Water in Plants 33 



Water in living plants. Water constitutes a large 

 proportion of the weight of all living plants, especially 

 during the period of active growth. The cured hay, as 

 any farmer's boy knows, weighs much less than did the 

 green grass when it was cut, and this loss in weight is due 

 almost wholly to evaporation of water from the tissues 

 of the plant under the influence of the sun and wind. 

 This water, which is contained in the tubes and inter- 

 cellular spaces of the stalk or leaf, is exactly the same 

 chemical compound as pure water found anywhere else, 

 and has no more value for the animal, 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, and 

 which has a peculiar nutritive value or function. Vege- 

 tation 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 min- 

 eral salts. When the plant is dried, these soluble com- 

 pounds do not pass off, but remain behind as part 

 of the dry matter. 



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 importance than is generally 

 recognized, because the food value of vegetable sub- 

 stances is influenced 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 



