136 ROOTS 
the shoot, for the larger the shoot, the larger the root system nec- 
essary to supply the adequate amount of water and mineral mat- 
ter, and to furnish sufficient anchorage. As to the size of the 
roots of a plant, that depends upon the size of the shoot, the num- 
ber of roots, and the distances of roots from the stem. The re- 
lation of the size of roots to that of the shoot is well shown in case 
of trees, where the roots directly connected with the stem and 
known as main roots increase in diameter from a few millimeters 
often to a foot or more as the shoot passes from the seedling to the 
mature stage. Where there is only one main root, as in Alfalfa 
and the Dandelion, its size is directly in proportion to the size of 
the shoot, usually being as large or even larger in diameter than 
the short stem of the crown. On the other hand, when the roots 
leading from the stem are numerous, as in the Grasses and 
numerous other plants, all are relatively small. As to the size 
of a branch root, that depends much upon its distance from the 
stem or main root, for all roots branch and rebranch until the 
branches are fibrous-like, usually being a millimeter or less in 
diameter at their tips. It is in connection with these fiber-like 
branches, which are the absorptive regions, that roots show most 
uniformity; for the roots of all plants taper down to these fiber- 
like branches, which are practically uniform in size for all plants. 
This uniformity in size is probably due to the fact that only 
roots with a very small diameter are efficient absorbers. 
The texture of roots is always soft at the tips where the cells 
active in division, elongation, and absorption have thin cellulose 
walls, which readily yield to pressure or strains. But not far back 
of the absorptive region there are formed strengthening fibers, 
which afford a toughness that enables the root to endure the 
strains in connection with its anchorage function. Furthermore, 
roots, in their older regions, are covered with cork which adds 
firmness to the texture. In shrubs and trees the roots, in their 
older regions, become as woody and just as hard as the stems. 
' As to duration, roots may be short-lived, serving the plant only 
in the seedling stage, as in case of temporary roots, or they may 
last as long as the plant, as in case of permanent roots. The life 
of permanent roots is one, two, or many years according to 
whether or not the plant is annual, biennial, or perennial. 
Interdependence of Shoot and Root. — Upon the roots the 
shoot depends for watcr, mineral matter, and anchorage, while 
