COMPOUNDS OF NUTRITION 31 



animal than water from any other source excepting that 

 it is pure and is not subject to the contamination which 

 sometimes occurs in streams and wells. There is no such 

 thing as the so-called natural water of plants, which has 

 a peculiar nutritive value or function. 



38. Sap or plant juice. — ^Vegetation water should be 

 distinguished from sap or plant juice. Sap is more than 

 water; it is water holding in solution certain substances 

 such as sugars and mineral salts. When the plant is 

 dried, these soluble compounds do not pass off, but remain 

 behind as part of the dry matter. 



39. Proportion of water in plants. — ^The proportion of 

 water in plants varies greatly in different species, and in 

 the same species according to the stage of growth or the 

 surrounding conditions. These facts have more impor- 

 tance than is generally recognized, because the food 

 value of vegetable substances is largely determined by the 

 proportion of dry matter. It is always necessary to know 

 the percentage of water in a green plant before we can 

 estimate its worth for feeding purposes. 



The variations in water-content of the living tissues of 

 different species of plants or parts of plants are well illus- 

 trated by the following average figures: (See Pars. 304- 



303.) 



Tabi^ VI. Wateb in Geebn Plants Percent 



Pasture grass (mixed) . . .... 80. 



Timothy grass ... .61.6 



Oats (fodder) . 62.2 



Rye (fodder) ■ 76.6 



Sorghmn (fodder) 79.4 



Fodder com, dent, kernels glazed . • 73.4 



Red clover ■ • 70.8 



Alfalfa 71.8 



Horse-bean ... 84.2 



Potatoes (tubers) 78.9 



Turnips 90.5 



