THE VOLATILE PART OF PLANTS. 55 



the door is closed, and the water is brought to boil by the heat of a lamp 

 or stove. The precise quantity of water belonging to, or .contained in, a 

 substance, is ascertained by first weighing the substance, then drying it 

 until its weight is constant. The loss is water. 



In the subjoined table are given the average quantities, per cent, of 

 water existing in various vegetable products when air-dry. 



WATER IN AIR-DRY PLANTS. 



Meadow grass, (hay,) 15 



Red clover hay 17 



Pine wood 20 



Straw and chaff of wheat, rye, etc 15 



Bean straw 18 



Wheat, (rye, oat,) kernel 14 



Maize kernel 12 



That portion of the water which the fresh plant loses by 

 mere exposure to the air is chiefly the water of its juices 

 or sap, and is manifest to the sight and feel as a liquid, in 

 crushing the fresh plant; it is, properly speaking, the free 

 water of vegetation. The water which remains in the air- 

 dry plant is imperceptible to the senses while in the plant, 

 can only be discovered on expelling it by heat or other- 

 wise, and may be designated as the hygroscopic water of 

 vegetation. 



The amount of water contained in either fresh or air- 

 dry vegetable matter is constantly fluctuating with the 

 temperature and the dryness of the atmosphere. 



2. THE CELLULOSE GROUP, OR THE AMYLOIDS. 

 This group comprises Cellulose, Starch, Inulin, Dextrin, 

 Gum, Cane sugar, Fruit sugar, and Grape sugar. 



These bodies, especially cellulose and starch, form by 

 far the larger share perhaps seven-eighths of all the dry 

 matter of vegetation, and most of them arc distributed 

 throughout all parts of plants. 



Cellulose, C ia H 20 O 10 . Every agricultural plant is an 

 aggregate of microscopic cells, i. e., is made up of minute 

 sacks or closed tubes, adhering to each other. 



