



The different kinds of wood vary remarkably in the time they 



281. What is the vegetable? What two classes of vegetable products? 

 —282. What subdivirtion of the second class ?— 283. What is cellulose? 

 What does it form ? What are its properties ? What are nearly pure cel- 

 lulose ? How made to resist the action of external agents ? W h'y does sop- 

 wood decav sooner than heart-wood ? 



