ORGANIC COMPOUNDS OF PLANTS 197 



The term nitrogen-free extract means that the bodies 

 contain no nitrogen ; they are nitrogen-free or non-nitroge- 

 nous, and are soluble in dilute acids and alkalies. The 

 nitrogen-free extract of wheat is composed mainly of 

 starch ; in some foods, as carrots, it is largely sugar. In 

 human foods, the nitrogen-free extract is composed 

 mainly of carbohydrates as starch and sugar, while in 

 animal foods, it consists of pentoses and a large number 

 of compounds dissimilar in character and food value. In 

 plant bodies, the nitrogen-free extract usually constitutes 

 the largest of any of the groups of compounds. Meats 

 and animal products, except milk, contain only very 

 small amounts. 



Fats 



260. Presence in Plants. Fats and oils form one of 

 the subdivisions of the non-nitrogenous compounds of 

 plants. Fat is present in nearly all plants, but in smaller 

 amounts than the carbohydrates. The fat in plants is 

 produced from starch. For example, in flax, there is 

 more starch than fat when the plant is growing, but in 

 the mature plant, there is more fat than starch, due to the 

 starch being converted into fat. This change of starch 

 to fat can take place only in the plant cells ; fat, as yet, 

 cannot be made synthetically. During the process of 

 germination, the fat of seeds is changed back to starch. 

 While fat is present in nearly all parts of plants, it is 

 found most abundantly in the seeds, as of flax, rape and 

 cotton, which are often called oil seeds. Fat occurs in 

 the form of minute oil globules within the plant cell, and 

 is removed mechanically by the aid of heat and pressure, 



