CARBOHYDRATES, ACIDS, FATS, OILS 79 



proportion of other compounds, and besides, more or less 

 cellulose is dissolved by the acid and alkali treatment, 

 so that the percentages of crude fiber given in food tables 

 only approximately measure the cellulose present. 



All plant tissue is made up of cells, the walls of which 

 are chiefly or wholly cellulose. It is this substance out of 

 which is built the framework of the plant, and which 

 gives toughness and rigidity to certain of its parts. The 

 more of this plant tissue contains, the more tenacious it 

 is, other things being equal, and the more difficult of 

 mastication. 



The proportions of cellulose in the different parts of a 

 plant are greatly unlike. It is usually most abundant in 

 the stem, with less in the foliage and least in the fruit. 

 With vegetables like potatoes and turnips, the leaves are 

 much richer in fiber than the tubers or roots, which con- 

 tain a comparatively small proportion. Of the grains or 

 seeds, considerable is present in the outer coatings, while 

 but little is found in the interior. Vegetables such as 

 celery, lettuce, beets, and turnips are relatively rich in 

 crude fiber, while tubers, flours, and meals contain only 

 small amounts. In certain by-products from the grains, 

 like bran, which is made up mostly of the seed coatings, 

 fiber is present in fairly large proportions, while in flour 

 derived from the inner parts of the grain, the percentage 

 is almost negligible. 



The stage of growth at which a plant is used for food 

 purposes has a marked influence upon the proportion of 

 crude fiber. In young, actively growing vegetable tissue, 

 the cell-walls are thin, but, as the plant increases in age, 

 these thicken chiefly through the deposition of cellulose. 

 In general, the toughness and hardness of mature plants, 

 as compared with young are due to the increased pro- 



