The Manufacture of Food 41 



The production of fats. In addition to carbohydrates, plants 

 make and use two other important classes of foods : fats and pro- 

 tein. The fats are quite similar to the carbohydrates in composi- 

 tion. They contain the same chemical elements : carbon, hydro- 

 gen, and oxygen. The proportion of the oxygen to carbon, 

 however, is smaller. At ordinary temperatures fats occur in 

 plants both as solids and liquids. The liquid fats are commonly 

 called oils. They are probably made directly from the carbo- 

 hydrates, for the plant has no special fat-producing apparatus 

 comparable with the carbohydrate-producing chloroplasts of the 

 leaves. The chemical changes are probably effected by the 

 protoplasm ; therefore fat can be formed in any living part of 

 the plant. 



In some plants belonging to the hly family (the onion, for 

 example) small drops of oil appear in the cells of the leaf as the 

 first visible product of food manufacture. The primary product 

 of photosynthesis (probably glucose) is changed directly into oil 

 when it accumulates, instead of into starch as it is in the leaves of 

 most plants. Starch does not form in these leaves at any time, 

 but when the materials of which the fats are composed are trans- 

 ferred and accumulate in the underground bulbs of these plants, 

 they then assume the form of starch. This emphasizes the close 

 relationship existing between starch, glucose, and fat. 



Fats and oils, like starch, are inactive storage substances ; that 

 is, before being used or transferred they must be converted into 

 substances soluble in water. Although fats are widely dis- 

 tributed in the plant body, they are especially abundant in seeds 

 and fruits. Some of the commonest fats and oils of commerce 

 derived from plants are corn, coconut, cottonseed, linseed, castor, 

 pea, peanut, and olive oils, and cocoa butter. 



Fats are formed from carbohydrates by two different series of 

 chemical changes. In the first of these series the carbohydrates 

 are changed to fatty acids, the more important of which are oleic, 

 palmitic, and stearic. In the second series of chemical changes 



