38 THE OAK 
grows out at an obtuse angle from the primary root, 
and not vertically downwards, and as it does so a 
similar wave of root-hairs is developed along it; thus a 
series of nearly horizontal radiating cylinders of soil 
are placed under contribution as before. Then the 
secondary rootlets emit tertiary rootlets in all direc- 
tions—these and the rootlets of a higher order growing 
without any particular reference to the direction of 
gravitation, light, &«.—and so place successive cylin- 
ders of soil in all directions under contribution as 
before. By this time, however, the symmetry of the 
root-system is being disturbed because some of the 
rootlets meet with stones or other obstacles, others get 
dried up or frozen, or gnawed off or otherwise injured, 
and the varying directions in which new growths start 
and in which the resistances are least, influence the very 
various shapes of the tangled mass of roots now per- 
meating the soil in all directions. 
These roots supply the ever-increasing needs for water 
of the shoot-system, the leaf-surface of which is becoming 
larger and larger, and as the greater volume of water 
from the gathering rootlets has all to enter the stem vid: 
the upper part of the main root, we are not surprised to 
find that the latter thickens, as does the stem; and so 
with all the older roots—they no longer act as absorb- 
ing roots, but become merely larger and larger channels 
for water, and girder-like supporting organs. 
