BOOTS. 



33 



Fig. 20. — Roots of Dahlia, thick- 

 ened and containing Stored 

 No urishment. 

 s, cut-off stems of the plant. 



planted in the following spring, it feeds the rapidly growing 

 stem which proceeds from the bud at its summit, and an abun- 

 dant 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, Tig. 20, 

 and of many other perennials, or 

 plants which live for many years, 

 contain much stored plant-food. 

 Such plants die to the ground at 

 the beginning of winter, and in 

 spring make a rapid growth from 

 the materials laid up in the roots. 



47. Extent of the Hoot-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 150 feet ; that is, all the 

 roots, if cut off and strung together end to end, would reach 

 that distance. 



Single roots of large trees often extend horizontally to 

 great distances, but it is not often possible readily to trace 

 the entire depth to which they extend. Roots of oak trees 



