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BIOLOGY AND HUMAN LIFE 



P 



Fig. 67. Diagram of root structure 



The skin, or outer layer, c, is called the 

 epidermis. Under this comes the bark, c, 

 or cortex. The central portion, running 

 lengthwise of the root, cyl, is the central 

 cylinder and corresponds to the wood of 

 a stem. In either a cross section or a 

 longitudinal section you can distinguish 

 the central cylinder from the cortex. 

 Some of the long cells in the central cyl- 

 inder serve as tubes or vessels through 

 which liquids move up into the stem. 

 Other vessels in the central cylinder 

 carry food materials from the leaves and 

 stems down into the growing parts of the 

 root. In addition to the cells which form 

 ducts there are others with thickened 

 walls. These fibers add to the toughness 

 and rigidity of the cylinder. Bundles of 

 fibers with water-conducting vessels or 

 of fibers with food-conducting vessels are 

 called fibrovascular bundles, fibro mean- 

 ing ''of fibers" and vascular meaning 

 "of vessels" or tubes, p, the pith 



carrying, or bast, system. 

 Growth in length results from 

 the formation of new cells by 

 a special growing layer near 

 the tip of the root. 



95. Uses of roots. Many 

 plants have the habit of de- 

 positing food in their rocts : 

 starch, sugar, and proteins. 

 Although our fleshy vege- 

 tables contain from about 

 80 per cent to 90 per cent of 

 water after the skin is re- 

 moved, they are still worth 

 using for their organic sub- 

 stances and the useful min- 

 eral salts. These vegetables 

 have a relatively large bulk 

 of cellulose, which is helpful 

 in stirring the intestines to 

 action (seepage 154). 



Fleshy roots are used in 

 large quantities as fodder for 

 cattle. Some roots serve also 

 as sources of drugs and flavor- 

 ings, as licorice root, sassafras 

 root, and sarsaparilla. 



Because root hairs adhere 

 very closely to grains of sand 

 in the soil, roots are very 

 effective in binding the soil, 

 enabling it to withstand the 

 wearing away by water and 

 by wind. For this reason cer- 

 tain kinds of grasses are some- 

 times planted on sandy strips 



