CONSTITUENTS OF PLANTS 361 



tains only relatively small quantities 1 of sugars and starches, and 

 large amounts of less easily digested material. 



The nitrogen-free extract makes up the largest part of most 

 agricultural plants. In many instances it is as much as the sum 

 of all the other constituents. The percentages in the dry matter 

 of certain plants are given in the following table : 



NITROGEN-FREE EXTRACT. (!N DRY MATTER.) 



Per cent. 



Corn fodder 60.6 



Timothy hay 52.8 



Red clover 45.8 



Cowpea vines 43.6 



Potatoes 82. 2 



Corn 77.4 



Wheat 80.4 



Co wpeas 65. 5 



Soja bean 32.2 



The nitrogen- free extract may contain sugars, starches, pen- 

 tosans, hemi-celluloses, gums, vegetable acids, and miscellaneous 

 bodies. It is composed to a large extent of carbohydrates. 



Carbohydrates are compounds containing carbon, united with 

 hydrogen and oxygen in the proportion to form water. 

 Chemically, they are related to alcohols and aldehydes or ketones. 

 The general formula of carbohydrates is Cm(H 2 O)n. Glucose, 

 CgH^Oe, starch C 6 H 10 O 5 , and cane sugar (sucrose) C^H^On, 

 are examples. Some carbohydrates are soluble in water 

 and have a sweet taste, others are insoluble and taste- 

 less. Some are easily acted upon by chemical reagents, 

 while others, (particularly cellulose) are very resistant. All 

 carbohydrates, however, may, by appropriate means, be converted 

 into simple sugars. 



It is not correct to use the term "carbohydrates" to signify the 

 nitrogen-free extract. The nitrogen-free extract consists partly 

 of substances other than carbohydrates. Crude fiber also con- 

 tains cellulose, which is a carbohydrate. 



Sugars. The sugars are carbohydrates which are soluble in 

 water, and, as a general rule, have a sweet taste. Cane sugar, 

 1 Frear, Report Pennsylvania Station, 1903-4. 

 24 



