ROOTS 39 



The first season's work consists mainly in producing the 

 food wliicli is stored in the roots. To sach storage is 

 due their characteristic fleshy appearance. If this root is 

 planted in the following spring, it feeds the rapidly grow- 

 ing stem which proceeds from the bud at its summit, and 

 an abundant crop of flowers and seed soon follows ; while 

 the root, if examined in late summer, will be found to be 

 withered, with its store of reserve material quite exhausted. 



The roots of the dahlia (Fig. 17), the sweet potato, and a 

 multitude of othev perennials, or plants which live for many 

 years, contain much stored plant-food. Many such plants die 

 to the ground at the beginning of \^'inter, and in spring make 

 a rapid growth from the materials laid up in the roots. 



50. Extent of the Root-System. — The total length of 

 the roots of ordinary plants is much greater than is usually 

 supposed. They are so closely packed in the earth that 

 only a few of the roots are seen at a time during the 

 process of transplanting, and when a plant is pulled or dug 

 up in the ordinary way a large part of the whole mass of 

 roots is broken off and left behind. A few plants have 

 been carefully studied to ascertain the total weight and 

 length of the roots. Those of winter wheat have been 

 found to extend to a depth of seven feet. By weighing 

 the whole root-system of a plant and then weighing a 

 known length of a root of average diameter, the total 

 length of the roots may be estimated. In this way the 

 roots of an oat plant have been calculated to measure 

 about 154 feet ; that is, all the roots, if cut off and strung 

 together end to end, would reach that distance. 



51. Absorption of Water by Roots. — ]Many experiments 

 on the cultivation of corn, wheat, oats, beans, peas, and 

 other familiar plants in water have proved that some plants, 



