ROOTS. 30 
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, Fig. 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. yg. ne mE Dahlia, Rp tes: 
47. Lxtent of the Root-System. oN tee eee are Stored 
— 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 
s, cut-off stems of the plant. 
